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					                    .NET Framework Frequently Asked Questions
                        This FAQ tries to answer some commonly asked questions about the
fundamentals of the .NET Framework - topics like assemblies, garbage collection, security, interop
with COM, and remoting. The most commonly-used parts of the class library are also covered.
Other aspects of the .NET Framework such as ASP.NET, ADO.NET and WinForms are not covered.

This FAQ was inspired by discussions on the DOTNET mailing list. The list has now been split into several
DOTNET-X lists - for details see http://discuss.develop.com/.

Christophe Lauer has translated the FAQ into French - you can find it at http://www.dotnet-
fr.org/documents/andy_faqdotnet_fr.html

Royal has translated the FAQ into Chinese - you can find it at
http://www.royaloo.com/articles/articles_2002/dotNetFAQ.htm

Disclaimer: The content of this FAQ is just my interpretation of information gleaned from various sources,
including postings to the DOTNET-X mailing lists and various MS documents. The answers are not necessarily
correct or up-to-date. Note that this FAQ has no official connection to the DOTNET-X mailing lists, or to
Developmentor (the company who host the lists), or to Microsoft.

Revision history:


21-Nov-02               Added link to Christophe Lauer's French translation.
9-Jul-02                Added Serialization section
                        Overhaul of Resources section, including new Recommended
7-Jun-02
                        Books and Weblogs topics.
17-Jan-02               Minor update to reflect arrival of version 1.
20-Aug-01               Updated all the code samples to be fully compatible with Beta 2.
28-Jun-01               Minor update to reflect arrival of Beta 2.
18-Nov-00               Added Tracing sub-section to the Class Library section.
13-Nov-00               Updated for arrival of Beta 1.
09-Nov-00               Started Class Library section.
03-Nov-00               Added section on IL.
14-Oct-00               Added section on Code Access Security.
29-Aug-00               Started revision history.
29-Jul-00 to 28-Aug-
                     Miscellaneous (unrecorded) updates.
00
29-Jul-00               Posted first version.




Contents


          1. Introduction

               o   1.1 What is .NET?

               o   1.2 Does .NET only apply to people building web-sites?

               o   1.3 When was .NET announced?

               o   1.4 When was the first version of .NET released?

               o   1.5 What tools can I use to develop .NET applications?
        o   1.6 What platforms does the .NET Framework run on?

        o   1.7 What languages does the .NET Framework support?

        o   1.8 Will the .NET Framework go through a standardisation process?



   2. Basic terminology

        o   2.1 What is the CLR?

        o   2.2 What is the CTS?

        o   2.3 What is the CLS?

        o   2.4 What is IL?

        o   2.5 What is C#?

        o   2.6 What does 'managed' mean in the .NET context?

        o   2.7 What is reflection?



   3. Assemblies

        o   3.1 What is an assembly?

        o   3.2 How can I produce an assembly?

        o   3.3 What is the difference between a private assembly and a shared assembly?

        o   3.4 How do assemblies find each other?

        o   3.5 How does assembly versioning work?



   4. Application Domains

        o   4.1 What is an Application Domain?

        o   4.2 How does an AppDomain get created?

        o   4.3 Can I write my own .NET host?



   5. Garbage Collection

        o   5.1 What is garbage collection?

        o   5.2 Is it true that objects don't always get destroyed immediately when the last reference

            goes away?

        o   5.3 Why doesn't the .NET runtime offer deterministic destruction?

        o   5.4 Is the lack of deterministic destruction in .NET a problem?

        o   5.5 Does non-deterministic destruction affect the usage of COM objects from managed code?

        o   5.6 I've heard that Finalize methods should be avoided. Should I implement Finalize on my
            class?
        o    5.7 Do I have any control over the garbage collection algorithm?

        o    5.8 How can I find out what the garbage collector is doing?



   6. Serialization

        o    6.1 What is serialization?

        o    6.2 Does the .NET Framework have in-built support for serialization?

        o    6.3 I want to serialize instances of my class. Should I use XmlSerializer, SoapFormatter or
             BinaryFormatter?

        o    6.4 Can I customise the serialization process?

        o    6.5 Why is XmlSerializer so slow?

        o    6.6 Why do I get errors when I try to serialize a Hashtable?

        o    6.7 XmlSerializer is throwing a generic "There was an error reflecting MyClass" error. How do

             I find out what the problem is?



   7. Attributes

        o    7.1 What are attributes?

        o    7.2 Can I create my own metadata attributes?

        o    7.3 Can I create my own context attributes?



   8. Code Access Security

        o    8.1 What is Code Access Security (CAS)?

        o    8.2 How does CAS work?

        o    8.3 Who defines the CAS code groups?

        o    8.4 How do I define my own code group?

        o    8.5 How do I change the permission set for a code group?

        o    8.6 Can I create my own permission set?

        o    8.7 I'm having some trouble with CAS. How can I diagnose my problem?

        o    8.8 I can't be bothered with all this CAS stuff. Can I turn it off?



   9. Intermediate Language (IL)

        o    9.1 Can I look at the IL for an assembly?

        o    9.2 Can source code be reverse-engineered from IL?

        o    9.3 How can I stop my code being reverse-engineered from IL?

        o    9.4 Can I write IL programs directly?
        o    9.5 Can I do things in IL that I can't do in C#?



   10. Implications for COM

        o    10.1 Is COM dead?

        o    10.2 Is DCOM dead?

        o    10.3 Is MTS/COM+ dead?

        o    10.4 Can I use COM components from .NET programs?

        o    10.5 Can I use .NET components from COM programs?

        o    10.6 Is ATL redundant in the .NET world?



   11. Miscellaneous

        o    11.1 How does .NET remoting work?

        o    11.2 How can I get at the Win32 API from a .NET program?



   12. Class Library

        o    12.1 File I/O

                       12.1.1 How do I read from a text file?

                       12.1.2 How do I write to a text file?

                       12.1.3 How do I read/write binary files?

        o    12.2 Text Processing

                       12.2.1 Are regular expressions supported?

        o    12.3 Internet

                       12.3.1 How do I download a web page?

                       12.3.2 How do I use a proxy?

        o    12.4 XML

                       12.4.1 Is DOM supported?

                       12.4.2 Is SAX supported?

                       12.4.3 Is XPath supported?

        o    12.5 Threading

                       12.5.1 Is multi-threading supported?

                       12.5.2 How do I spawn a thread?

                       12.5.3 How do I stop a thread?

                       12.5.4 How do I use the thread pool?

                       12.5.5 How do I know when my thread pool work item has completed?
                          12.5.6 How do I prevent concurrent access to my data?

             o    12.6 Tracing

                          12.6.1 Is there built-in support for tracing/logging?

                          12.6.2 Can I redirect tracing to a file?

                          12.6.3 Can I customise the trace output?



        13. Resources

             o    13 Recommended books




                                               .NET

1. Introduction

        1. 1.1 What is .NET?

That's difficult to sum up in a sentence. According to Microsoft, .NET is a "revolutionary new platform, built on
open Internet protocols and standards, with tools and services that meld computing and communications in
new ways".

A more practical definition would be that .NET is a new environment for developing and running software
applications, featuring ease of development of web-based services, rich standard run-time services available to
components written in a variety of programming languages, and inter-language and inter-machine
interoperability.

Note that when the term ".NET" is used in this FAQ it refers only to the new .NET runtime and associated
technologies. This is sometimes called the ".NET Framework". This FAQ does NOT cover any of the various
other existing and new products/technologies that Microsoft are attaching the .NET name to (e.g. SQL
Server.NET).

        2. 1.2 Does .NET only apply to people building web-sites?

No. If you write any Windows software (using ATL/COM, MFC, VB, or even raw Win32), .NET may offer a viable
alternative (or addition) to the way you do things currently. Of course, if you do develop web sites, then .NET
has lots to interest you - not least ASP.NET.

        3. 1.3 When was .NET announced?

Bill Gates delivered a keynote at Forum 2000, held June 22, 2000, outlining the .NET 'vision'. The July 2000
PDC had a number of sessions on .NET technology, and delegates were given CDs containing a pre-release
version of the .NET framework/SDK and Visual Studio.NET.

        4. 1.4 When was the first version of .NET released?

The final version of the 1.0 SDK and runtime was made publicly available around 6pm PST on 15-Jan-2002. At
the same time, the final version of Visual Studio.NET was made available to MSDN subscribers.

        5. 1.5 What tools can I use to develop .NET applications?

There are a number of tools, described here in ascending order of cost:
        .NET Framework SDK: The SDK is free and includes command-line compilers for C++, C#, and
         VB.NET and various other utilities to aid development.
        ASP.NET Web Matrix: This is a free ASP.NET development environment from Microsoft. As well as a
         GUI development environment, the download includes a simple web server that can be used instead
         of IIS to host ASP.NET apps. This opens up ASP.NET development to users of Windows XP Home
         Edition, which cannot run IIS.
        Microsoft Visual C# .NET Standard 2003: This is a cheap (around $100) version of Visual Studio
         limited to one language and also with limited wizard support. For example, there's no wizard support
         for class libraries or custom UI controls. Useful for beginners to learn with, or for savvy developers
         who can work around the deficiencies in the supplied wizards. As well as C#, there are VB.NET and
         C++ versions.
        Microsoft Visual Studio.NET Professional 2003: If you have a license for Visual Studio 6.0, you can get
         the upgrade. You can also upgrade from VS.NET 2002 for a token $30. Visual Studio.NET includes
         support for all the MS languages (C#, C++, VB.NET) and has extensive wizard support.

At the top end of the price spectrum are the Visual Studio.NET 2003 Enterprise and Enterprise Architect
editions. These offer extra features such as Visual Sourcesafe (version control), and performance and analysis
tools. Check out the Visual Studio.NET Feature Comparison at
http://msdn.microsoft.com/vstudio/howtobuy/choosing.asp.

        6. 1.6 What platforms does the .NET Framework run on?

The runtime supports Windows XP, Windows 2000, NT4 SP6a and Windows ME/98. Windows 95 is not
supported. Some parts of the framework do not work on all platforms - for example, ASP.NET is only
supported on Windows XP and Windows 2000. Windows 98/ME cannot be used for development.

IIS is not supported on Windows XP Home Edition, and so cannot be used to host ASP.NET. However, the
ASP.NET Web Matrix web server does run on XP Home.

The Mono project is attempting to implement the .NET framework on Linux.

        7. 1.7 What languages does the .NET Framework support?

MS provides compilers for C#, C++, VB and JScript. Other vendors have announced that they intend to
develop .NET compilers for languages such as COBOL, Eiffel, Perl, Smalltalk and Python.

        8. 1.8 Will the .NET Framework go through a standardisation process?

From http://msdn.microsoft.com/net/ecma/: "On December 13, 2001, the ECMA General Assembly ratified the
C# and common language infrastructure (CLI) specifications into international standards. The ECMA standards
will be known as ECMA-334 (C#) and ECMA-335 (the CLI)."

2. Basic terminology

        9. 2.1 What is the CLR?

CLR = Common Language Runtime. The CLR is a set of standard resources that (in theory) any .NET program
can take advantage of, regardless of programming language. Robert Schmidt (Microsoft) lists the following
CLR resources in his MSDN PDC# article:


        Object-oriented programming model (inheritance, polymorphism, exception handling, garbage
         collection)
        Security model
        Type system
        All .NET base classes
        Many .NET framework classes
        Development, debugging, and profiling tools
        Execution and code management
        IL-to-native translators and optimizers

What this means is that in the .NET world, different programming languages will be more equal in capability
than they have ever been before, although clearly not all languages will support all CLR services.

        10.       2.2 What is the CTS?

CTS = Common Type System. This is the range of types that the .NET runtime understands, and therefore that
.NET applications can use. However note that not all .NET languages will support all the types in the CTS. The
CTS is a superset of the CLS.

        11.       2.3 What is the CLS?

CLS = Common Language Specification. This is a subset of the CTS which all .NET languages are expected to
support. The idea is that any program which uses CLS-compliant types can interoperate with any .NET
program written in any language.

In theory this allows very tight interop between different .NET languages - for example allowing a C# class to
inherit from a VB class.

        12.       2.4 What is IL?

IL = Intermediate Language. Also known as MSIL (Microsoft Intermediate Language) or CIL (Common
Intermediate Language). All .NET source code (of any language) is compiled to IL. The IL is then converted to
machine code at the point where the software is installed, or at run-time by a Just-In-Time (JIT) compiler.

        13.       2.5 What is C#?

C# is a new language designed by Microsoft to work with the .NET framework. In their "Introduction to C#"
whitepaper, Microsoft describe C# as follows:

"C# is a simple, modern, object oriented, and type-safe programming language derived from C and C++. C#
(pronounced ―C sharp‖) is firmly planted in the C and C++ family tree of languages, and will immediately be
familiar to C and C++ programmers. C# aims to combine the high productivity of Visual Basic and the raw
power of C++."

Substitute 'Java' for 'C#' in the quote above, and you'll see that the statement still works pretty well :-).

If you are a C++ programmer, you might like to check out my C# FAQ.

        14.       2.6 What does 'managed' mean in the .NET context?

The term 'managed' is the cause of much confusion. It is used in various places within .NET, meaning slightly
different things.

Managed code: The .NET framework provides several core run-time services to the programs that run within
it - for example exception handling and security. For these services to work, the code must provide a minimum
level of information to the runtime. Such code is called managed code. All C# and Visual Basic.NET code is
managed by default. VS7 C++ code is not managed by default, but the compiler can produce managed code
by specifying a command-line switch (/com+).

Managed data: This is data that is allocated and de-allocated by the .NET runtime's garbage collector. C#
and VB.NET data is always managed. VS7 C++ data is unmanaged by default, even when using the /com+
switch, but it can be marked as managed using the __gc keyword.
Managed classes: This is usually referred to in the context of Managed Extensions (ME) for C++. When using
ME C++, a class can be marked with the __gc keyword. As the name suggests, this means that the memory
for instances of the class is managed by the garbage collector, but it also means more than that. The class
becomes a fully paid-up member of the .NET community with the benefits and restrictions that brings. An
example of a benefit is proper interop with classes written in other languages - for example, a managed C++
class can inherit from a VB class. An example of a restriction is that a managed class can only inherit from one
base class.

       15.        2.7 What is reflection?

All .NET compilers produce metadata about the types defined in the modules they produce. This metadata is
packaged along with the module (modules in turn are packaged together in assemblies), and can be accessed
by a mechanism called reflection. The System.Reflection namespace contains classes that can be used to
interrogate the types for a module/assembly.

Using reflection to access .NET metadata is very similar to using ITypeLib/ITypeInfo to access type library data
in COM, and it is used for similar purposes - e.g. determining data type sizes for marshaling data across
context/process/machine boundaries.

Reflection can also be used to dynamically invoke methods (see System.Type.InvokeMember), or even create
types dynamically at run-time (see System.Reflection.Emit.TypeBuilder).

3. Assemblies

       16.        3.1 What is an assembly?

An assembly is sometimes described as a logical .EXE or .DLL, and can be an application (with a main entry
point) or a library. An assembly consists of one or more files (dlls, exes, html files etc), and represents a group
of resources, type definitions, and implementations of those types. An assembly may also contain references
to other assemblies. These resources, types and references are described in a block of data called a manifest.
The manifest is part of the assembly, thus making the assembly self-describing.

An important aspect of assemblies is that they are part of the identity of a type. The identity of a type is the
assembly that houses it combined with the type name. This means, for example, that if assembly A exports a
type called T, and assembly B exports a type called T, the .NET runtime sees these as two completely different
types. Furthermore, don't get confused between assemblies and namespaces - namespaces are merely a
hierarchical way of organising type names. To the runtime, type names are type names, regardless of whether
namespaces are used to organise the names. It's the assembly plus the typename (regardless of whether the
type name belongs to a namespace) that uniquely indentifies a type to the runtime.

Assemblies are also important in .NET with respect to security - many of the security restrictions are enforced
at the assembly boundary.

Finally, assemblies are the unit of versioning in .NET - more on this below.

       17.        3.2 How can I produce an assembly?

The simplest way to produce an assembly is directly from a .NET compiler. For example, the following C#
program:

    public class CTest
    {
           public CTest()
           {
                       System.Console.WriteLine( "Hello from CTest" );
           }
    }

can be compiled into a library assembly (dll) like this:
    csc /t:library ctest.cs

You can then view the contents of the assembly by running the "IL Disassembler" tool that comes with the
.NET SDK.

Alternatively you can compile your source into modules, and then combine the modules into an assembly
using the assembly linker (al.exe). For the C# compiler, the /target:module switch is used to generate a
module instead of an assembly.

        18. 3.3 What is the difference between a private assembly and a shared assembly?


        Location and visibility: A private assembly is normally used by a single application, and is stored in
         the application's directory, or a sub-directory beneath. A shared assembly is normally stored in the
         global assembly cache, which is a repository of assemblies maintained by the .NET runtime. Shared
         assemblies are usually libraries of code which many applications will find useful, e.g. the .NET
         framework classes.


        Versioning: The runtime enforces versioning constraints only on shared assemblies, not on private
         assemblies.

        19. 3.4 How do assemblies find each other?

By searching directory paths. There are several factors which can affect the path (such as the AppDomain
host, and application configuration files), but for private assemblies the search path is normally the
application's directory and its sub-directories. For shared assemblies, the search path is normally same as the
private assembly path plus the shared assembly cache.

        20. 3.5 How does assembly versioning work?

Each assembly has a version number called the compatibility version. Also each reference to an assembly
(from another assembly) includes both the name and version of the referenced assembly.

The version number has four numeric parts (e.g. 5.5.2.33). Assemblies with either of the first two parts
different are normally viewed as incompatible. If the first two parts are the same, but the third is different, the
assemblies are deemed as 'maybe compatible'. If only the fourth part is different, the assemblies are deemed
compatible. However, this is just the default guideline - it is the version policy that decides to what extent
these rules are enforced. The version policy can be specified via the application configuration file.

Remember: versioning is only applied to shared assemblies, not private assemblies.

4. Application Domains

        21. 4.1 What is an Application Domain?

An AppDomain can be thought of as a lightweight process. Multiple AppDomains can exist inside a Win32
process. The primary purpose of the AppDomain is to isolate an application from other applications.

Win32 processes provide isolation by having distinct memory address spaces. This is effective, but it is
expensive and doesn't scale well. The .NET runtime enforces AppDomain isolation by keeping control over the
use of memory - all memory in the AppDomain is managed by the .NET runtime, so the runtime can ensure
that AppDomains do not access each other's memory.

        22. 4.2 How does an AppDomain get created?

AppDomains are usually created by hosts. Examples of hosts are the Windows Shell, ASP.NET and IE. When
you run a .NET application from the command-line, the host is the Shell. The Shell creates a new AppDomain
for every application.
AppDomains can also be explicitly created by .NET applications. Here is a C# sample which creates an
AppDomain, creates an instance of an object inside it, and then executes one of the object's methods. Note
that you must name the executable 'appdomaintest.exe' for this code to work as-is.

    using System;
    using System.Runtime.Remoting;

    public class CAppDomainInfo : MarshalByRefObject
    {
           public string GetAppDomainInfo()
           {
                       return "AppDomain = " + AppDomain.CurrentDomain.FriendlyName;
           }

    }

    public class App
    {
      public static int Main()
      {
                       AppDomain ad = AppDomain.CreateDomain( "Andy's new domain", null, null );
                       ObjectHandle oh = ad.CreateInstance( "appdomaintest", "CAppDomainInfo" );
                       CAppDomainInfo adInfo = (CAppDomainInfo)(oh.Unwrap());
                       string info = adInfo.GetAppDomainInfo();

                       Console.WriteLine( "AppDomain info: " + info );
                       return 0;
        }
    }

        23. 4.3 Can I write my own .NET host?

Yes. For an example of how to do this, take a look at the source for the dm.net moniker developed by Jason
Whittington and Don Box (http://staff.develop.com/jasonw/clr/readme.htm ). There is also a code sample in
the .NET SDK called CorHost.

5. Garbage Collection

        24. 5.1 What is garbage collection?

Garbage collection is a system whereby a run-time component takes responsibility for managing the lifetime of
objects and the heap memory that they occupy. This concept is not new to .NET - Java and many other
languages/runtimes have used garbage collection for some time.

        25. 5.2 Is it true that objects don't always get destroyed immediately when the last
           reference goes away?

Yes. The garbage collector offers no guarantees about the time when an object will be destroyed and its
memory reclaimed.

There is an interesting thread in the archives, started by Chris Sells, about the implications of non-
deterministic destruction of objects in C#:
http://discuss.develop.com/archives/wa.exe?A2=ind0007&L=DOTNET&P=R24819

In October 2000, Microsoft's Brian Harry posted a lengthy analysis of the problem:
http://discuss.develop.com/archives/wa.exe?A2=ind0010A&L=DOTNET&P=R28572

Chris Sells' response to Brian's posting is here:
http://discuss.develop.com/archives/wa.exe?A2=ind0010C&L=DOTNET&P=R983
        26. 5.3 Why doesn't the .NET runtime offer deterministic destruction?

Because of the garbage collection algorithm. The .NET garbage collector works by periodically running through
a list of all the objects that are currently being referenced by an application. All the objects that it doesn't find
during this search are ready to be destroyed and the memory reclaimed. The implication of this algorithm is
that the runtime doesn't get notified immediately when the final reference on an object goes away - it only
finds out during the next sweep of the heap.

Futhermore, this type of algorithm works best by performing the garbage collection sweep as rarely as
possible. Normally heap exhaustion is the trigger for a collection sweep.

        27. 5.4 Is the lack of deterministic destruction in .NET a problem?

It's certainly an issue that affects component design. If you have objects that maintain expensive or scarce
resources (e.g. database locks), you need to provide some way for the client to tell the object to release the
resource when it is done. Microsoft recommend that you provide a method called Dispose() for this purpose.
However, this causes problems for distributed objects - in a distributed system who calls the Dispose()
method? Some form of reference-counting or ownership-management mechanism is needed to handle
distributed objects - unfortunately the runtime offers no help with this.

        28. 5.5 Does non-deterministic destruction affect the usage of COM objects from managed
           code?

Yes. When using a COM object from managed code, you are effectively relying on the garbage collector to call
the final release on your object. If your COM object holds onto an expensive resource which is only cleaned-up
after the final release, you may need to provide a new interface on your object which supports an explicit
Dispose() method.

        29. 5.6 I've heard that Finalize methods should be avoided. Should I implement Finalize on
           my class?

An object with a Finalize method is more work for the garbage collector than an object without one. Also there
are no guarantees about the order in which objects are Finalized, so there are issues surrounding access to
other objects from the Finalize method. Finally, there is no guarantee that a Finalize method will get called on
an object, so it should never be relied upon to do clean-up of an object's resources.

Microsoft recommend the following pattern:

    public class CTest : IDisposable
    {
           public void Dispose()
           {
                       ... // Cleanup activities
                       GC.SuppressFinalize(this);
           }

            ~CTest()    // C# syntax hiding the Finalize() method
            {
                        Dispose();
            }
    }

In the normal case the client calls Dispose(), the object's resources are freed, and the garbage collector is
relieved of its Finalizing duties by the call to SuppressFinalize(). In the worst case, i.e. the client forgets to call
Dispose(), there is a reasonable chance that the object's resources will eventually get freed by the garbage
collector calling Finalize(). Given the limitations of the garbage collection algorithm this seems like a pretty
reasonable approach.
       30. 5.7 Do I have any control over the garbage collection algorithm?

A little. For example, the System.GC class exposes a Collect method - this forces the garbage collector to
collect all unreferenced objects immediately.

       31. 5.8 How can I find out what the garbage collector is doing?

Lots of interesting statistics are exported from the .NET runtime via the '.NET CLR xxx' performance counters.
Use Performance Monitor to view them.

6. Serialization

       32. 6.1 What is serialization?

Serialization is the process of converting an object into a stream of bytes. Deserialization is the opposite
process of creating an object from a stream of bytes. Serialization/Deserialization is mostly used to transport
objects (e.g. during remoting), or to persist objects (e.g. to a file or database).

       33. 6.2 Does the .NET Framework have in-built support for serialization?

There are two separate mechanisms provided by the .NET class library - XmlSerializer and
SoapFormatter/BinaryFormatter. Microsoft uses XmlSerializer for Web Services, and uses
SoapFormatter/BinaryFormatter for remoting. Both are available for use in your own code.

       34. 6.3 I want to serialize instances of my class. Should I use XmlSerializer, SoapFormatter
          or BinaryFormatter?

It depends. XmlSerializer has severe limitations such as the requirement that the target class has a
parameterless constructor, and only public read/write properties and fields can be serialized. However, on the
plus side, XmlSerializer has good support for customising the XML document that is produced or consumed.
XmlSerializer's features mean that it is most suitable for cross-platform work, or for constructing objects from
existing XML documents.

SoapFormatter and BinaryFormatter have fewer limitations than XmlSerializer. They can serialize private fields,
for example. However they both require that the target class be marked with the [Serializable] attribute, so
like XmlSerializer the class needs to be written with serialization in mind. Also there are some quirks to watch
out for - for example on deserialization the constructor of the new object is not invoked.

The choice between SoapFormatter and BinaryFormatter depends on the application. BinaryFormatter makes
sense where both serialization and deserialization will be performed on the .NET platform and where
performance is important. SoapFormatter generally makes more sense in all other cases, for ease of
debugging if nothing else.

       35. 6.4 Can I customise the serialization process?

Yes. XmlSerializer supports a range of attributes that can be used to configure serialization for a particular
class. For example, a field or property can be marked with the [XmlIgnore] attribute to exclude it from
serialization. Another example is the [XmlElement] attribute, which can be used to specify the XML element
name to be used for a particular property or field.

Serialization via SoapFormatter/BinaryFormatter can also be controlled to some extent by attributes. For
example, the [NonSerialized] attribute is the equivalent of XmlSerializer's [XmlIgnore] attribute. Ultimate
control of the serialization process can be acheived by implementing the the ISerializable interface on the class
whose instances are to be serialized.

       36. 6.5 Why is XmlSerializer so slow?

There is a once-per-process-per-type overhead with XmlSerializer. So the first time you serialize or deserialize
an object of a given type in an application, there is a significant delay. This normally doesn't matter, but it may
mean, for example, that XmlSerializer is a poor choice for loading configuration settings during startup of a
GUI application.

        37. 6.6 Why do I get errors when I try to serialize a Hashtable?

XmlSerializer will refuse to serialize instances of any class that implements IDictionary, e.g. Hashtable.
SoapFormatter and BinaryFormatter do not have this restriction.

        38. 6.7 XmlSerializer is throwing a generic "There was an error reflecting MyClass" error.
           How do I find out what the problem is?

Look at the InnerException property of the exception that is thrown to get a more specific error message.

7. Attributes

        39. 7.1 What are attributes?

There are at least two types of .NET attribute. The first type I will refer to as a metadata attribute - it allows
some data to be attached to a class or method. This data becomes part of the metadata for the class, and (like
other class metadata) can be accessed via reflection. An example of a metadata attribute is [serializable],
which can be attached to a class and means that instances of the class can be serialized.

    [serializable] public class CTest {}

The other type of attribute is a context attribute. Context attributes use a similar syntax to metadata attributes
but they are fundamentally different. Context attributes provide an interception mechanism whereby instance
activation and method calls can be pre- and/or post-processed. If you've come across Keith Brown's universal
delegator you'll be familiar with this idea.

        40. 7.2 Can I create my own metadata attributes?

Yes. Simply derive a class from System.Attribute and mark it with the AttributeUsage attribute. For example:

    [AttributeUsage(AttributeTargets.Class)]
    public class InspiredByAttribute : System.Attribute
    {
           public string InspiredBy;

           public InspiredByAttribute( string inspiredBy )
           {
                       InspiredBy = inspiredBy;
           }
    }


    [InspiredBy("Andy Mc's brilliant .NET FAQ")]
    class CTest
    {
    }


    class CApp
    {
           public static void Main()
           {
                       object[] atts = typeof(CTest).GetCustomAttributes(true);

                      foreach( object att in atts )
                                  if( att is InspiredByAttribute )
                                                Console.WriteLine( "Class CTest was inspired by {0}",
    ((InspiredByAttribute)att).InspiredBy );
           }
    }

        41. 7.3 Can I create my own context attributes?

Yes. Take a look at Don Box's sample (called CallThreshold) at
http://www.develop.com/dbox/dotnet/threshold/, and also Peter Drayton's Tracehook.NET at
http://www.razorsoft.net/

8. Code Access Security

        42. 8.1 What is Code Access Security (CAS)?

CAS is the part of the .NET security model that determines whether or not a piece of code is allowed to run,
and what resources it can use when it is running. For example, it is CAS that will prevent a .NET web applet
from formatting your hard disk.

        43. 8.2 How does CAS work?

The CAS security policy revolves around two key concepts - code groups and permissions. Each .NET assembly
is a member of a particular code group, and each code group is granted the permissions specified in a
named permission set.

For example, using the default security policy, a control downloaded from a web site belongs to the 'Zone -
Internet' code group, which adheres to the permissions defined by the 'Internet' named permission set.
(Naturally the 'Internet' named permission set represents a very restrictive range of permissions.)

        44. 8.3 Who defines the CAS code groups?

Microsoft defines some default ones, but you can modify these and even create your own. To see the code
groups defined on your system, run 'caspol -lg' from the command-line. On my system it looks like this:

    Level = Machine

    Code Groups:

    1. All code: Nothing
      1.1. Zone - MyComputer: FullTrust
        1.1.1. Honor SkipVerification requests: SkipVerification
      1.2. Zone - Intranet: LocalIntranet
      1.3. Zone - Internet: Internet
      1.4. Zone - Untrusted: Nothing
      1.5. Zone - Trusted: Internet
      1.6. StrongName - 0024000004800000940000000602000000240000525341310004000003
    000000CFCB3291AA715FE99D40D49040336F9056D7886FED46775BC7BB5430BA4444FEF8348EBD06
    F962F39776AE4DC3B7B04A7FE6F49F25F740423EBF2C0B89698D8D08AC48D69CED0FC8F83B465E08
    07AC11EC1DCC7D054E807A43336DDE408A5393A48556123272CEEEE72F1660B71927D38561AABF5C
    AC1DF1734633C602F8F2D5: Everything

Note the hierarchy of code groups - the top of the hierarchy is the most general ('All code'), which is then sub-
divided into several groups, each of which in turn can be sub-divided. Also note that (somewhat counter-
intuitively) a sub-group can be associated with a more permissive permission set than its parent.

        45. 8.4 How do I define my own code group?

Use caspol. For example, suppose you trust code from www.mydomain.com and you want it have full access to
your system, but you want to keep the default restrictions for all other internet sites. To achieve this, you
would add a new code group as a sub-group of the 'Zone - Internet' group, like this:

    caspol -ag 1.3 -site www.mydomain.com FullTrust
Now if you run caspol -lg you will see that the new group has been added as group 1.3.1:

    ...
       1.3. Zone - Internet: Internet
         1.3.1. Site - www.mydomain.com: FullTrust
    ...

Note that the numeric label (1.3.1) is just a caspol invention to make the code groups easy to manipulate from
the command-line. The underlying runtime never sees it.

       46. 8.5 How do I change the permission set for a code group?

Use caspol. If you are the machine administrator, you can operate at the 'machine' level - which means not
only that the changes you make become the default for the machine, but also that users cannot change the
permissions to be more permissive. If you are a normal (non-admin) user you can still modify the permissions,
but only to make them more restrictive. For example, to allow intranet code to do what it likes you might do
this:

    caspol -cg 1.2 FullTrust

Note that because this is more permissive than the default policy (on a standard system), you should only do
this at the machine level - doing it at the user level will have no effect.

       47. 8.6 Can I create my own permission set?

Yes. Use caspol -ap, specifying an XML file containing the permissions in the permission set. To save you some
time, here is a sample file corresponding to the 'Everything' permission set - just edit to suit your needs. When
you have edited the sample, add it to the range of available permission sets like this:

    caspol -ap samplepermset.xml

Then, to apply the permission set to a code group, do something like this:

    caspol -cg 1.3 SamplePermSet

(By default, 1.3 is the 'Internet' code group)

       48. 8.7 I'm having some trouble with CAS. How can I diagnose my problem?

Caspol has a couple of options that might help. First, you can ask caspol to tell you what code group an
assembly belongs to, using caspol -rsg. Similarly, you can ask what permissions are being applied to a
particular assembly using caspol -rsp.

       49. 8.8 I can't be bothered with all this CAS stuff. Can I turn it off?

Yes, as long as you are an administrator. Just run:

    caspol -s off

9. Intermediate Language (IL)

       50. 9.1 Can I look at the IL for an assembly?

Yes. MS supply a tool called Ildasm which can be used to view the metadata and IL for an assembly.
       51. 9.2 Can source code be reverse-engineered from IL?

Yes, it is often relatively straightforward to regenerate high-level source (e.g. C#) from IL.

       52. 9.3 How can I stop my code being reverse-engineered from IL?

There is currently no simple way to stop code being reverse-engineered from IL. In future it is likely that IL
obfuscation tools will become available, either from MS or from third parties. These tools work by 'optimising'
the IL in such a way that reverse-engineering becomes much more difficult.

Of course if you are writing web services then reverse-engineering is not a problem as clients do not have
access to your IL.

       53. 9.4 Can I write IL programs directly?

Yes. Peter Drayton posted this simple example to the DOTNET mailing list:

    .assembly MyAssembly {}
    .class MyApp {
      .method static void Main() {
        .entrypoint
        ldstr   "Hello, IL!"
        call    void System.Console::WriteLine(class System.Object)
        ret
      }
    }

Just put this into a file called hello.il, and then run ilasm hello.il. An exe assembly will be generated.

       54. 9.5 Can I do things in IL that I can't do in C#?

Yes. A couple of simple examples are that you can throw exceptions that are not derived from
System.Exception, and you can have non-zero-based arrays.

10. Implications for COM

       55. 10.1 Is COM dead?

This subject causes a lot of controversy, as you'll see if you read the mailing list archives. Take a look at the
following two threads:

http://discuss.develop.com/archives/wa.exe?A2=ind0007&L=DOTNET&D=0&P=68241
http://discuss.develop.com/archives/wa.exe?A2=ind0007&L=DOTNET&P=R60761

FWIW my view is as follows: COM is many things, and it's different things to different people. But to me, COM
is fundamentally about how little blobs of code find other little blobs of code, and how they communicate with
each other when they find each other. COM specifies precisely how this location and communication takes
place. In a 'pure' .NET world, consisting entirely of .NET objects, little blobs of code still find each other and
talk to each other, but they don't use COM to do so. They use a model which is similar to COM in some ways -
for example, type information is stored in a tabular form packaged with the component, which is quite similar
to packaging a type library with a COM component. But it's not COM.

So, does this matter? Well, I don't really care about most of the COM stuff going away - I don't care that
finding components doesn't involve a trip to the registry, or that I don't use IDL to define my interfaces. But
there is one thing that I wouldn't like to go away - I wouldn't like to lose the idea of interface-based
development. COM's greatest strength, in my opinion, is its insistence on a cast-iron separation between
interface and implementation. Unfortunately, the .NET framework seems to make no such insistence - it lets
you do interface-based development, but it doesn't insist. Some people would argue that having a choice can
never be a bad thing, and maybe they're right, but I can't help feeling that maybe it's a backward step.
        56. 10.2 Is DCOM dead?

Pretty much, for .NET developers. The .NET Framework has a new remoting model which is not based on
DCOM. Of course DCOM will still be used in interop scenarios.

        57. 10.3 Is MTS/COM+ dead?

No. The approach for the first .NET release is to provide access to the existing COM+ services (through an
interop layer) rather than replace the services with native .NET ones. Various tools and attributes are provided
to try to make this as painless as possible. The PDC release of the .NET SDK includes interop support for core
services (JIT activation, transactions) but not some of the higher level services (e.g. COM+ Events, Queued
components).

Over time it is expected that interop will become more seamless - this may mean that some services become a
core part of the CLR, and/or it may mean that some services will be rewritten as managed code which runs on
top of the CLR.

For more on this topic, search for postings by Joe Long in the archives - Joe is the MS group manager for
COM+. Start with this message:

http://discuss.develop.com/archives/wa.exe?A2=ind0007&L=DOTNET&P=R68370

        58. 10.4 Can I use COM components from .NET programs?

Yes. COM components are accessed from the .NET runtime via a Runtime Callable Wrapper (RCW). This
wrapper turns the COM interfaces exposed by the COM component into .NET-compatible interfaces. For
oleautomation interfaces, the RCW can be generated automatically from a type library. For non-oleautomation
interfaces, it may be necessary to develop a custom RCW which manually maps the types exposed by the COM
interface to .NET-compatible types.

Here's a simple example for those familiar with ATL. First, create an ATL component which implements the
following IDL:

    import "oaidl.idl";
    import "ocidl.idl";

    [
           object,
           uuid(EA013F93-487A-4403-86EC-FD9FEE5E6206),
           helpstring("ICppName Interface"),
           pointer_default(unique),
           oleautomation
    ]

    interface ICppName : IUnknown
    {
           [helpstring("method SetName")] HRESULT SetName([in] BSTR name);
           [helpstring("method GetName")] HRESULT GetName([out,retval] BSTR *pName );
    };

    [
           uuid(F5E4C61D-D93A-4295-A4B4-2453D4A4484D),
           version(1.0),
           helpstring("cppcomserver 1.0 Type Library")
    ]
    library CPPCOMSERVERLib
    {
            importlib("stdole32.tlb");
            importlib("stdole2.tlb");
            [
                        uuid(600CE6D9-5ED7-4B4D-BB49-E8D5D5096F70),
                        helpstring("CppName Class")
            ]
            coclass CppName
            {
                       [default] interface ICppName;
            };
    };

When you've built the component, you should get a typelibrary. Run the TLBIMP utility on the typelibary, like
this:

    tlbimp cppcomserver.tlb

If successful, you will get a message like this:

    Typelib imported successfully to CPPCOMSERVERLib.dll

You now need a .NET client - let's use C#. Create a .cs file containing the following code:

    using System;
    using CPPCOMSERVERLib;

    public class MainApp
    {
           static public void Main()
           {
                       CppName cppname = new CppName();
                       cppname.SetName( "bob" );
                       Console.WriteLine( "Name is " + cppname.GetName() );
           }
    }

Note that we are using the type library name as a namespace, and the COM class name as the class.
Alternatively we could have used CPPCOMSERVERLib.CppName for the class name and gone without the using
CPPCOMSERVERLib statement.

Compile the C# code like this:

    csc /r:cppcomserverlib.dll csharpcomclient.cs

Note that the compiler is being told to reference the DLL we previously generated from the typelibrary using
TLBIMP.

You should now be able to run csharpcomclient.exe, and get the following output on the console:

    Name is bob

         59. 10.5 Can I use .NET components from COM programs?

Yes. .NET components are accessed from COM via a COM Callable Wrapper (CCW). This is similar to a RCW
(see previous question), but works in the opposite direction. Again, if the wrapper cannot be automatically
generated by the .NET development tools, or if the automatic behaviour is not desirable, a custom CCW can be
developed. Also, for COM to 'see' the .NET component, the .NET component must be registered in the registry.

Here's a simple example. Create a C# file called testcomserver.cs and put the following in it:



    using System;

    namespace AndyMc
    {
            [ClassInterface(ClassInterfaceType.AutoDual)]
            public class CSharpCOMServer
            {
                        public CSharpCOMServer() {}
                        public void SetName( string name ) { m_name = name; }
                        public string GetName() { return m_name; }
                        private string m_name;
            }
    }

Then compile the .cs file as follows:

    csc /target:library testcomserver.cs

You should get a dll, which you register like this:

    regasm testcomserver.dll /tlb:testcomserver.tlb /codebase

Now you need to create a client to test your .NET COM component. VBScript will do - put the following in a file
called comclient.vbs:

    Dim dotNetObj
    Set dotNetObj = CreateObject("AndyMc.CSharpCOMServer")
    dotNetObj.SetName ("bob")
    MsgBox "Name is " & dotNetObj.GetName()

and run the script like this:

    wscript comclient.vbs

And hey presto you should get a message box displayed with the text "Name is bob".

An alternative to the approach above it to use the dm.net moniker developed by Jason Whittington and Don
Box. Go to http://staff.develop.com/jasonw/clr/readme.htm to check it out.

        60. 10.6 Is ATL redundant in the .NET world?

Yes, if you are writing applications that live inside the .NET framework. Of course many developers may wish
to continue using ATL to write C++ COM components that live outside the framework, but if you are inside you
will almost certainly want to use C#. Raw C++ (and therefore ATL which is based on it) doesn't have much of
a place in the .NET world - it's just too near the metal and provides too much flexibility for the runtime to be
able to manage it.

11. Miscellaneous

        61. 11.1 How does .NET remoting work?

.NET remoting involves sending messages along channels. Two of the standard channels are HTTP and TCP.
TCP is intended for LANs only - HTTP can be used for LANs or WANs (internet).

Support is provided for multiple message serializarion formats. Examples are SOAP (XML-based) and binary.
By default, the HTTP channel uses SOAP (via the .NET runtime Serialization SOAP Formatter), and the TCP
channel uses binary (via the .NET runtime Serialization Binary Formatter). But either channel can use either
serialization format.

There are a number of styles of remote access:
        SingleCall. Each incoming request from a client is serviced by a new object. The object is thrown away
         when the request has finished.


        Singleton. All incoming requests from clients are processed by a single server object.


        Client-activated object. This is the old stateful (D)COM model whereby the client receives a reference
         to the remote object and holds that reference (thus keeping the remote object alive) until it is
         finished with it.

Distributed garbage collection of objects is managed by a system called 'leased based lifetime'. Each object
has a lease time, and when that time expires the object is disconnected from the .NET runtime remoting
infrastructure. Objects have a default renew time - the lease is renewed when a successful call is made from
the client to the object. The client can also explicitly renew the lease.

If you're interested in using XML-RPC as an alternative to SOAP, take a look at Charles Cook's XML-RPC.Net
site at http://www.cookcomputing.com/xmlrpc/xmlrpc.shtml.

        62. 11.2 How can I get at the Win32 API from a .NET program?

Use P/Invoke. This uses similar technology to COM Interop, but is used to access static DLL entry points
instead of COM objects. Here is an example of C# calling the Win32 MessageBox function:

    using System;
    using System.Runtime.InteropServices;

    class MainApp
    {
           [DllImport("user32.dll", EntryPoint="MessageBox", SetLastError=true, CharSet=CharSet.Auto)]
           public static extern int MessageBox(int hWnd, String strMessage, String strCaption, uint uiType);

           public static void Main()
           {
                       MessageBox( 0, "Hello, this is PInvoke in operation!", ".NET", 0 );
           }
    }

12. Class Library

        63. 12.1 File I/O



  12.1.1 How do I read from a text file?

First, use a System.IO.FileStream object to open the file:

    FileStream fs = new FileStream( @"c:\test.txt", FileMode.Open, FileAccess.Read );

FileStream inherits from Stream, so you can wrap the FileStream object with a StreamReader object. This
provides a nice interface for processing the stream line by line:

    StreamReader sr = new StreamReader( fs );
    string curLine;
    while( (curLine = sr.ReadLine()) != null )
           Console.WriteLine( curLine );

Finally close the StreamReader object:

    sr.Close();
Note that this will automatically call Close() on the underlying Stream object, so an explicit fs.Close() is not
required.



  12.1.2 How do I write to a text file?

Similar to the read example, except use StreamWriter instead of StreamReader.



  12.1.3 How do I read/write binary files?

Similar to text files, except wrap the FileStream object with a BinaryReader/Writer object instead of a
StreamReader/Writer object.

       64. 12.2 Text Processing



  12.2.1 Are regular expressions supported?

Yes. Use the System.Text.RegularExpressions.Regex class. For example, the following code updates the title in
an HTML file:

    FileStream fs = new FileStream( "test.htm", FileMode.Open, FileAccess.Read );
    StreamReader sr = new StreamReader( fs );

    Regex r = new Regex( "<TITLE>(.*)</TITLE>" );
    string s;
    while( (s = sr.ReadLine()) != null )
    {
           if( r.IsMatch( s ) )
                       s = r.Replace( s, "<TITLE>New and improved ${1}</TITLE>" );
           Console.WriteLine( s );
    }

       65. 12.3 Internet



  12.3.1 How do I download a web page?

First use the System.Net.WebRequestFactory class to acquire a WebRequest object:

    WebRequest request = WebRequest.Create( "http://localhost" );

Then ask for the response from the request:

    WebResponse response = request.GetResponse();

The GetResponse method blocks until the download is complete. Then you can access the response stream like
this:

    Stream s = response.GetResponseStream();

    // Output the downloaded stream to the console
    StreamReader sr = new StreamReader( s );
    string line;
    while( (line = sr.ReadLine()) != null )
            Console.WriteLine( line );
Note that WebRequest and WebReponse objects can be downcast to HttpWebRequest and HttpWebReponse
objects respectively, to access http-specific functionality.



  12.3.2 How do I use a proxy?

Two approaches - to affect all web requests do this:

    System.Net.GlobalProxySelection.Select = new WebProxy( "proxyname", 80 );

Alternatively, to set the proxy for a specific web request, do this:

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create( "http://localhost" );
    request.Proxy = new WebProxy( "proxyname", 80 );

       66. 12.4 XML



  12.4.1 Is DOM supported?

Yes. Take this example XML document:

    <PEOPLE>
         <PERSON>Fred</PERSON>
         <PERSON>Bill</PERSON>
    </PEOPLE>

This document can be parsed as follows:

    XmlDocument doc = new XmlDocument();
    doc.Load( "test.xml" );

    XmlNode root = doc.DocumentElement;

    foreach( XmlNode personElement in root.ChildNodes )
           Console.WriteLine( personElement.FirstChild.Value.ToString() );

The output is:

    Fred
    Bill




  12.4.2 Is SAX supported?

No. Instead, a new XmlReader/XmlWriter API is offered. Like SAX it is stream-based but it uses a 'pull' model
rather than SAX's 'push' model. Here's an example:

    XmlTextReader reader = new XmlTextReader( "test.xml" );

    while( reader.Read() )
    {
           if( reader.NodeType == XmlNodeType.Element && reader.Name == "PERSON" )
           {
                      reader.Read(); // Skip to the child text
                      Console.WriteLine( reader.Value );
           }
    }



  12.4.3 Is XPath supported?

Yes, via the XPathXXX classes:

    XPathDocument xpdoc = new XPathDocument("test.xml");
    XPathNavigator nav = xpdoc.CreateNavigator();
    XPathExpression expr = nav.Compile("descendant::PEOPLE/PERSON");

    XPathNodeIterator iterator = nav.Select(expr);
    while (iterator.MoveNext())
           Console.WriteLine(iterator.Current);

        67. 12.5 Threading



  12.5.1 Is multi-threading supported?

Yes, there is extensive support for multi-threading. New threads can be spawned, and there is a system-
provided threadpool which applications can use.



  12.5.2 How do I spawn a thread?

Create an instance of a System.Threading.Thread object, passing it an instance of a ThreadStart delegate that
will be executed on the new thread. For example:

    class MyThread
    {
           public MyThread( string initData )
           {
                      m_data = initData;
                      m_thread = new Thread( new ThreadStart(ThreadMain) );
                      m_thread.Start();
           }

           // ThreadMain() is executed on the new thread.
           private void ThreadMain()
           {
                       Console.WriteLine( m_data );
           }

           public void WaitUntilFinished()
           {
                       m_thread.Join();
           }

           private Thread m_thread;
           private string m_data;
    }

In this case creating an instance of the MyThread class is sufficient to spawn the thread and execute the
MyThread.ThreadMain() method:
    MyThread t = new MyThread( "Hello, world." );
    t.WaitUntilFinished();



  12.5.3 How do I stop a thread?

There are several options. First, you can use your own communication mechanism to tell the ThreadStart
method to finish. Alternatively the Thread class has in-built support for instructing the thread to stop. The two
principle methods are Thread.Interrupt() and Thread.Abort(). The former will cause a
ThreadInterruptedException to be thrown on the thread when it next goes into a WaitJoinSleep state. In other
words, Thread.Interrupt is a polite way of asking the thread to stop when it is no longer doing any useful work.
In contrast, Thread.Abort() throws a ThreadAbortException regardless of what the thread is doing.
Furthermore, the ThreadAbortException cannot normally be caught (though the ThreadStart's finally method
will be executed). Thread.Abort() is a heavy-handed mechanism which should not normally be required.



  12.5.4 How do I use the thread pool?

By passing an instance of a WaitCallback delegate to the ThreadPool.QueueUserWorkItem() method:

    class CApp
    {
           static void Main()
           {
                       string s = "Hello, World";
                       ThreadPool.QueueUserWorkItem( new WaitCallback( DoWork ), s );

                       Thread.Sleep( 1000 ); // Give time for work item to be executed
           }

           // DoWork is executed on a thread from the thread pool.
           static void DoWork( object state )
           {
                       Console.WriteLine( state );
           }
    }



  12.5.5 How do I know when my thread pool work item has completed?

There is no way to query the thread pool for this information. You must put code into the WaitCallback method
to signal that it has completed. Events are useful for this.



  12.5.6 How do I prevent concurrent access to my data?

Each object has a concurrency lock (critical section) associated with it. The
System.Threading.Monitor.Enter/Exit methods are used to acquire and release this lock. For example,
instances of the following class only allow one thread at a time to enter method f():

    class C
    {
           public void f()
           {
                       try
                       {
                                  Monitor.Enter(this);
                                  ...
                       }
                       finally
                       {
                                    Monitor.Exit(this);
                       }
           }
    }

C# has a 'lock' keyword which provides a convenient shorthand for the code above:

    class C
    {
           public void f()
           {
                       lock(this)
                       {
                                    ...
                       }
           }
    }

Note that calling Monitor.Enter(myObject) does NOT mean that all access to myObject is serialized. It means
that the synchronisation lock associated with myObject has been acquired, and no other thread can acquire
that lock until Monitor.Exit(o) is called. In other words, this class is functionally equivalent to the classes
above:

    class C
    {
           public void f()
           {
                       lock( m_object )
                       {
                                 ...
                       }
           }

           private m_object = new object();
    }

        68. 12.6 Tracing



  12.6.1 Is there built-in support for tracing/logging?

Yes, in the System.Diagnostics namespace. There are two main classes that deal with tracing - Debug and
Trace. They both work in a similar way - the difference is that tracing from the Debug class only works in
builds that have the DEBUG symbol defined, whereas tracing from the Trace class only works in builds that
have the TRACE symbol defined. Typically this means that you should use System.Diagnostics.Trace.WriteLine
for tracing that you want to work in debug and release builds, and System.Diagnostics.Debug.WriteLine for
tracing that you want to work only in debug builds.




  12.6.2 Can I redirect tracing to a file?

Yes. The Debug and Trace classes both have a Listeners property, which is a collection of sinks that receive the
tracing that you send via Debug.WriteLine and Trace.WriteLine respectively. By default the Listeners collection
contains a single sink, which is an instance of the DefaultTraceListener class. This sends output to the Win32
OutputDebugString() function and also the System.Diagnostics.Debugger.Log() method. This is useful when
debugging, but if you're trying to trace a problem at a customer site, redirecting the output to a file is more
appropriate. Fortunately, the TextWriterTraceListener class is provided for this purpose.

Here's how to use the TextWriterTraceListener class to redirect Trace output to a file:

    Trace.Listeners.Clear();
    FileStream fs = new FileStream( @"c:\log.txt", FileMode.Create, FileAccess.Write );
    Trace.Listeners.Add( new TextWriterTraceListener( fs ) );

    Trace.WriteLine( @"This will be writen to c:\log.txt!" );
    Trace.Flush();

Note the use of Trace.Listeners.Clear() to remove the default listener. If you don't do this, the output will go to
the file and OutputDebugString(). Typically this is not what you want, because OutputDebugString() imposes a
big performance hit.



  12.6.3 Can I customise the trace output?

Yes. You can write your own TraceListener-derived class, and direct all output through it. Here's a simple
example, which derives from TextWriterTraceListener (and therefore has in-built support for writing to files, as
shown above) and adds timing information and the thread ID for each trace line:

    class MyListener : TextWriterTraceListener
    {
           public MyListener( Stream s ) : base(s)
           {
           }

           public override void WriteLine( string s )
           {
                      Writer.WriteLine( "{0:D8} [{1:D4}] {2}",
                                  Environment.TickCount - m_startTickCount,
                                  AppDomain.GetCurrentThreadId(),
                                  s );
           }

           protected int m_startTickCount = Environment.TickCount;
    }

(Note that this implementation is not complete - the TraceListener.Write method is not overridden for
example.)

The beauty of this approach is that when an instance of MyListener is added to the Trace.Listeners collection,
all calls to Trace.WriteLine() go through MyListener, including calls made by referenced assemblies that know
nothing about the MyListener class.

                13 Recommended books

I recommend the following books, either because I personally like them, or because I think they are well
regarded by other .NET developers. (Note that I get a commission from Amazon if you buy a book after
following one of these links.)


        Applied Microsoft .NET Framework Programming - Jeffrey Richter
         Much anticipated, mainly due to Richter's superb Win32 books, and most people think it delivers. The
         'applied' is a little misleading - this book is mostly about how the .NET Framework works 'under the
         hood'. Examples are in C#, but there is also a separate VB edition of the book.


        Essential .NET Volume 1, The Common Language Runtime - Don Box
         Don's books don't always demonstrate the same dazzling ability to communicate that he exhibits in
         person, but they are always chock full of technical detail you just don't get other places. Essential
         .NET is likely to become a must-read for all .NET developers.


        Programming Windows with C# - Charles Petzold
         Another slightly misleading title - this book is solely about GUI programming - Windows Forms and
         GDI+. Well written, with comprehensive coverage. My only (minor) criticism is that the book sticks




                               ASP.NET Interview Questions

1.       Describe the role of inetinfo.exe, aspnet_isapi.dll and aspnet_wp.exe in the page loading
process ?
Ans : inetinfo.exe is the Microsoft IIS server running, handling ASP.NET requests among other things. When an
ASP.NET request is received (usually a file with .aspx extension), the ISAPI filter aspnet_isapi.dll takes care of
it by passing the request to the actual worker process aspnet_wp.exe.

2. What’s the difference between Response.Write() and Response.Output.Write()?
Ans : Response.Output.Write() allows you to write formatted output.

3. What methods are fired during the page load?
Ans : Init() - when the page is instantiated
Load() - when the page is loaded into server memory
PreRender() - the brief moment before the page is displayed to the user as HTML
Unload() - when page finishes loading.

4. When during the page processing cycle is ViewState available?
Ans : After the Init() and before the Page_Load(), or OnLoad() for a control.

5. What namespace does the Web page belong in the .NET Framework class hierarchy?
Ans : System.Web.UI.Page

6. Where do you store the information about the user’s locale?
Ans : System.Web.UI.Page.Culture

7. What’s the difference between Codebehind="MyCode.aspx.cs" and Src="MyCode.aspx.cs"?
Ans : CodeBehind is relevant to Visual Studio.NET only.

8. What’s a bubbled event?
Ans : When you have a complex control, like DataGrid, writing an event processing routine for each object
(cell, button, row, etc.) is quite tedious. The controls can bubble up their event handlers, allowing the main
DataGrid event handler to take care of its constituents.

9. Suppose you want a certain ASP.NET function executed on MouseOver for a certain button.
Where do you add an event handler?
Ans     :       Add       an    OnMouseOver        attribute     to the button.   Example:
btnSubmit.Attributes.Add("onmouseover","someClientCodeHere();");

10. What data types do the RangeValidator control support?
Ans : Integer, String, and Date.

11. Explain the differences between Server-side and Client-side code?
Ans : Server-side code executes on the server. Client-side code executes in the client's browser.

12. What type of code (server or client) is found in a Code-Behind class?
Ans : The answer is server-side code since code-behind is executed on the server. However, during the code-
behind's execution on the server, it can render client-side code such as JavaScript to be processed in the
clients browser. But just to be clear, code-behind executes on the server, thus making it server-side code.

13. Should user input data validation occur server-side or client-side? Why?
Ans : All user input data validation should occur on the server at a minimum. Additionally, client-side
validation can be performed where deemed appropriate and feasable to provide a richer, more responsive
experience for the user.
14. What is the difference between Server.Transfer and Response.Redirect? Why would I choose
one over the other?
Ans : Server.Transfer transfers page processing from one page directly to the next page without making a
round-trip back to the client's browser. This provides a faster response with a little less overhead on the
server. Server.Transfer does not update the clients url history list or current url. Response.Redirect is used to
redirect the user's browser to another page or site. This perform as a trip back to the client where the client's
browser is redirected to the new page. The user's browser history list is updated to reflect the new address.



15. Can you explain the difference between an ADO.NET Dataset and an ADO Recordset?
Valid answers are:
· A DataSet can represent an entire relational database in memory, complete with tables, relations, and views.
· A DataSet is designed to work without any continuing connection to the original data source.
· Data in a DataSet is bulk-loaded, rather than being loaded on demand.
· There's no concept of cursor types in a DataSet.
· DataSets have no current record pointer You can use For Each loops to move through the data.
· You can store many edits in a DataSet, and write them to the original data source in a single operation.
· Though the DataSet is universal, other objects in ADO.NET come in different versions for different data
sources.

16. What is the Global.asax used for?
Ans : The Global.asax (including the Global.asax.cs file) is used to implement application and session level
events.

17. What are the Application_Start and Session_Start subroutines used for?
Ans : This is where you can set the specific variables for the Application and Session objects.

18. Can you explain what inheritance is and an example of when you might use it?
Ans : When you want to inherit (use the functionality of) another class. Example: With a base class named
Employee, a Manager class could be derived from the Employee base class.

19. Whats an assembly?
Ans : Assemblies are the building blocks of the .NET framework.

20. Describe the difference between inline and code behind.
Ans : Inline code written along side the html in a page. Code-behind is code written in a separate file and
referenced by the .aspx page.

21. Explain what a diffgram is, and a good use for one?
Ans : The DiffGram is one of the two XML formats that you can use to render DataSet object contents to XML.
A good use is reading database data to an XML file to be sent to a Web Service.

22. Whats MSIL, and why should my developers need an appreciation of it if at all?
Ans : MSIL is the Microsoft Intermediate Language. All .NET compatible languages will get converted to MSIL.
MSIL also allows the .NET Framework to JIT compile the assembly on the installed computer.


23. Which method do you invoke on the DataAdapter control to load your generated dataset with
data?
Ans : The Fill() method.

24. Can you edit data in the Repeater control?
Ans : No, it just reads the information from its data source.

25. Which template must you provide, in order to display data in a Repeater control?
Ans : ItemTemplate.

26. How can you provide an alternating color scheme in a Repeater control?
Ans : Use the AlternatingItemTemplate.

27. What property must you set, and what method must you call in your code, in order to bind the
data from a data source to the Repeater control?
Ans : You must set the DataSource property and call the DataBind method.
28. What base class do all Web Forms inherit from?
Ans : The Page class.

29. Name two properties common in every validation control?
Ans : ControlToValidate property and Text property.

30. Which property on a Combo Box do you set with a column name, prior to setting the
DataSource, to display data in the combo box?
Ans : DataTextField property.

31. Which control would you use if you needed to make sure the values in two different controls
matched?
Ans : CompareValidator control.

32. How many classes can a single .NET DLL contain?
Ans : It can contain many classes.

33. What is ViewState?
Ans : ViewState allows the state of objects (serializable) to be stored in a hidden field on the page. ViewState
is transported to the client and back to the server, and is not stored on the server or any other external
source. ViewState is used to retain the state of server-side objects between post backs.

34. What is the lifespan for items stored in ViewState?
Ans : Item stored in ViewState exist for the life of the current page. This includes postbacks (to the same
page).

35. What does the "EnableViewState" property do? Why would I want it on or off?
Ans : It allows the page to save the users input on a form across postbacks. It saves the server-side values
for a given control into ViewState, which is stored as a hidden value on the page before sending the page to
the clients browser. When the page is posted back to the server the server control is recreated with the state
stored in viewstate.

36. What are the different types of Session state management options available with ASP.NET?
Ans : ASP.NET provides In-Process and Out-of-Process state management. In-Process stores the session in
memory on the web server. This requires the a "sticky-server" (or no load-balancing) so that the user is
always reconnected to the same web server. Out-of-Process Session state management stores data in an
external data source. The external data source may be either a SQL Server or a State Server service. Out-of-
Process state management requires that all objects stored in session are serializable.

37. What is CLS (Common Language Specificaiton)?
Ans : It provides the set of specificaiton which has to be adhered by any new language writer / Compiler writer
for .NET Framework. This ensures Interoperability. For example: Within a ASP.NET application written in
C#.NET language, we can refer to any DLL written in any other language supported by .NET Framework. As of
now .NET Supports around 32 languages.

38. What is CTS (Common Type System)?
Ans : It defines about how Objects should be declard, defined and used within .NET. CLS is the subset of CTS.
39. What is Boxing and UnBoxing?
Ans : Boxing is implicit conversion of ValueTypes to Reference Types (Object). UnBoxing is explicit conversion
of Reference Types (Object) to its equivalent ValueTypes. It requires type-casting.

40. What is the difference between Value Types and Reference Types?
Ans : Value Types uses Stack to store the data where as the later uses the Heap to store the data.

41. What are the different types of assemblies available and their purpose?
Ans : Private, Public/shared and Satellite Assemblies.
Private Assemblies : Assembly used within an application is known as private assemblies.
Public/shared Assemblies : Assembly which can be shared across applicaiton is known as shared assemblies.
Strong Name has to be created to create a shared assembly. This can be done using SN.EXE. The same has to
be             registered          using             GAC             Util.exe         (GlobalAssemblyCache).
Satellite Assemblies : These assemblies contain resource files pertaining to a locale (Culture+Language).
These assemblies are used in deploying an Gloabl applicaiton for different languages.

42. What is view state and use of it? The current property settings of an ASP.NET page and those of any
ASP.NET server controls contained within the page. ASP.NET can detect when a form is requested for the first
time versus when the form is posted (sent to the server), which allows you to program accordingly.
43.What are user control sand custom controls?



Custom controls: A control authored by a user or a third-party software vendor that does not belong to the
.NET Framework class library. This is a generic term that includes user controls. A custom server control is
used in Web Forms (ASP.NET pages). A custom client control is used in Windows Forms applications.

User Controls: In ASP.NET: A user-authored server control that enables an ASP.NET page to be re-used as
a server control. An ASP.NET user control is authored declaratively and persisted as a text file with an .ascx
extension. The ASP.NET page framework compiles a user control on the fly to a class that derives from the
System.Web.UI.UserControl class.

44. What are the validation controls?

A set of server controls included with ASP.NET that test user input in HTML and Web server controls for
programmer-defined requirements. Validation controls perform input checking in server code. If the user is
working with a browser that supports DHTML, the validation controls can also perform validation using client
script.

45.    What's     the   difference     between           Response.Write()       andResponse.Output.Write()?
Thelatteroneallowsyoutowriteformattedoutput.

46.     What         methods        are       fired      during        the     page      load?       Init()
 When the page is instantiated, Load() - when the page is loaded into server memory,PreRender () - the brief
moment before the page is displayed to the user as HTML, Unload() - when page finishes loading.

47. Where does           the   Web     page     belong     in   the   .NET    Framework   class     hierarchy?
System.Web.UI.Page

48.    Where     do      you         store      the      information        about   the    user's      locale?
System.Web.UI.Page.Culture

49. What's the difference between Codebehind="MyCode.aspx.cs" and Src="MyCode.aspx.cs"?
CodeBehind is relevant to Visual Studio.NET only.

 What's a bubbled event?                                                                                 When
you have a complex control, likeDataGrid, writing an event processing routine for each object (cell,
button,row, etc.) is quite tedious. The controls can bubble up their eventhandlers, allowing the main DataGrid
event handler to take care of its constituents. Suppose you want a certain ASP.NET function executed on
MouseOver over a certain button.

51. Where do you add an event handler?

 It's the Attributesproperty, the Add function inside that property. e.g.
btnSubmit.Attributes.Add("onMouseOver","someClientCode();")

52. What data type does the RangeValidator control support?
Integer,String and Date.




53. What are the different types of caching?

Caching is a technique widely used in computing to increase performance by keeping frequently accessed or
expensive data in memory. In context of web application, caching is used to retain the pages or data across
HTTP requests and reuse them without the expense of recreating them. ASP.NET has 3 kinds of caching
strategies Output Caching, Fragment Caching, Data Caching.
Output Caching: Caches the dynamic output generated by a request. Some times it is useful to cache the
output of a website even for a minute, which will result in a better performance. For caching the whole page
the page should have OutputCache directive.<%@ OutputCache Duration="60" VaryByParam="state" %>

Fragment Caching: Caches the portion of the page generated by the request. Some times it is not practical
to cache the entire page, in such cases we can cache a portion of page<%@ OutputCache Duration="120"
VaryByParam="CategoryID;SelectedID"%>

Data Caching: Caches the objects programmatically. For      data caching asp.net provides a cache object for
eg:cache["States"]=dsStates;




54. What do you mean by authentication and authorization?

 Authentication is the process of validating a user on the credentials (username and          password) and
authorization performs after authentication. After Authentication a user will be verified for performing the
various tasks, Its access is limited it is known as  authorization.

55. What are different types of directives in .NET?

@Page: Defines page-specific attributes used by the ASP.NET page parser and compiler. Can       be included
only in .aspx files <%@ Page AspCompat="TRUE" language="C#" %>

@Control:Defines control-specific attributes used by the ASP.NET page parser and          compiler. Can be
included only in .ascx files. <%@ Control Language="VB" EnableViewState="false" %>



@Import: Explicitly imports a namespace into a page or user control. The Import      directive cannot have
more than one namespace attribute. To import multiple    namespaces,      use multiple @Import directives.
<% @ Import Namespace="System.web" %>

@Implements: Indicates that the current page or user control implements the specified .NET       framework
interface.<%@ Implements Interface="System.Web.UI.IPostBackEventHandler" %>

@Register: Associates aliases with namespaces and class names for concise notation in  custom server
control syntax.<%@ Register Tagprefix="Acme" Tagname="AdRotator" Src="AdRotator.ascx" %>

@Assembly: Links an assembly to the current page during compilation, making all the assembly's
classes and interfaces available for use on the    page.   <%@ Assembly Name="MyAssembly" %>
<%@Assembly Src="MySource.vb" %>

@OutputCache: Declaratively controls the output caching policies of an ASP.NET page or a  user control
contained in a page<%@ OutputCache Duration="#ofseconds" Location="Any | Client | Downstream | Server
| None" Shared="True | False" VaryByControl="controlname" VaryByCustom="browser | customstring"
VaryByHeader="headers" VaryByParam="parametername" %>

@Reference: Declaratively indicates that another user control or page source file                 should be
dynamically compiled and linked against the page in which this directive is declared.

56. How do I debug an ASP.NET application that wasn't written with Visual Studio.NET and that
doesn't use code-behind?

Start the DbgClr debugger that comes with the .NET Framework SDK, open the file containing    the code you
want to debug, and set your breakpoints. Start the ASP.NET application. Go back to DbgClr, choose Debug
Processes from the Tools menu, and select aspnet_wp.exe from the list of processes. (If aspnet_wp.exe
doesn't appear in the list,check the "Show system     processes" box.) Click the Attach button to attach to
aspnet_wp.exe                                     and                                     begin debugging.
Be sure to enable debugging in the ASPX file before debugging it with DbgClr. You can enable tell ASP.NET to
build               debug               executables                  by               placing               a
<%@ Page Debug="true" %> statement at the top of an ASPX file or a <COMPILATION debug="true"
/>statement                     in                    a                    Web.config                   file.

57. Can a user browsing my Web site read my Web.config or Global.asax files? No. The
<HTTPHANDLERS>section of Machine.config, which holds the master configuration settings for ASP.NET,
contains entries that map ASAX files, CONFIG files, and selected other file types to an HTTP handler named
HttpForbiddenHandler, which fails attempts to retrieve the associated file. You can modify it by editing
Machine.config or including an section in a local Web.config file.

58. What's the difference between Page.RegisterClientScriptBlock and Page.RegisterStartupScript?
RegisterClientScriptBlock is for returning blocks of client-side script containing functions. RegisterStartupScript
is for returning blocks of client-script not packaged in functions-in other words, code that's to execute when
the page is loaded. The latter positions script blocks near the end of the document so elements on the
page that the script interacts are loaded before the script runs.<%@ Reference Control="MyControl.ascx" %>

59. Is it necessary to lock application state before accessing it?
Only if you're performing a multistep update and want the update to be treated as an atomic        operation.
Here's an example:
            Application.Lock ();
            Application["ItemsSold"] = (int) Application["ItemsSold"] + 1;
            Application["ItemsLeft"] = (int) Application["ItemsLeft"] - 1;
            Application.UnLock ();

By locking application state before updating it and unlocking it afterwards, you ensure that another request
being processed on another thread doesn't read application state at exactly the wrong time and see an
inconsistent view of it. If I update session state, should I lock it, too? Are concurrent accesses by multiple
requests executing on multiple threads a concern with session state? Concurrent accesses aren't an issue with
session state, for two reasons. One, it's unlikely that two requests from the same user will overlap. Two, if
they do overlap, ASP.NET locks down session state during request processing so that two threads can't touch it
at once. Session state is locked down when the HttpApplication instance that's processing the request fires an
AcquireRequestState event and unlocked when it fires a ReleaseRequestState event.

Do ASP.NET forms authentication cookies provide any protection against replay attacks? Do they, for example,
include the client's IP address or anything else that would distinguish the real client from an attacker?
No. If an authentication cookie is stolen, it can be used by an attacker. It's up to you to      prevent this from
happening by using an encrypted communications channel (HTTPS). Authentication cookies issued as session
cookies, do, however,include a time-out valid that      limits their lifetime. So a stolen session cookie can only
be used in replay attacks as long as the ticket inside the cookie is valid. The default time-out interval is 30
minutes.You can change that by modifying the timeout attribute accompanying the <forms> element in
Machine.config or a local Web.config file. Persistent authentication cookies do not time-out and therefore are a
more serious security threat if stolen.

60. How do I send e-mail from an ASP.NET application?

     MailMessage message = new MailMessage ();
     message.From = <email>;
     message.To = <email>;
     message.Subject = "Scheduled Power Outage";
     message.Body = "Our servers will be down tonight.";
     SmtpMail.SmtpServer = "localhost";
     SmtpMail.Send (message);

 MailMessage and SmtpMail are classes defined in the .NET Framework Class Library's System.Web.Mail
namespace. Due to a security change made to ASP.NET just before it shipped, you need to set SmtpMail's
SmtpServer property to "localhost" even though "localhost" is the default. In addition, you must use the IIS
configuration applet to enable localhost (127.0.0.1) to relay messages through the local SMTP service.

61. What are VSDISCO files? VSDISCO files are DISCO files that support dynamic discovery of Web
services. If you place the following VSDISCO file in a directory on your Web server, for example, it returns
references to all ASMX and DISCO files in the host directory and any subdirectories not noted in <exclude>
elements:
         <?xml version="1.0" ?>
          <dynamicDiscovery
            xmlns="urn:schemas-dynamicdiscovery:disco.2000-03-17">
            <exclude path="_vti_cnf" />
            <exclude path="_vti_pvt" />
            <exclude path="_vti_log" />
            <exclude path="_vti_script" />
            <exclude path="_vti_txt" />
          </dynamicDiscovery>

62. How does dynamic discovery work? ASP.NET maps the file name extension VSDISCO to an HTTP
handler that scans the host directory and subdirectories for ASMX and DISCO files and returns a dynamically
generated DISCO document. A client who requests a VSDISCO file gets back what appears to be a static
DISCO                                                                                            document.
Note that VSDISCO files are disabled in the release version of ASP.NET. You can reenable them by
uncommenting the line       in the <httpHandlers> section of Machine.config that maps *.vsdisco to
System.Web.Services.Discovery.DiscoveryRequestHandler and granting the ASPNET user account permission
to read the IIS metabase. However, Microsoft is actively discouraging the use of VSDISCO files because they
could          represent         a          threat          to         Web          server         security.

63. Is it possible to prevent a browser from caching an ASPX page? Just call SetNoStore on the
HttpCachePolicy object exposed through the Response object's Cache property, as demonstrated here:



     <%@ Page Language="C#" %>
     <html>
      <body>
       <%
         Response.Cache.SetNoStore ();
         Response.Write (DateTime.Now.ToLongTimeString ());
       %>
      </body>
     </html>

SetNoStore works by returning a Cache-Control: private, no-store header in the HTTP response. In this
example, it prevents caching of a Web page that shows the current time.

64.     What       does     AspCompat="true"        mean       and     when       should      I     use      it?
AspCompat is an aid in migrating ASP pages to ASPX pages. It defaults to false but should be set to true in any
ASPX    file   that   creates apartment-threaded      COM objects--that      is,   COM objects       registered
ThreadingModel=Apartment. That includes all COM objects written with Visual Basic 6.0. AspCompat should
also be set to true (regardless of threading model) if the page creates COM objects that access intrinsic ASP
objects such as Request and Response. The following directive sets AspCompat to true:

      <%@ Page AspCompat="true" %>

Setting AspCompat to true does two things. First, it makes intrinsic ASP objects available   to the COM
components by placing unmanaged wrappers around the equivalent ASP.NET objects. Second, it improves the
performance of calls that the page places to apartment- threaded COM objects by ensuring that the page
(actually, the thread that processes the request for the page) and the COM objects it creates share an
apartment. AspCompat="true" forces ASP.NET request threads into single-threaded apartments (STAs). If
those threads create COM objects marked ThreadingModel=Apartment, then the objects are created in the
same STAs as the threads that created them. Without AspCompat="true," request threads run in a
multithreaded apartment (MTA) and each call to an STA-based COM object incurs a performance hit when it's
marshaled across apartment boundaries.

Do not set AspCompat to true if your page uses no COM objects or if it uses COM objects that don't access ASP
intrinsic objects and that are registered ThreadingModel=Free or ThreadingModel=Both.

65.     Explain       the    differences        between        Server-side      and      Client-side    code?
 Server side scripting means that all the script will be executed by the server and interpreted as needed. ASP
doesn't have some of the functionality like sockets, uploading, etc. For these you have to make a custom
components usually in VB or VC++. Client side scripting means that the script will be executed immediately in
the browser such as form field validation, clock, email validation, etc. Client side scripting is usually done in
VBScript or JavaScript. Download time, browser compatibility, and visible code - since JavaScript and VBScript
code is included in the HTML page, then anyone can see the code by viewing the page source. Also a possible
security hazards for the client computer.

66. What type of code (server or client) is found in a Code-Behind class?
C#

67. Should validation (did the user enter a real date) occur server-side or client-side? Why?
Client-side validation because there is no need to request a server side date when you could obtain a date
from the client machine.

68. What are ASP.NET Web Forms? How is this technology different than what is available though
ASP?
Web Forms are the heart and soul of ASP.NET. Web Forms are the User Interface (UI) elements that give your
Web applications their look and feel. Web Forms are similar to Windows Forms in that they provide properties,
methods, and events for the controls that are placed onto them. However, these UI elements render
themselves in the appropriate markup language required by the request, e.g. HTML. If you use Microsoft
Visual Studio .NET, you will also get the familiar drag-and-drop interface used to create your UI for your Web
application.

69. What is the difference between Server.Transfer and Response.Redirect? Why would I choose
one                                 over                                 the                             other?
In earlier versions of IIS, if we wanted to send a user to a new Web page, the only option we had was
Response.Redirect. While this method does accomplish our goal, it has several important drawbacks. The
biggest problem is that this method causes each page to be treated as a separate transaction. Besides making
it difficult to maintain your transactional integrity, Response.Redirect introduces some additional headaches.
First, it prevents good encapsulation of code. Second, you lose access to all of the properties in the Request
object. Sure, there are workarounds, but they're difficult. Finally, Response.Redirect necessitates a round trip
to       the     client,     which,      on     high-volume       sites,     causes    scalability    problems.
As you might suspect, Server.Transfer fixes all of these problems. It does this by performing the transfer on
the server without requiring a roundtrip to the client.

70. How can you provide an alternating color scheme in a Repeater control? AlternatingItemTemplate
Like the ItemTemplate element, but rendered for every other row (alternating items) in the Repeater control.
You can specify a different appearance for the AlternatingItemTemplate element by setting its style properties.

71. Which template must you provide, in order to display data in a Repeater control?
ItemTemplate

72. What event handlers can I include in Global.asax?
Application_Start,Application_End, Application_AcquireRequestState, Application_AuthenticateRequest,
Application_AuthorizeRequest, Application_BeginRequest, Application_Disposed, Application_EndRequest,
Application_Error, Application_PostRequestHandlerExecute, Application_PreRequestHandlerExecute,
Application_PreSendRequestContent, Application_PreSendRequestHeaders, Application_ReleaseRequestState,
Application_ResolveRequestCache, Application_UpdateRequestCache, Session_Start,Session_End
You can optionally include "On" in any of method names. For example, you can name a BeginRequest event
handler.Application_BeginRequest or Application_OnBeginRequest.You can also include event handlers in
Global.asax for events fired by custom HTTP modules.Note that not all of the event handlers make sense for
Web Services (they're designed for ASP.NET applications in general, whereas .NET XML Web Services are
specialized instances of an ASP.NET app). For example, the Application_AuthenticateRequest and
Application_AuthorizeRequest events are designed to be used with ASP.NET Forms authentication.

73.        What         is        different       b/w         webconfig.xml           &       Machineconfig.xml
Web.config & machine.config both are configuration files.Web.config contains settings specific to an application
where as machine.config contains settings to a computer. The Configuration system first searches settings in
machine.config file & then looks in application configuration files.Web.config, can appear in multiple
directories on an ASP.NET Web application server. Each Web.config file applies configuration settings to its own
directory and all child directories below it. There is only Machine.config file on a web server.
If I'm developing an application that must accomodate multiple security levels though secure login and my
ASP.NET web appplication is spanned across three web-servers (using round-robbin load balancing) what
would     be     the      best    approach       to    maintain     login-in    state    for    the      users?
Use the state server or store the state in the database. This can be easily done through simple setting change
in                                                the                                              web.config.
<SESSIONSTATE
StateConnectionString="tcpip=127.0.0.1:42424"
sqlConnectionString="data             source=127.0.0.1;            user           id=sa;           password="
cookieless="false"
timeout="30"
/>

You can specify mode as ―stateserver‖ or ―sqlserver‖.

Where would you use an iHTTPModule, and what are the limitations of any approach you might take in
implementing                                                                                            one
"One of ASP.NET's most useful features is the extensibility of the HTTP pipeline, the path that data takes
between client and server. You can use them to extend your ASP.NET applications by adding pre- and post-
processing to each HTTP request coming into your application. For example, if you wanted custom
authentication facilities for your application, the best technique would be to intercept the request when it
comes in and process the request in a custom HTTP module.

74. How do you turn off cookies for one page in your site?
Since no Page Level directive is present, I am afraid that cant be done.

75.           How          do           you           create          a         permanent            cookie?
Permanent cookies are available until a specified expiration date, and are stored on the hard disk.So Set the
'Expires' property any value greater than DataTime.MinValue with respect to the current datetime. If u want
the cookie which never expires set its Expires property equal to DateTime.maxValue.

76. Which method do you use to redirect the user to another page without performing a round trip
to the client?
Server.Transfer and Server.Execute

77. What property do you have to set to tell the grid which page to go to when using the Pager
object?
CurrentPageIndex

78. Should validation (did the user enter a real date) occur server-side or client-side? Why? It
should occur both at client-side and Server side.By using expression validator control with the specified
expression ie.. the regular expression provides the facility of only validatating the date specified is in the
correct format or not. But for checking the date where it is the real data or not should be done at the server
side, by getting the system date ranges and checking the date whether it is in between that range or not.

79. What does the "EnableViewState" property do? Why would I want it on or off? Enable ViewState
turns on the automatic state management feature that enables server controls to re-populate their values on a
round trip without requiring you to write any code. This feature is not free however, since the state of a control
is passed to and from the server in a hidden form field. You should be aware of when ViewState is helping you
and when it is not. For example, if you are binding a control to data on every round trip, then you do not need
the control to maintain it's view state, since you will wipe out any re-populated data in any case. ViewState is
enabled for all server controls by default. To disable it, set the EnableViewState property of the control to
false.

80. What is the difference between Server.Transfer and Response.Redirect? Why would I choose
one over the other? Server.Transfer() : client is shown as it is on the requesting page only, but the all the
content is of the requested page. Data can be persist accros the pages using Context.Item collection, which is
one of the best way to transfer data from one page to another keeping the page state alive.

Response.Dedirect() :client know the physical location (page name and query string as well). Context.Items
loses the persisitance when nevigate to destination page. In earlier versions of IIS, if we wanted to send a
user to a new Web page, the only option we had was Response.Redirect. While this method does accomplish
our goal, it has several important drawbacks. The biggest problem is that this method causes each page to be
treated as a separate transaction. Besides making it difficult to maintain your transactional integrity,
Response.Redirect introduces some additional headaches. First, it prevents good encapsulation of code.
Second, you lose access to all of the properties in the Request object. Sure, there are workarounds, but
they're difficult. Finally, Response.Redirect necessitates a round trip to the client, which, on high-volume sites,
causes scalability problems. As you might suspect, Server.Transfer fixes all of these problems. It does this by
performing the transfer on the server without requiring a roundtrip to the client.

81. Can you give an example of when it would be appropriate to use a web service as opposed to a
non-serviced .NET component?


        Communicating through a Firewall When building a distributed application with 100s/1000s of users
         spread over multiple locations, there is always the problem of communicating between client and
         server because of firewalls and proxy servers. Exposing your middle tier components as Web Services
         and invoking the directly from a Windows UI is a very valid option.
        Application Integration When integrating applications written in various languages and running on
         disparate systems. Or even applications running on the same platform that have been written by
         separate vendors.
        Business-to-Business Integration This is an enabler for B2B intergtation which allows one to expose
         vital business processes to authorized supplier and customers. An example would be exposing
         electronic ordering and invoicing, allowing customers to send you purchase orders and suppliers to
         send you invoices electronically.
        Software Reuse This takes place at multiple levels. Code Reuse at the Source code level or binary
         componet-based resuse. The limiting factor here is that you can reuse the code but not the data
         behind it. Webservice overcome this limitation. A scenario could be when you are building an app that
         aggregates the functionality of serveral other Applicatons. Each of these functions could be performed
         by individual apps, but there is value in perhaps combining the the multiple apps to present a unifiend
         view in a Portal or Intranet.
        When not to use Web Services: Single machine Applicatons When the apps are running on the same
         machine and need to communicate with each other use a native API. You also have the options of
         using component technologies such as COM or .NET Componets as there is very little overhead.
        Homogeneous Applications on a LAN If you have Win32 or Winforms apps that want to communicate
         to their server counterpart. It is much more efficient to use DCOM in the case of Win32 apps and .NET
         Remoting in the case of .NET Apps

82. Can you give an example of what might be best suited to place in the Application_Start and
Session_Start                                                                                  subroutines?
The Application_Start event is guaranteed to occur only once throughout the lifetime of the application. It's a
good place to initialize global variables. For example, you might want to retrieve a list of products from a
database table and place the list in application state or the Cache object. SessionStateModule exposes both
Session_Start and Session_End events.

83. What are the advantages and disadvantages of viewstate?
The primary advantages of the ViewState feature in ASP.NET are:

1. Simplicity. There is no need to write possibly complex code to store form data between page submissions.
2. Flexibility. It is possible to enable, configure, and disable ViewState on a control-by-control basis, choosing
to persist the values of some fields but not others.

There are, however a few disadvantages that are worth pointing out:

1. Does not track across pages. ViewState information does not automatically transfer from page to page. With
the session
approach, values can be stored in the session and accessed from other pages. This is not possible with
ViewState, so storing
data into the session must be done explicitly.

2. ViewState is not suitable for transferring data for back-end systems. That is, data still has to be transferred
to the back
end using some form of data object.
84. Describe session handling in a webfarm, how does it work and what are the limits? ASP.NET
Session supports storing of session data in 3 ways, i] in In-Process ( in the same memory that ASP.NET uses) ,
ii] out-of-process using Windows NT Service )in separate memory from ASP.NET ) or iii] in SQL Server
(persistent storage). Both the Windows Service and SQL Server solution support a webfarm scenario where all
the     web-servers      can     be    configured       to     share     common      session    state   store.

1. Windows Service : We can start this service by Start | Control Panel | Administrative Tools | Services | . In
that we service names ASP.NET State Service. We can start or stop service by manually or configure to start
automatically. Then we have to configure our web.config file



<CONFIGURATION><configuration>
 <system.web>
  <SessionState
   mode = ―StateServer‖
   stateConnectionString = ―tcpip=127.0.0.1:42424‖
   stateNetworkTimeout = ―10‖
   sqlConnectionString=‖data source = 127.0.0.1; uid=sa;pwd=‖
   cookieless =‖Flase‖
   timeout= ―20‖ />
 </system.web>
</configuration> </SYSTEM.WEB>
</CONFIGURATION>
Here ASP.Net Session is directed to use Windows Service for state management on local server (address :
127.0.0.1 is TCP/IP loop-back address). The default port is 42424. we can configure to any port but for that
we have to manually edit the registry.
 Follow these simple steps
- In a webfarm make sure you have the same config file in all your web servers.
- Also make sure your objects are serializable.
- For session state to be maintained across different web servers in the webfarm, the application path of the
web-site in the IIS Metabase should be identical in all the web-servers in the webfarm.

85. Which template must you provide, in order to display data in a Repeater control?
You have to use the ItemTemplate to Display data. Syntax is as follows,
 < ItemTemplate >
  < div class =‖rItem‖ >
     < img src=‖images/<%# Container.DataItem(―ImageURL‖)%>‖ hspace=‖10‖ />
  < b > <% # Container.DataItem(―Title‖)%>
  < /div >
 < ItemTemplate >

How can you provide an alternating color scheme in a Repeater control?
Using the AlternatintItemTemplate

86. What property must you set, and what method must you call in your code, in order to bind the
data from some data source to the Repeater control? Set the DataMember property to the name of the
table to bind to. (If this property is not set, by default the first table in the dataset is used.) DataBind method,
use this method to bind data from a source to a server control. This method is commonly used after retrieving
a data set through a database query.

87.    What     method        do     you     use       to   explicitly   kill   a          user     s     session?
You can dump (Kill) the session yourself by calling the method Session.Abandon.

ASP.NET automatically deletes a user's Session object, dumping its contents, after it has been idle for a
configurable timeout interval. This interval, in minutes, is set in the <SESSIONSTATE>section of the
web.config file. The default is 20 minutes.

88.      How       do     you      turn     off     cookies      for    one      page      in    your      site?
Use Cookie.Discard property, Gets or sets the discard flag set by the server. When true, this property instructs
the client application not to save the Cookie on the user's hard disk when a session ends.

89. Which two properties are on every validation control?
We have two common properties for every validation controls
1. Control to Validate,
2. Error Message.

90. What tags do you need to add within the asp:datagrid tags to bind columns manually?

< asp:DataGrid id="dgCart" AutoGenerateColumns="False" CellPadding="4" Width="448px" runat="server" >
< Columns >
< asp:ButtonColumn HeaderText="SELECT" Text="SELECT" CommandName="select" >< /asp:ButtonColumn
>
< asp:BoundColumn DataField="ProductId" HeaderText="Product ID" > < /asp:BoundColumn >
< asp:BoundColumn DataField="ProductName" HeaderText="Product Name" >< /asp:BoundColumn >
< asp:BoundColumn DataField="UnitPrice" HeaderText="UnitPrice" >   </asp:BoundColumn >
< /Columns >
< /asp:DataGrid >

91. How do you create a permanent cookie? Permanent cookies are the ones that are most useful.
Permanent cookies are available until a specified expiration date, and are stored on the hard disk. The location
of cookies differs with each browser, but this doesn‘t matter, as this is all handled by your browser and the
server. If you want to create a permanent cookie called Name with a value of Nigel, which expires in one
month, you‘d use the following code Response.Cookies ("Name") = "Nigel" Response.Cookies ("Name").
Expires = DateAdd ("m", 1, Now ())

92. What tag do you use to add a hyperlink column to the DataGrid?
< asp:HyperLinkColumn > </ asp:HyperLinkColumn>

93. Which method do you use to redirect the user to another page without performing a round trip
to the client?
Server.transfer

94. What is the transport protocol you use to call a Web service SOAP ?
HTTP Protocol

95. Explain role based security ? Role Based Security lets you identify groups of users to allow or deny
based on their role in the organization.In Windows NT and Windows XP, roles map to names used to identify
user groups. Windows defines several built-in groups, including Administrators, Users, and Guests.To allow or
deny access to certain groups of users, add the <ROLES>element to the authorization list in your Web
application's Web.config file.e.g.

<AUTHORIZATION>< authorization >
  < allow roles="Domain Name\Administrators" / > < !-- Allow Administrators in domain. -- >
  < deny users="*" / >                  < !-- Deny anyone else. -- >
< /authorization >

96. How do you register JavaScript for webcontrols ?
You can register javascript for controls using <CONTROL -name>Attribtues.Add(scriptname,scripttext)
method.

97.       When        do       you       set        "<IDENTITY          impersonate="true"      />"        ?
Identity is a webconfig declaration under System.web, which helps to control the application Identity of the
web applicaton. Which can be at any level(Machine,Site,application,subdirectory,or page), attribute
impersonate with "true" as value specifies that client impersonation is used.

98. What are different templates available in Repeater,DataList and Datagrid ? Templates enable one
to apply complicated formatting to each of the items displayed by a control.Repeater control supports five
types of templates.HeaderTemplate controls           how the header of the repeater control is
formatted.ItemTemplate controls the formatting of each item displayed.AlternatingItemTemplate controls how
alternate items are formatted and the SeparatorTemplate displays a separator between each item
displyed.FooterTemplate is used for controlling how the footer of the repeater control is formatted.The
DataList and Datagrid supports two templates in addition to the above five.SelectedItem Template controls
how a selected item is formatted and EditItemTemplate controls how an item selected for editing is formatted.
99.         What        is      ViewState       ?      and       how        it       is      managed         ?
ASP.NET ViewState is a new kind of state service that developers can use to track UI state on a per-user
basis. Internally it uses an an old Web programming trick-roundtripping state in a hidden form field and bakes
it right into the page-processing framework.It needs less code to write and maintain state in your Web-based
forms.

100. What is web.config file ? Web.config file is the configuration file for the Asp.net web application.
There is one web.config file for one asp.net application which configures the particular application. Web.config
file is written in XML with specific tags having specific meanings.It includes databa which includes
connections,Session States,Error Handling,Security etc. For example :

< configuration >
< appSettings >
   < add key="ConnectionString"
      value="server=localhost;uid=sa;pwd=;database=MyDB" / >
< /appSettings >
< /configuration >



101.        What       is     advantage        of      viewstate       and       what      are      benefits?
When a form is submitted in classic ASP, all form values are cleared. Suppose you have submitted a form with
a lot of information and the server comes back with an error. You will have to go back to the form and correct
the information. You click the back button, and what happens.......ALL form values are CLEARED, and you will
have to start all over again! The site did not maintain your ViewState.With ASP .NET, the form reappears in
the browser window together with all form values.This is because ASP .NET maintains your ViewState. The
ViewState indicates the status of the page when submitted to the server.

102. What tags do you need to add within the asp:datagrid tags to bind columns manually? Set
AutoGenerateColumns Property to false on the datagrid tag and then use Column tag and an ASP:databound
tag

< asp:DataGrid runat="server" id="ManualColumnBinding" AutoGenerateColumns="False" >
 < Columns >
   < asp:BoundColumn HeaderText="Column1" DataField="Column1"/ >
   < asp:BoundColumn HeaderText="Column2" DataField="Column2"/ >
 < /Columns >
< /asp:DataGrid >
<asp:DataGrid id=ManualColumnBinding runat="server" AutoGenerateColumns="False">
<COLUMNS> <asp:BoundColumn HeaderText="Column2" DataField="Column2"></asp:BoundColumn>
</asp:DataGrid>

103. Which property on a Combo Box do you set with a column name, prior to setting the
DataSource, to display data in the combo box? DataTextField and DataValueField

104. Which control would you use if you needed to make sure the values in two different controls
matched? CompareValidator is used to ensure that two fields are identical.

105.        What      is     validationsummary          server       control?where        it      is     used?.
The ValidationSummary control allows you to summarize the error messages from all validation controls on a
Web page in a single location. The summary can be displayed as a list, a bulleted list, or a single paragraph,
based on the value of the DisplayMode property. The error message displayed in the ValidationSummary
control for each validation control on the page is specified by the ErrorMessage property of each validation
control. If the ErrorMessage property of the validation control is not set, no error message is displayed in the
ValidationSummary control for that validation control. You can also specify a custom title in the heading
section of the ValidationSummary control by setting the HeaderText property. You can control whether the
ValidationSummary control is displayed or hidden by setting the ShowSummary property. The summary can
also be displayed in a message box by setting the ShowMessageBox property to true.
106. What is the sequence of operation takes place when a page is loaded?
BeginTranaction - only if the request is transacted
Init - every time a page is processed
LoadViewState - Only on postback
ProcessPostData1 - Only on postback
Load - every time
ProcessData2 - Only on Postback
RaiseChangedEvent - Only on Postback
RaisePostBackEvent - Only on Postback
PreRender - everytime
BuildTraceTree - only if tracing is enabled
SaveViewState - every time
Render - Everytime
End Transaction - only if the request is transacted
Trace.EndRequest - only when tracing is enabled
UnloadRecursive - Every request

107. Difference between asp and asp.net?.
"ASP (Active Server Pages) and ASP.NET are both server side technologies for building web sites and web
applications, ASP.NET is Managed compiled code - asp is interpreted. and ASP.net is fully Object oriented.
ASP.NET has been entirely re-architected to provide a highly productive programming experience based on the
.NET Framework, and a robust infrastructure for building reliable and scalable web
applications."

108. Name the validation control available in asp.net?.
RequiredField, RangeValidator,RegularExpression,Custom validator,compare Validator

109. What are the various ways of securing a web site that could prevent from hacking etc .. ?
1) Authentication/Authorization
2) Encryption/Decryption
3) Maintaining web servers outside the corporate firewall. etc.,

110.       What        is      the        difference        between          in-proc       and       out-of-proc?
An inproc is one which runs in the same process area as that of the client giving tha advantage of speed but
the disadvantage of stability becoz if it crashes it takes the client application also with it.Outproc is one which
works outside the clients memory thus giving stability to the client, but we have to compromise a bit on speed.

111. When you’re running a component within ASP.NET, what process is it running within on
Windows XP? Windows 2000? Windows 2003? On Windows 2003 (IIS 6.0) running in native mode, the
component is running within the w3wp.exe process associated with the application pool which has been
configured for the web application containing the component.

On Windows 2003 in IIS 5.0 emulation mode, 2000, or XP, it's running within the IIS helper process whose
name I do not remember, it being quite a while since I last used IIS 5.0.

112. What does aspnet_regiis -i do ? Aspnet_regiis.exe is The ASP.NET IIS Registration tool allows an
administrator or installation program to easily update the script maps for an ASP.NET application to point to
the ASP.NET ISAPI version associated with the tool. The tool can also be used to display the status of all
installed versions of ASP. NET, register the ASP.NET version coupled with the tool, create client-script
directories,            and           perform            other            configuration          operations.
When multiple versions of the .NET Framework are executing side-by-side on a single computer, the ASP.NET
ISAPI version mapped to an ASP.NET application determines which version of the common language runtime is
used for the application.

The tool can be launched with a set of optional parameters. Option "i" Installs the version of ASP.NET
associated with Aspnet_regiis.exe and updates the script maps at the IIS metabase root and below. Note that
only applications that are currently mapped to an earlier version of ASP.NET are affected

113. What is a PostBack?
The process in which a Web page sends data back to the same page on the server.
114. What is ViewState? How is it encoded? Is it encrypted? Who uses ViewState? ViewState is the
mechanism ASP.NET uses to keep track of server control state values that don't otherwise post back as part of
the      HTTP       form.      ViewState       Maintains    the       UI      State      of      a      Page
    ViewState is base64-encoded.       It is not encrypted but it can be encrypted by setting
EnableViewStatMAC="true" & setting the machineKey validation type to 3DES. If you want to NOT maintain
the ViewState, include the directive < %@ Page EnableViewState="false" % > at the top of an .aspx page or
add the attribute EnableViewState="false" to any control.

115. What is the < machinekey > element and what two ASP.NET technologies is it used for?
Configures keys to use for encryption and decryption of forms authentication cookie data and view state data,
and for verification of out-of-process session state identification.There fore 2 ASP.Net technique in which it is
used are Encryption/Decryption & Verification

116. What three Session State providers are available in ASP.NET 1.1? What are the pros and cons
of each? ASP.NET provides three distinct ways to store session data for your application: in-process session
state, out-of-process session state as a Windows service, and out-of-process session state in a SQL Server
database. Each has it advantages.

1.In-process session-state mode
Limitations:
 * When using the in-process session-state mode, session-state data is lost if aspnet_wp.exe or the application
domain restarts.
 * If you enable Web garden mode in the < processModel > element of the application's Web.config file, do not
use in-process session-state mode. Otherwise, random data loss can occur.
Advantage:
 * in-process session state is by far the fastest solution. If you are storing only small amounts of volatile data
in session state, it is recommended that you use the in-process provider.

2. The State Server simply stores session state in memory when in out-of-proc mode. In this mode the worker
process talks directly to the State Server

3. SQL mode, session states are stored in a SQL Server database and the worker process talks directly to SQL.
The ASP.NET worker processes are then able to take advantage of this simple storage service by serializing
and saving (using .NET serialization services) all objects within a client's Session collection at the end of each
Web request
 Both these out-of-process solutions are useful primarily if you scale your application across multiple
processors or multiple computers, or where data cannot be lost if a server or process is restarted.

117.       What      is     the     difference       between         HTTP-Post        and      HTTP-Get?
As their names imply, both HTTP GET and HTTP POST use HTTP as their underlying protocol. Both of these
methods     encode    request   parameters     as    name/value      pairs    in   the    HTTP   request.
The GET method creates a query string and appends it to the script's URL on the server that handles the
request.
The POST method creates a name/value pairs that are passed in the body of the HTTP request message.

118. Name and describe some HTTP Status Codes and what they express to the requesting client.
When users try to access content on a server that is running Internet Information Services (IIS) through HTTP
or File Transfer Protocol (FTP), IIS returns a numeric code that indicates the status of the request. This status
code is recorded in the IIS log, and it may also be displayed in the Web browser or FTP client. The status code
can indicate whether a particular request is successful or unsuccessful and can also reveal the exact reason
why a request is unsuccessful. There are 5 groups ranging from 1xx - 5xx of http status codes exists.

101 - Switching protocols.

200 - OK. The client request has succeeded

302 - Object moved.

400 - Bad request.

50013 - Web server is too busy.
119. Explain < @OutputCache% > and the usage of VaryByParam, VaryByHeader. OutputCache is
used to control the caching policies of an ASP.NET page or user control. To cache a page @OutputCache
directive should be defined as follows < %@ OutputCache Duration="100" VaryByParam="none" %>

VaryByParam: A semicolon-separated list of strings used to vary the output cache. By default, these strings
correspond to a query string value sent with GET method attributes, or a parameter sent using the POST
method. When this attribute is set to multiple parameters, the output cache contains a different version of the
requested document for each specified parameter. Possible values include none, *, and any valid query string
or POST parameter name.

VaryByHeader: A semicolon-separated list of HTTP headers used to vary the output cache. When this attribute
is set to multiple headers, the output cache contains a different version of the requested document for each
specified header.




120. What is the difference between repeater over datalist and datagrid?The Repeater class is not
derived from the WebControl class, like the DataGrid and DataList. Therefore, the Repeater lacks the stylistic
properties common to both the DataGrid and DataList. What this boils down to is that if you want to format the
data displayed in the Repeater, you must do so in the HTML markup. The Repeater control provides the
maximum amount of flexibility over the HTML produced. Whereas the DataGrid wraps the DataSource contents
in an HTML < table >, and the DataList wraps the contents in either an HTML < table > or < span > tags
(depending on the DataList's RepeatLayout property), the Repeater adds absolutely no HTML content other
than what you explicitly specify in the templates. While using Repeater control, If we wanted to display the
employee names in a bold font we'd have to alter the "ItemTemplate" to include an HTML bold tag, Whereas
with the DataGrid or DataList, we could have made the text appear in a bold font by setting the control's
ItemStyle-Font-Bold property to True. The Repeater's lack of stylistic properties can drastically add to the
development time metric. For example, imagine that you decide to use the Repeater to display data that needs
to be bold, centered, and displayed in a particular font-face with a particular background color. While all this
can be specified using a few HTML tags, these tags will quickly clutter the Repeater's templates. Such clutter
makes it much harder to change the look at a later date. Along with its increased development time, the
Repeater also lacks any built-in functionality to assist in supporting paging, editing, or editing of data. Due to
this lack of feature-support, the Repeater scores poorly on the usability scale.

However, The Repeater's performance is slightly better than that of the DataList's, and is more noticeably
better than that of the DataGrid's. Following figure shows the number of requests per second the Repeater
could handle versus the DataGrid and DataList

121. Can we handle the error and redirect to some pages using web.config?

Yes, we can do this, but to handle errors, we must know the error codes; only then we can take the user to a
proper error message page, else it may confuse the user.
CustomErrors Configuration section in web.config file:
The default configuration is:
< customErrors mode="RemoteOnly" defaultRedirect="Customerror.aspx" >
  < error statusCode="404" redirect="Notfound.aspx" / >
< /customErrors >
If mode is set to Off, custom error messages will be disabled. Users will receive detailed exception error
messages.
If mode is set to On, custom error messages will be enabled.
If mode is set to RemoteOnly, then users will receive custom errors, but users accessing the site locally will
receive detailed error messages.
Add an < error > tag for each error you want to handle. The error tag will redirect the user to the
Notfound.aspx page when the site returns the 404 (Page not found) error.



[Example]

There is a page MainForm.aspx

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
      'Put user code to initialize the page here
Dim str As System.Text.StringBuilder
str.Append("hi") ' Error Line as str is not instantiated
Response.Write(str.ToString)
End Sub

[Web.Config]

< customErrors mode="On" defaultRedirect="Error.aspx"/ >
' a simple redirect will take the user to Error.aspx [user defined] error file.

< customErrors mode="RemoteOnly" defaultRedirect="Customerror.aspx" >
  < error statusCode="404" redirect="Notfound.aspx" / >
< /customErrors >
'This will take the user to NotFound.aspx defined in IIS.




122. How do you implement Paging in .Net?

The DataGrid provides the means to display a group of records from the data source (for example, the first
10), and then navigate to the "page" containing the next 10 records, and so on through the data.

Using Ado.Net we can explicit control over the number of records returned from the data source, as well as
how much data is to be cached locally in the DataSet.

1.Using DataAdapter.fill method give the value of 'Maxrecords' parameter (Note: - Don't use it because query
will return all records but fill the dataset based on value of 'maxrecords' parameter).



2.For SQL server database, combines a WHERE clause and a ORDER BY clause with TOP predicate.

3.If Data does not change often just cache records locally in DataSet and just take some records from the
DataSet to display.

123. What is the difference between Server.Transfer and Response.Redirect? Server.Transfer() :
client is shown as it is on the requesting page only, but the all the content is of the requested page. Data can
be persist across the pages using Context.Item collection, which is one of the best way to transfer data from
one page to another keeping the page state alive.

Response.Dedirect() :client knows the physical location (page name and query string as well). Context.Items
loses the persistence when navigate to destination page. In earlier versions of IIS, if we wanted to send a user
to a new Web page, the only option we had was Response.Redirect. While this method does accomplish our
goal, it has several important drawbacks. The biggest problem is that this method causes each page to be
treated as a separate transaction. Besides making it difficult to maintain your transactional integrity,
Response.Redirect introduces some additional headaches. First, it prevents good encapsulation of code.
Second, you lose access to all of the properties in the Request object. Sure, there are workarounds, but
they're difficult. Finally, Response.Redirect necessitates a round trip to the client, which, on high-volume sites,
causes scalability problems. As you might suspect, Server.Transfer fixes all of these problems. It does this by
performing      the    transfer   on   the     server   without   requiring     a    roundtrip    to   the  client.
Response.Redirect sends a response to the client browser instructing it to request the second page. This
requires a round-trip to the client, and the client initiates the Request for the second page. Server.Transfer
transfers the process to the second page without making a round-trip to the client. It also transfers the
HttpContext to the second page, enabling the second page access to all the values in the HttpContext of the
first page.

124. Can you create an app domain?

Yes, We can create user app domain by calling on of the following overload static methods of the
System.AppDomain class
1. Public static AppDomain CreateDomain(String friendlyName)
2. Public static AppDomain CreateDomain(String friendlyName, Evidence securityInfo)
3. Public static AppDomain CreateDomain(String friendlyName, Evidence securityInfo, AppDomainSetup info)
4. Public static AppDomain CreateDomain(String friendlyName, Evidence securityInfo, String appBasePath,
String appRelativeSearchPath, bool shadowCopyFiles)



125. What are the various security methods which IIS Provides apart from .NET ?

The various security methods which IIS provides are

a) Authentication Modes
b) IP Address and Domain Name Restriction
c) DNS Lookups DNS Lookups
d) The Network ID and Subnet Mask
e) SSL



126. What is Web Gardening? How would using it affect a design?

The Web Garden Model: The Web garden model is configurable through the section of the machine.config file.
Notice that the section is the only configuration section that cannot be placed in an application-specific
web.config file. This means that the Web garden mode applies to all applications running on the machine.
However, by using the node in the machine.config source, you can adapt machine-wide settings on a per-
application basis.

Two attributes in the section affect the Web garden model. They are webGarden and cpuMask. The webGarden
attribute takes a Boolean value that indicates whether or not multiple worker processes (one per each
affinitized CPU) have to be used. The attribute is set to false by default. The cpuMask attribute stores a
DWORD value whose binary representation provides a bit mask for the CPUs that are eligible to run the
ASP.NET worker process. The default value is -1 (0xFFFFFF), which means that all available CPUs can be used.
The contents of the cpuMask attribute is ignored when the webGarden attribute is false. The cpuMask attribute
also sets an upper bound to the number of copies of aspnet_wp.exe that are running.

Web gardening enables multiple worker processes to run at the same time. However, you should note that all
processes will have their own copy of application state, in-process session state, ASP.NET cache, static data,
and all that is needed to run applications. When the Web garden mode is enabled, the ASP.NET ISAPI launches
as many worker processes as there are CPUs, each a full clone of the next (and each affinitized with the
corresponding CPU). To balance the workload, incoming requests are partitioned among running processes in a
round-robin manner. Worker processes get recycled as in the single processor case. Note that ASP.NET inherits
any CPU usage restriction from the operating system and doesn't include any custom semantics for doing this.

All in all, the Web garden model is not necessarily a big win for all applications. The more stateful applications
are, the more they risk to pay in terms of real performance. Working data is stored in blocks of shared
memory so that any changes entered by a process are immediately visible to others. However, for the time it
takes to service a request, working data is copied in the context of the process. Each worker process,
therefore, will handle its own copy of working data, and the more stateful the application, the higher the cost
in performance. In this context, careful and savvy application benchmarking is an absolute must.

Changes made to the section of the configuration file are effective only after IIS is restarted. In IIS 6, Web
gardening parameters are stored in the IIS metabase; the webGarden and cpuMask attributes are ignored.

127.       What        is     view      state?.where          it    stored?.can       we       disable      it?
The web is state-less protocol, so the page gets instantiated, executed, rendered and then disposed on every
round trip to the server. The developers code to add "statefulness" to the page by using Server-side storage
for the state or posting the page to itself. When require to persist and read the data in control on webform,
developer had to read the values and store them in hidden variable (in the form), which were then used to
restore the values. With advent of .NET framework, ASP.NET came up with ViewState mechanism, which
tracks the data values of server controls on ASP.NET webform. In effect,ViewState can be viewed as "hidden
variable managed by ASP.NET framework!". When ASP.NET page is executed, data values from all server
controls on page are collected and encoded as single string, which then assigned to page's hidden atrribute "<
input type=hidden >", that is part of page sent to the client.
ViewState value is temporarily saved in the client's browser.ViewState can be disabled for a single control, for
an entire page orfor an entire web application. The syntax is:

Disable ViewState for control (Datagrid in this example)
< asp:datagrid EnableViewState="false" ... / >

Disable ViewState for a page, using Page directive
< %@ Page EnableViewState="False" ... % >

Disable ViewState for application through entry in web.config
< Pages EnableViewState="false" ... / >




                                       Web Service Questions

01. What is the transport protocol you use to call a Web service?
Ans : SOAP (Simple Object Access Protocol) is the preferred protocol.

02.     True     or     False:     A     Web       service      can     only       be   written      in     .NET?
Ans : False

03. What does WSDL stand for?
Ans : Web Services Description Language.

04. Where on the Internet would you look for Web services?
Ans : http://www.uddi.org/

05. True or False: To test a Web service you must create a Windows application or Web application
to consume this service?
Ans : False, the web service comes with a test page and it provides HTTP-GET method to test.

06. Can you give an example of when it would be appropriate to use a web service as opposed to
non-serviced                                            .NET                                         component
Web service is one of main component in Service Oriented Architecture. You could use web services when your
clients and servers are running on different networks and also different platforms. This provides a loosely
coupled system. And also if the client is behind the firewall it would be easy to use web service since it runs on
port 80 (by default) instead of having some thing else in Service Oriented Architecture applications. What is
the      standard      you     use        to     wrap      up       a      call    to     a      Web        service
"SOAP."

07.   What    is      the   transport     protocol     you    use     to    call    a   Web     service    SOAP.
HTTP with SOAP

08. What does WSDL stand for? "WSDL stands for Web Services Dsescription Langauge. There is
WSDL.exe that creates a .wsdl Files which defines how an XML Web service behaves and instructs clients as to
how                 to                interact              with               the                  service.
eg: wsdl http://LocalHost/WebServiceName.asmx"

09. Where on the Internet would you look for Web Services?
http://www.uddi.org/

10. What does WSDL stand for?
Web Services Description Language

11. True or False: To test a Web service you must create a windows application or Web application
to consume this service?
False.
12.          What     are     the    various     ways       of     accessing       a     web      service   ?
1.Asynchronous                                                                                            Call
  Application can make a call to the Webservice and then continue todo watever oit wants to do.When the
service is ready it will notify the application.Application can use BEGIN and END method to make
asynchronous call to the webmethod.We can use either a WaitHandle or a Delegate object when making
asynchronous call.
The WaitHandle class share resources between several objects. It provides several methods which will wait for
the resources to become available
The easiest and most powerful way to to implement an asynchronous call is using a delegate object. A
delegate object wraps up a callback function. The idea is to pass a method in the invocation of the web
method. When the webmethod has finished it will call this callback function to process the result

2.Synchronous Call
Application has to wait until execution has completed.




13. What are VSDISCO files?
 VSDISCO files are DISCO files that support dynamic discovery of Web services. If you place the following
VSDISCO file in a directory on your Web server, for example, it returns references to all ASMX and DISCO
files in the host directory and any subdirectories not noted in <EXCLUDE>elements:


           <DYNAMICDISCOVERY
            xmlns="urn:schemas-dynamicdiscovery:disco.2000-03-17">
            <EXCLUDE path="_vti_cnf" />
            <EXCLUDE path="_vti_pvt" />
            <EXCLUDE path="_vti_log" />
            <EXCLUDE path="_vti_script" />
            <EXCLUDE path="_vti_txt" />
           </DYNAMICDISCOVERY>

14. How does dynamic discovery work? ASP.NET maps the file name extension VSDISCO to an HTTP
handler that scans the host directory and subdirectories for ASMX and DISCO files and returns a dynamically
generated DISCO document. A client who requests a VSDISCO file gets back what appears to be a static
DISCO document.

Note that VSDISCO files are disabled in the release version of ASP.NET. You can reenable them by
uncommenting the line       in the <HTTPHANDLERS>section of Machine.config that maps *.vsdisco to
System.Web.Services.Discovery.DiscoveryRequestHandler and granting the ASPNET user account permission
to read the IIS metabase. However, Microsoft is actively discouraging the use of VSDISCO files because they
could represent a threat to Web server security.

15. Is it possible to prevent a browser from caching an ASPX page?
Just call SetNoStore on the HttpCachePolicy object exposed through the Response object's Cache property, as
demonstrated here:

     <%@ Page Language="C#" %>


        <%
         Response.Cache.SetNoStore ();
         Response.Write (DateTime.Now.ToLongTimeString ());
        %>



SetNoStore works by returning a Cache-Control: private, no-store header in the HTTP response. In this
example, it prevents caching of a Web page that shows the current time.

16. What does AspCompat="true" mean and when should I use it?
AspCompat is an aid in migrating ASP pages to ASPX pages. It defaults to false but should be set to true in any
ASPX  file   that   creates apartment-threaded      COM objects--that        is,   COM objects       registered
ThreadingModel=Apartment. That includes all COM objects written with Visual Basic 6.0. AspCompat should
also be set to true (regardless of threading model) if the page creates COM objects that access intrinsic ASP
objects such as Request and Response. The following directive sets AspCompat to true:
       <%@ Page AspCompat="true" %>
Setting AspCompat to true does two things. First, it makes intrinsic ASP objects available        to the COM
components by placing unmanaged wrappers around the equivalent ASP.NET objects. Second, it improves the
performance of calls that the page places to apartment- threaded COM objects by ensuring that the page
(actually, the thread that processes the request for the page) and the COM objects it creates share an
apartment. AspCompat="true" forces ASP.NET request threads into single-threaded apartments (STAs). If
those threads create COM objects marked ThreadingModel=Apartment, then the objects are created in the
same STAs as the threads that created them. Without AspCompat="true," request threads run in a
multithreaded apartment (MTA) and each call to an STA-based COM object incurs a performance hit when it's
marshaled across apartment boundaries.
Do not set AspCompat to true if your page uses no COM objects or if it uses COM objects that don't access ASP
intrinsic objects and that are registered ThreadingModel=Free or ThreadingModel=Both.




17. Can two different programming languages be mixed in a single ASMX file?
No.

18. What namespaces are imported by default in ASMX files?
The following namespaces are imported by default. Other namespaces must be imported manually.· System,
System.Collections,System.ComponentModel,System.Data,
System.Diagnostics,System.Web,System.Web.Services
How do I provide information to the Web Service when the information is required as a SOAP Header?
The key here is the Web Service proxy you created using wsdl.exe or through Visual Studio .NET's Add Web
Reference menu option. If you happen to download a WSDL file for a Web Service that requires a SOAP
header, .NET will create a SoapHeader class in the proxy source file. Using the previous example:
    public class Service1 : System.Web.Services.Protocols.SoapHttpClientProtocol
     {
         public AuthToken AuthTokenValue;

     [System.Xml.Serialization.XmlRootAttribute(Namespace="http://tempuri.org/", IsNullable=false)]
       public class AuthToken : SoapHeader {      public string Token; }}

In this case, when you create an instance of the proxy in your main application file, you'll also create an
instance of the AuthToken class and assign the string:
    Service1 objSvc = new Service1();
    processingobjSvc.AuthTokenValue = new AuthToken();
    objSvc.AuthTokenValue.Token = <ACTUAL token value>;
    Web Servicestring strResult = objSvc.MyBillableWebMethod();

19. What is WSDL?
WSDL is the Web Service Description Language, and it is implemented as a specific XML vocabulary. While it's
very much more complex than what can be described here, there are two important aspects to WSDL with
which you should be aware. First, WSDL provides instructions to consumers of Web Services to describe the
layout and contents of the SOAP packets the Web Service intends to issue. It's an interface description
document, of sorts. And second, it isn't intended that you read and interpret the WSDL. Rather, WSDL should
be processed by machine, typically to generate proxy source code (.NET) or create dynamic proxies on the fly
(the SOAP Toolkit or Web Service Behavior).

20. What is a Windows Service and how does its lifecycle differ from a "standard" EXE?
Windows service is a application that runs in the background. It is equivalent to a NT service.
The executable created is not a Windows application, and hence you can't just click and run it . it needs to be
installed as a service, VB.Net has a facility where we can add an installer to our program and then use a utility
to install the service. Where as this is not the case with standard exe

21. How can a win service developed in .NET be installed or used in Win98?Windows service cannot be
installed on Win9x machines even though the .NET framework runs on machine.

22. Can you debug a Windows Service? How ?
Yes we can debug a Windows Service.
Attach the WinDbg debugger to a service after the service starts
This method is similar to the method that you can use to attach a debugger to a process and then debug a
process.
Use the process ID of the process that hosts the service that you want to debug
1 To determine the process ID (PID) of the process that hosts the service that you want to debug, use one of
the following methods.
 • Method 1: Use the Task Manager
  a. Right-click the taskbar, and then click Task Manager. The Windows Task Manager dialog box appears.
  b. Click the Processes tab of the Windows Task Manager dialog box.
  c. Under Image Name, click the image name of the process that hosts the service that you want to debug.
Note the process ID of this process as specified by the value of the corresponding PID field.
 • Method 2: Use the Task List Utility (tlist.exe)
  a. Click Start, and then click Run. The Run dialog box appears.
  b. In the Open box, type cmd, and then click OK.
  c. At the command prompt, change the directory path to reflect the location of the tlist.exe file on your
computer.

  Note The tlist.exe file is typically located in the following directory: C:\Program Files\Debugging Tools for
Windows
 d. At the command prompt, type tlist to list the image names and the process IDs of all processes that are
currently running on your computer.

  Note Make a note of the process ID of the process that hosts the service that you want to debug.
2 At a command prompt, change the directory path to reflect the location of the windbg.exe file on your
computer.

 Note If a command prompt is not open, follow steps a and b of Method 1. The windbg.exe file is typically
located in the following directory: C:\Program Files\Debugging Tools for Windows.
3 At the command prompt, type windbg –p ProcessID to attach the WinDbg debugger to the process that hosts
the service that you want to debug.

 Note ProcessID is a placeholder for the process ID of the process that hosts the service that you want to
debug.

Use the image name of the process that hosts the service that you want to debug

You can use this method only if there is exactly one running instance of the process that hosts the service that
you want to run. To do this, follow these steps:
1 Click Start, and then click Run. The Run dialog box appears.
2 In the Open box, type cmd, and then click OK to open a command prompt.
3 At the command prompt, change the directory path to reflect the location of the windbg.exe file on your
computer.

 Note The windbg.exe file is typically located in the following directory: C:\Program Files\Debugging Tools for
Windows.
4 At the command prompt, type windbg –pn ImageName to attach the WinDbg debugger to the process that
hosts the service that you want to debug.

 NoteImageName is a placeholder for the image name of the process that hosts the service that you want to
debug. The "-pn" command-line option specifies that the ImageName command-line argument is the image
name of a process.
back to the top
Start the WinDbg debugger and attach to the process that hosts the service that you want to debug

1 Start Windows Explorer.
2 Locate the windbg.exe file on your computer.

 Note The windbg.exe file is typically located in the following directory: C:\Program Files\Debugging Tools for
Windows
3 Run the windbg.exe file to start the WinDbg debugger.
4 On the File menu, click Attach to a Process to display the Attach to Process dialog box.
5 Click to select the node that corresponds to the process that hosts the service that you want to debug, and
then click OK.
6 In the dialog box that appears, click Yes to save base workspace information. Notice that you can now debug
the disassembled code of your service.
Configure a service to start with the WinDbg debugger attached
You can use this method to debug services if you want to troubleshoot service-startup-related problems.
1 Configure the "Image File Execution" options. To do this, use one of the following methods:
• Method 1: Use the Global Flags Editor (gflags.exe)
 a. Start Windows Explorer.
 b. Locate the gflags.exe file on your computer.

   Note The gflags.exe file is typically located in the following directory: C:\Program Files\Debugging Tools for
Windows.
  c. Run the gflags.exe file to start the Global Flags Editor.
  d. In the Image File Name text box, type the image name of the process that hosts the service that you want
to debug. For example, if you want to debug a service that is hosted by a process that has MyService.exe as
the image name, type MyService.exe.
  e. Under Destination, click to select the Image File Options option.
  f. Under Image Debugger Options, click to select the Debugger check box.
  g. In the Debugger text box, type the full path of the debugger that you want to use. For example, if you
want to use the WinDbg debugger to debug a service, you can type a full path that is similar to the following:
C:\Program Files\Debugging Tools for Windows\windbg.exe
  h. Click Apply, and then click OK to quit the Global Flags Editor.
 • Method 2: Use Registry Editor
  a. Click Start, and then click Run. The Run dialog box appears.
  b. In the Open box, type regedit, and then click OK to start Registry Editor.
  c. Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to
reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using
Registry Editor incorrectly. Use Registry Editor at your own risk.

  In Registry Editor, locate, and then right-click the following registry subkey:
  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
 d. Point to New, and then click Key. In the left pane of Registry Editor, notice that New Key #1 (the name of
a new registry subkey) is selected for editing.
 e. Type ImageName to replace New Key #1, and then press ENTER.

   Note ImageName is a placeholder for the image name of the process that hosts the service that you want to
debug. For example, if you want to debug a service that is hosted by a process that has MyService.exe as the
image name, type MyService.exe.
 f. Right-click the registry subkey that you created in step e.
 g. Point to New, and then click String Value. In the right pane of Registry Editor, notice that New Value #1,
the name of a new registry entry, is selected for editing.
  h. Replace New Value #1 with Debugger, and then press ENTER.
  i. Right-click the Debugger registry entry that you created in step h, and then click Modify. The Edit String
dialog box appears.
  j. In the Value data text box, type DebuggerPath, and then click OK.

   Note DebuggerPath is a placeholder for the full path of the debugger that you want to use. For example, if
you want to use the WinDbg debugger to debug a service, you can type a full path that is similar to the
following: C:\Program Files\Debugging Tools for Windows\windbg.exe
2 For the debugger window to appear on your desktop, and to interact with the debugger, make your service
interactive. If you do not make your service interactive, the debugger will start but you cannot see it and you
cannot issue commands. To make your service interactive, use one of the following methods:
 • Method 1: Use the Services console
  a. Click Start, and then point to Programs.
  b. On the Programs menu, point to Administrative Tools, and then click Services. The Services console
appears.
  c. In the right pane of the Services console, right-click ServiceName, and then click Properties.

   Note ServiceName is a placeholder for the name of the service that you want to debug.
  d. On the Log On tab, click to select the Allow service to interact with desktop check box under Local System
account, and then click OK.
 • Method 2: Use Registry Editor
  a. In Registry Editor, locate, and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ServiceName
   Note Replace ServiceName with the name of the service that you want to debug. For example, if you want to
debug a service named MyService, locate and then click the following registry key:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MyService
  b. Under the Name field in the right pane of Registry Editor, right-click Type, and then click Modify. The Edit
DWORD Value dialog box appears.
  c. Change the text in the Value data text box to the result of the binary OR operation with the binary value of
the current text and the binary value, 0x00000100, as the two operands. The binary value, 0x00000100,
corresponds to the SERVICE_INTERACTIVE_PROCESS constant that is defined in the WinNT.h header file on
your computer. This constant specifies that a service is interactive in nature.
3 When a service starts, the service communicates to the Service Control Manager how long the service must
have to start (the time-out period for the service). If the Service Control Manager does not receive a "service
started" notice from the service within this time-out period, the Service Control Manager terminates the
process that hosts the service. This time-out period is typically less than 30 seconds. If you do not adjust this
time-out period, the Service Control Manager ends the process and the attached debugger while you are trying
to debug. To adjust this time-out period, follow these steps:
 a. In Registry Editor, locate, and then right-click the following registry subkey:
  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control
 b. Point to New, and then click DWORD Value. In the right pane of Registry Editor, notice that New Value #1
(the name of a new registry entry) is selected for editing.
 c. Type ServicesPipeTimeout to replace New Value #1, and then press ENTER.
 d. Right-click the ServicesPipeTimeout registry entry that you created in step c, and then click Modify. The
Edit DWORD Value dialog box appears.
 e. In the Value data text box, type TimeoutPeriod, and then click OK

  Note TimeoutPeriod is a placeholder for the value of the time-out period (in milliseconds) that you want to set
for the service. For example, if you want to set the time-out period to 24 hours (86400000 milliseconds), type
86400000.
 f. Restart the computer. You must restart the computer for Service Control Manager to apply this change.
4 Start your Windows service. To do this, follow these steps:
 a. Click Start, and then point to Programs.
 b. On the Programs menu, point to Administrative Tools, and then click Services. The Services console
appears.
 c. In the right pane of the Services console, right-click ServiceName, and then click Start.

 Note ServiceName is a placeholder for the name of the service that you want to debug.




                                      C# Interview Questions

01. Does C# support multiple-inheritance?
Ans : No.

02. Who is a protected class-level variable available to?
Ans : It is available to any sub-class (a class inheriting this class).

03. Are private class-level variables inherited?
Ans : Yes, but they are not accessible. Although they are not visible or accessible via the class interface, they
are inherited.

04. Describe the accessibility modifier “protected internal”.
Ans : It is available to classes that are within the same assembly and derived from the specified base class.

05. What’s the top .NET class that everything is derived from?
Ans : System.Object.

06. What does the term immutable mean?
Ans : The data value may not be changed. Note: The variable value may be changed, but the original
immutable data value was discarded and a new data value was created in memory.

07. What’s the difference between System.String and System.Text.StringBuilder classes?
Ans : System.String is immutable. System.StringBuilder was designed with the purpose of having a mutable
string where a variety of operations can be performed.

08. What’s the advantage of using System.Text.StringBuilder over System.String?
Ans : StringBuilder is more efficient in cases where there is a large amount of string manipulation. Strings are
immutable, so each time a string is changed, a new instance in memory is created.

09. Can you store multiple data types in System.Array?
Ans : No.
10. What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
Ans : The Clone() method returns a new array (a shallow copy) object containing all the elements in the
original array. The CopyTo() method copies the elements into another existing array. Both perform a shallow
copy. A shallow copy means the contents (each array element) contains references to the same object as the
elements in the original array. A deep copy (which neither of these methods performs) would create a new
instance of each element's object, resulting in a different, yet identacle object.

11. How can you sort the elements of the array in descending order?
Ans : By calling Sort() and then Reverse() methods.

12. What’s the .NET collection class that allows an element to be accessed using a unique key?
Ans : HashTable.

13. What class is underneath the SortedList class?
Ans : A sorted HashTable.

14.    Will   the    finally    block    get     executed     if   an     exception     has     not    occurred?
Ans : Yes.

15. What’s the C# syntax to catch any possible exception?
Ans : A catch block that catches the exception of type System.Exception. You can also omit the parameter
data type in this case and just write catch {}.

16. Can multiple catch blocks be executed for a single try statement?
Ans : No. Once the proper catch block processed, control is transferred to the finally block (if there are any).

17. Explain the three services model commonly know as a three-tier application.
Ans : Presentation (UI), Business (logic and underlying code) and Data (from storage or other sources).




                                           Class Questions:


01. What is the syntax to inherit from a class in C#?
Ans : Place a colon and then the name of the base class.
Example: class MyNewClass : MyBaseClass

02. Can you prevent your class from being inherited by another class?
Ans : Yes. The keyword ―sealed‖ will prevent the class from being inherited.

03. Can you allow a class to be inherited, but prevent the method from being over-ridden?
Ans : Yes. Just leave the class public and make the method sealed.

04. What’s an abstract class?
Ans : A class that cannot be instantiated. An abstract class is a class that must be inherited and have the
methods overridden. An abstract class is essentially a blueprint for a class without any implementation.

05. When do you absolutely have to declare a class as abstract?
1. When the class itself is inherited from an abstract class, but not all base abstract methods have been
overridden.
2. When at least one of the methods in the class is abstract.

06. What is an interface class?
Ans : Interfaces, like classes, define a set of properties, methods, and events. But unlike classes, interfaces do
not provide implementation. They are implemented by classes, and defined as separate entities from classes.

07. Why can’t you specify the accessibility modifier for methods inside the interface?
Ans : They all must be public, and are therefore public by default.
08. Can you inherit multiple interfaces?
Ans : Yes. .NET does support multiple interfaces.

09. What happens if you inherit multiple interfaces and they have conflicting method names?
Ans : It‘s up to you to implement the method inside your own class, so implementation is left entirely up to
you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces
expect      different     data,    but     as      far      as       compiler   cares     you‘re       okay.
To Do: Investigate

10. What’s the difference between an interface and abstract class?
Ans : In an interface class, all methods are abstract - there is no implementation. In an abstract class some
methods can be concrete. In an interface class, no accessibility modifiers are allowed. An abstract class may
have accessibility modifiers.


11. What is the difference between a Struct and a Class?
Structs are value-type variables and are thus saved on the stack, additional overhead but faster retrieval.
Another difference is that structs cannot inherit.




                            Method and Property Questions:


01. What’s the implicit name of the parameter that gets passed into the set method/property of a
class?
Ans : Value. The data type of the value parameter is defined by whatever data type the property is declared
as.

02.    What    does     the    keyword      “virtual”     declare     for    a    method      or    property?
Ans : The method or property can be overridden.

03.     How       is     method       overriding      different     from       method        overloading?
Ans : When overriding a method, you change the behavior of the method for the derived class. Overloading a
method simply involves having another method with the same name within the class.

04. Can you declare an override method to be static if the original method is not static?
Ans : No. The signature of the virtual method must remain the same. (Note: Only the keyword virtual is
changed to keyword override)

05. What are the different ways a method can be overloaded?
Ans : Different parameter data types, different number of parameters, different order of parameters.

06. If a base class has a number of overloaded constructors, and an inheriting class has a number
of overloaded constructors; can you enforce a call from an inherited constructor to a specific base
constructor?
Ans : Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in
the overloaded constructor definition inside the inherited class.




                                     Events and Delegates:

01. What’s a delegate?
Ans : A delegate object encapsulates a reference to a method.

02. What’s a multicast delegate?
Ans : A delegate that has multiple handlers assigned to it. Each assigned handler (method) is called.
                             XML Documentation Questions:


01. Is XML case-sensitive?
Ans : Yes.

02. What’s the difference between // comments, /* */ comments and /// comments?
Ans : Single-line comments, multi-line comments, and XML documentation comments.

03. How do you generate documentation from the C# file commented properly with a command-
line compiler?
Ans : Compile it with the /doc switch.




                          Debugging and Testing Questions:



01. What debugging tools come with the .NET SDK?
Ans : 1. CorDBG – command-line debugger. To use CorDbg, you must compile the original C# file using the
/debug                                                                                          switch.
2. DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR.

02. What does assert() method do?
Ans : In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if
the condition is false. The program proceeds without any interruption if the condition is true.

03.     What’s    the    difference   between      the     Debug       class    and      Trace    class?
Ans : Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and
release builds.

04. Why are there five tracing levels in System.Diagnostics.TraceSwitcher?
Ans : The tracing dumps can be quite verbose. For applications that are constantly running you run the risk of
overloading the machine and the hard drive. Five levels range from None to Verbose, allowing you to fine-
tune the tracing activities.

05. Where is the output of TextWriterTraceListener redirected?
Ans : To the Console or a text file depending on the parameter passed to the constructor.

06. How do you debug an ASP.NET Web application?
Ans : Attach the aspnet_wp.exe process to the DbgClr debugger.

07. What are three test cases you should go through in unit testing?
Ans : 1.     Positive test cases (correct data, correct output).
2.Negative test cases (broken or missing data, proper handling).
3. Exception test cases (exceptions are thrown and caught properly).

08. Can you change the value of a variable while debugging                             a    C#   application?
Ans : Yes. If you are debugging via Visual Studio.NET, just go to Immediate window.
                           ADO.NET and Database Questions:


01.    What      is   the    role    of    the   DataReader      class   in   ADO.NET      connections?
Ans : It returns a read-only, forward-only rowset from the data source. A DataReader provides fast access
when a forward-only sequential read is needed.

02. What are advantages and disadvantages of Microsoft-provided data provider classes in
ADO.NET?
Ans : SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from
Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and
Informix. OLE-DB.NET is a .NET layer on top of the OLE layer, so it‘s not as fastest and efficient as
SqlServer.NET.

03. What is the wildcard character in SQL?
Ans : Let‘s say you want to query database with LIKE for all employees whose name starts with La. The
wildcard character is %, the proper query with LIKE would involve ‗La%‘.

04. Explain ACID rule of thumb for transactions.
Ans : A transaction must be:
1.     Atomic - it is one unit of work and does not dependent on previous and following transactions.
2.     Consistent - data is either committed or roll back, no ―in-between‖ case where something has been
updated and something hasn‘t.
3.       Isolated - no transaction sees the intermediate results of the current transaction).
4.     Durable - the values persist if the data had been committed even if the system crashes right after.

05. What connections does Microsoft SQL Server support?
Ans : Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server
username and password).

06. Between Windows Authentication and SQL Server Authentication, which one is trusted and
which one is untrusted?
Ans : Windows Authentication is trusted because the username and password are checked with the Active
Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the
transaction.


07. What does the Initial Catalog parameter define in the connection string?
Ans : The database name to connect to.

08.    What         does    the   Dispose      method        do       with     the     connection       object?
Ans : Deletes it from the memory.
To Do: answer better. The current answer is not entirely correct.

09. What is a pre-requisite for connection pooling?
Ans : Multiple processes must agree that they will share the same connection, where every parameter is the
same, including the security settings. The connection string must be identical.



10. Explain what a diffgram is and its usage ? A DiffGram is an XML format that is used to identify current
and original versions of data elements. The DataSet uses the DiffGram format to load and persist its contents,
and to serialize its contents for transport across a network connection. When a DataSet is written as a
DiffGram, it populates the DiffGram with all the necessary information to accurately recreate the contents,
though not the schema, of the DataSet, including column values from both the Original and Current row
versions, row error information, and row order.

When sending and retrieving a DataSet from an XML Web service, the DiffGram format is implicitly used.
Additionally, when loading the contents of a DataSet from XML using the ReadXml method, or when writing the
contents of a DataSet in XML using the WriteXml method, you can select that the contents be read or written
as a DiffGram.
The DiffGram format is divided into three sections: the current data, the original (or "before") data, and an
errors section, as shown in the following example.

<?xml version="1.0"?>
<diffgr:diffgram
      xmlns:msdata="urn:schemas-microsoft-com:xml-msdata"
      xmlns:diffgr="urn:schemas-microsoft-com:xml-diffgram-v1"
      xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <DataInstance>
  </DataInstance>

 <diffgr:before>
 </diffgr:before>

 <diffgr:errors>
 </diffgr:errors>
</diffgr:diffgram>

The DiffGram format consists of the following blocks of data:

<DataInstance>
The name of this element, DataInstance, is used for         explanation purposes in this documentation. A
DataInstance element represents a DataSet or a row of a     DataTable. Instead of DataInstance, the element
would contain the name of the DataSet or DataTable. This    block of the DiffGram format contains the current
data, whether it has been modified or not. An element, or   row, that has been modified is identified with the
diffgr:hasChanges annotation.

<diffgr:before>
This block of the DiffGram format contains the original version of a row. Elements in this block are matched to
elements in the DataInstance block using the diffgr:id annotation.

<diffgr:errors>
This block of the DiffGram format contains error information for a particular row in the DataInstance block.
Elements in this block are matched to elements in the DataInstance block using the diffgr:id annotation.

Which method do you invoke on the DataAdapter control to load your generated dataset with data? You have
to use the Fill method of the DataAdapter control and pass the dataset object as an argument to load the
generated data.

11. Can you edit data in the Repeater control?
NO.

12. Which are the different IsolationLevels ?
Following are the various IsolationLevels:


       Serialized Data read by a current transaction cannot be changed by another transaction until the
        current transaction finishes. No new data can be inserted that would affect the current transaction.
        This is the safest isolation level and is the default.
       Repeatable Read Data read by a current transaction cannot be changed by another transaction until
        the current transaction finishes. Any type of new data can be inserted during a transaction.
       Read Committed A transaction cannot read data that is being modified by another transaction that
        has not committed. This is the default isolation level in Microsoft® SQL Server.
       Read Uncommitted A transaction can read any data, even if it is being modified by another
        transaction. This is the least safe isolation level but allows the highest concurrency.
       Any     Any isolation level is supported. This setting is most commonly used by downstream
        components to avoid conflicts. This setting is useful because any downstream component must be
        configured with an isolation level that is equal to or less than the isolation level of its immediate
        upstream component. Therefore, a downstream component that has its isolation level configured as
         Any always uses the same isolation level that its immediate upstream component uses. If the root
         object in a transaction has its isolation level configured to Any, its isolation level becomes Serialized.

13. How xml files and be read and write using dataset?.
DataSet exposes method like ReadXml and WriteXml to read and write xml

14. What are the different rowversions available?
There are four types of Rowversions.
Current:
The current values for the row. This row version does not exist for rows with a RowState of Deleted.

Default : The row the default version for the current DataRowState. For a DataRowState value of Added,
Modified or Current, the default version is Current. For a DataRowState of Deleted, the version is Original. For
a DataRowState value of Detached, the version is Proposed.

Original:
The row contains its original values.

Proposed:
The proposed values for the row. This row version exists during an edit operation on a row, or for a row that is
not part of a DataRowCollection

15. Explain acid properties?. The term ACID conveys the role transactions play in mission-critical
applications. Coined by transaction processing pioneers, ACID stands for atomicity, consistency, isolation, and
durability.

These properties ensure predictable behavior, reinforcing the role of transactions as all-or-none propositions
designed to reduce the management load when there are many variables.

Atomicity
A transaction is a unit of work in which a series of operations occur between the BEGIN TRANSACTION and
END TRANSACTION statements of an application. A transaction executes exactly once and is atomic — all the
work is done or none of it is.

Operations associated with a transaction usually share a common intent and are interdependent. By
performing only a subset of these operations, the system could compromise the overall intent of the
transaction. Atomicity eliminates the chance of processing a subset of operations.

Consistency
A transaction is a unit of integrity because it preserves the consistency of data, transforming one consistent
state of data into another consistent state of data.

Consistency requires that data bound by a transaction be semantically preserved. Some of the responsibility
for maintaining consistency falls to the application developer who must make sure that all known integrity
constraints are enforced by the application. For example, in developing an application that transfers money,
you should avoid arbitrarily moving decimal points during the transfer.

Isolation
A transaction is a unit of isolation — allowing concurrent transactions to behave as though each were the only
transaction running in the system.

Isolation requires that each transaction appear to be the only transaction manipulating the data store, even
though other transactions may be running at the same time. A transaction should never see the intermediate
stages of another transaction.

Transactions attain the highest level of isolation when they are serializable. At this level, the results obtained
from a set of concurrent transactions are identical to the results obtained by running each transaction serially.
Because a high degree of isolation can limit the number of concurrent transactions, some applications reduce
the isolation level in exchange for better throughput.
Durability
A transaction is also a unit of recovery. If a transaction succeeds, the system guarantees that its updates will
persist, even if the computer crashes immediately after the commit. Specialized logging allows the system's
restart procedure to complete unfinished operations, making the transaction durable.



16. Whate are different types of Commands available with DataAdapter ?
The SqlDataAdapter has SelectCommand, InsertCommand, DeleteCommand and UpdateCommand

17. What is a Dataset? Datasets are the result of bringing together ADO and XML. A dataset contains one or
more data of tabular XML, known as DataTables, these data can be treated separately, or can have
relationships defined between them. Indeed these relationships give you ADO data SHAPING without needing
to master the SHAPE language, which many people are not comfortable with.

The dataset is a disconnected in-memory cache database. The dataset object model looks like this:

Dataset
 DataTableCollection
 DataTable
 DataView
 DataRowCollection
  DataRow
 DataColumnCollection
  DataColumn
 ChildRelations
 ParentRelations
 Constraints
 PrimaryKey
DataRelationCollection

Let‘s take a look at each of these:

DataTableCollection: As we say that a DataSet is an in-memory database. So it has this collection, which holds
data from multiple tables in a single DataSet object.

DataTable: In the DataTableCollection, we have DataTable objects, which represents the individual tables of
the dataset.

DataView: The way we have views in database, same way we can have DataViews. We can use these
DataViews to do Sort, filter data.

DataRowCollection: Similar to DataTableCollection, to represent each row in each Table we have
DataRowCollection.

DataRow: To represent each and every row of the DataRowCollection, we have DataRows.

DataColumnCollection: Similar to DataTableCollection, to represent each column in each Table we have
DataColumnCollection.

DataColumn: To represent each and every Column of the DataColumnCollection, we have DataColumn.

PrimaryKey: Dataset defines Primary key for the table and the primary key validation will take place without
going to the database.

Constraints:   We      can   define    various    constraints   on    the    Tables,  and   can    use
Dataset.Tables(0).enforceConstraints. This will execute all the constraints, whenever we enter data in
DataTable.

DataRelationCollection: as we know that we can have more than 1 table in the dataset, we can also define
relationship between these tables using this collection and maintain a parent-child relationship.
18.     Explain      the      ADO       .   Net    Architecture        (     .Net     Data       Provider)
ADO.Net is the data access model for .Net –based applications. It can be used to access relational database
systems such as SQL SERVER 2000, Oracle, and many other data sources for which there is an OLD DB or
ODBC provider. To a certain extent, ADO.NET represents the latest evolution of ADO technology. However,
ADO.NET introduces some major changes and innovations that are aimed at the loosely coupled and inherently
disconnected – nature of web applications.

A .Net Framework data provider is used to connecting to a database, executing commands, and retrieving
results. Those results are either processed directly, or placed in an ADO.NET DataSet in order to be exposed to
the user in an ad-hoc manner, combined with data from multiple sources, or remoted between tiers. The .NET
Framework data provider is designed to be lightweight, creating a minimal layer between the data source and
your code, increasing performance without sacrificing functionality.

Following are the 4 core objects of .Net Framework Data provider:


       Connection: Establishes a connection to a specific data source
       Command: Executes a command against a data source. Exposes Parameters and can execute within
        the scope of a Transaction from a Connection.
       DataReader: Reads a forward-only, read-only stream of data from a data source.
       DataAdapter: Populates a DataSet and resolves updates with the data source.

The .NET Framework includes the .NET Framework Data Provider for SQL Server (for Microsoft SQL Server
version 7.0 or later), the .NET Framework Data Provider for OLE DB, and the .NET Framework Data Provider
for ODBC.

The .NET Framework Data Provider for SQL Server: The .NET Framework Data Provider for SQL Server uses
its own protocol to communicate with SQL Server. It is lightweight and performs well because it is optimized to
access a SQL Server directly without adding an OLE DB or Open Database Connectivity (ODBC) layer. The
following illustration contrasts the .NET Framework Data Provider for SQL Server with the .NET Framework
Data Provider for OLE DB. The .NET Framework Data Provider for OLE DB communicates to an OLE DB data
source through both the OLE DB Service component, which provides connection pooling and transaction
services, and the OLE DB Provider for the data source

The .NET Framework Data Provider for OLE DB: The .NET Framework Data Provider for OLE DB uses native
OLE DB through COM interoperability to enable data access. The .NET Framework Data Provider for OLE DB
supports both local and distributed transactions. For distributed transactions, the .NET Framework Data
Provider for OLE DB, by default, automatically enlists in a transaction and obtains transaction details from
Windows 2000 Component Services.

The .NET Framework Data Provider for ODBC: The .NET Framework Data Provider for ODBC uses native ODBC
Driver Manager (DM) through COM interoperability to enable data access. The ODBC data provider supports
both local and distributed transactions. For distributed transactions, the ODBC data provider, by default,
automatically enlists in a transaction and obtains transaction details from Windows 2000 Component Services.

The .NET Framework Data Provider for Oracle: The .NET Framework Data Provider for Oracle enables data
access to Oracle data sources through Oracle client connectivity software. The data provider supports Oracle
client software version 8.1.7 and later. The data provider supports both local and distributed transactions (the
data provider automatically enlists in existing distributed transactions, but does not currently support the
EnlistDistributedTransaction method).

The .NET Framework Data Provider for Oracle requires that Oracle client software (version 8.1.7 or later) be
installed on the system before you can use it to connect to an Oracle data source.
.NET Framework Data Provider for Oracle classes are located in the System.Data.OracleClient namespace and
are contained in the System.Data.OracleClient.dll assembly. You will need to reference both the
System.Data.dll and the System.Data.OracleClient.dll when compiling an application that uses the data
provider.
Choosing a .NET Framework Data Provider

.NET Framework Data Provider for SQL Server: Recommended for middle-tier applications using Microsoft SQL
Server 7.0 or later. Recommended for single-tier applications using Microsoft Data Engine (MSDE) or Microsoft
SQL                       Server                       7.0                       or                     later.
Recommended over use of the OLE DB Provider for SQL Server (SQLOLEDB) with the .NET Framework Data
Provider for OLE DB. For Microsoft SQL Server version 6.5 and earlier, you must use the OLE DB Provider for
SQL Server with the .NET Framework Data Provider for OLE DB.

.NET Framework Data Provider for OLE DB: Recommended for middle-tier applications using Microsoft SQL
Server 6.5 or earlier, or any OLE DB provider. For Microsoft SQL Server 7.0 or later, the .NET Framework Data
Provider for SQL Server is recommended. Recommended for single-tier applications using Microsoft Access
databases. Use of a Microsoft Access database for a middle-tier application is not recommended.

.NET Framework Data Provider for ODBC: Recommended for middle-tier applications using ODBC data sources.
Recommended for single-tier applications using ODBC data sources.

.NET Framework Data Provider for Oracle: Recommended for middle-tier applications using Oracle data
sources. Recommended for single-tier applications using Oracle data sources. Supports Oracle client software
version 8.1.7 and later. The .NET Framework Data Provider for Oracle classes are located in the
System.Data.OracleClient namespace and are contained in the System.Data.OracleClient.dll assembly. You
need to reference both the System.Data.dll and the System.Data.OracleClient.dll when compiling an
application that uses the data provider.

19. Can you explain the difference between an ADO.NET Dataset and an ADO Recordset? Let‘s take a
look at the differences between ADO Recordset and ADO.Net DataSet:

1. Table Collection: ADO Recordset provides the ability to navigate through a single table of information. That
table would have been formed with a join of multiple tables and returning columns from multiple tables.
ADO.NET DataSet is capable of holding instances of multiple tables. It has got a Table Collection, which holds
multiple tables in it. If the tables are having a relation, then it can be manipulated on a Parent-Child
relationship. It has the ability to support multiple tables with keys, constraints and interconnected
relationships. With this ability the DataSet can be considered as a small, in-memory relational database cache.

2. Navigation: Navigation in ADO Recordset is based on the cursor mode. Even though it is specified to be a
client-side Recordset, still the navigation pointer will move from one location to another on cursor model only.
ADO.NET DataSet is an entirely offline, in-memory, and cache of data. All of its data is available all the time.
At any time, we can retrieve any row or column, constraints or relation simply by accessing it either ordinarily
or by retrieving it from a name-based collection.

3. Connectivity Model: The ADO Recordset was originally designed without the ability to operate in a
disconnected environment. ADO.NET DataSet is specifically designed to be a disconnected in-memory
database. ADO.NET DataSet follows a pure disconnected connectivity model and this gives it much more
scalability and versatility in the amount of things it can do and how easily it can do that.

4. Marshalling and Serialization: In COM, through Marshalling, we can pass data from 1 COM component to
another component at any time. Marshalling involves copying and processing data so that a complex type can
appear to the receiving component the same as it appeared to the sending component. Marshalling is an
expensive operation. ADO.NET Dataset and DataTable components support Remoting in the form of XML
serialization. Rather than doing expensive Marshalling, it uses XML and sent data across boundaries.

5. Firewalls and DCOM and Remoting: Those who have worked with DCOM know that how difficult it is to
marshal a DCOM component across a router. People generally came up with workarounds to solve this issue.
ADO.NET DataSet uses Remoting, through which a DataSet / DataTable component can be serialized into XML,
sent across the wire to a new AppDomain, and then Desterilized back to a fully functional DataSet. As the
DataSet is completely disconnected, and it has no dependency, we lose absolutely nothing by serializing and
transferring it through Remoting.



20. How do you handle data concurrency in .NET ? One of the key features of the ADO.NET DataSet is
that it can be a self-contained and disconnected data store. It can contain the schema and data from several
rowsets in DataTable objects as well as information about how to relate the DataTable objects-all in memory.
The DataSet neither knows nor cares where the data came from, nor does it need a link to an underlying data
source. Because it is data source agnostic you can pass the DataSet around networks or even serialize it to
XML and pass it across the Internet without losing any of its features. However, in a disconnected model,
concurrency obviously becomes a much bigger problem than it is in a connected model.
In this column, I'll explore how ADO.NET is equipped to detect and handle concurrency violations. I'll begin by
discussing scenarios in which concurrency violations can occur using the ADO.NET disconnected model. Then I
will walk through an ASP.NET application that handles concurrency violations by giving the user the choice to
overwrite the changes or to refresh the out-of-sync data and begin editing again. Because part of managing an
optimistic concurrency model can involve keeping a timestamp (rowversion) or another type of flag that
indicates when a row was last updated, I will show how to implement this type of flag and how to maintain its
value after each database update.



Is Your Glass Half Full?

There are three common techniques for managing what happens when users try to modify the same data at
the same time: pessimistic, optimistic, and last-in wins. They each handle concurrency issues differently.

The pessimistic approach says: "Nobody can cause a concurrency violation with my data if I do not let them
get at the data while I have it." This tactic prevents concurrency in the first place but it limits scalability
because it prevents all concurrent access. Pessimistic concurrency generally locks a row from the time it is
retrieved until the time updates are flushed to the database. Since this requires a connection to remain open
during the entire process, pessimistic concurrency cannot successfully be implemented in a disconnected
model like the ADO.NET DataSet, which opens a connection only long enough to populate the DataSet then
releases and closes, so a database lock cannot be held.

Another technique for dealing with concurrency is the last-in wins approach. This model is pretty
straightforward and easy to implement-whatever data modification was made last is what gets written to the
database. To implement this technique you only need to put the primary key fields of the row in the UPDATE
statement's WHERE clause. No matter what is changed, the UPDATE statement will overwrite the changes with
its own changes since all it is looking for is the row that matches the primary key values. Unlike the pessimistic
model, the last-in wins approach allows users to read the data while it is being edited on screen. However,
problems can occur when users try to modify the same data at the same time because users can overwrite
each other's changes without being notified of the collision. The last-in wins approach does not detect or notify
the user of violations because it does not care. However the optimistic technique does detect violations.

In optimistic concurrency models, a row is only locked during the update to the database. Therefore the data
can be retrieved and updated by other users at any time other than during the actual row update operation.
Optimistic concurrency allows the data to be read simultaneously by multiple users and blocks other users less
often than its pessimistic counterpart, making it a good choice for ADO.NET. In optimistic models, it is
important to implement some type of concurrency violation detection that will catch any additional attempt to
modify records that have already been modified but not committed. You can write your code to handle the
violation by always rejecting and canceling the change request or by overwriting the request based on some
business rules. Another way to handle the concurrency violation is to let the user decide what to do. The
sample application that is shown in Figure 1 illustrates some of the options that can be presented to the user
in the event of a concurrency violation.

Where Did My Changes Go?

When users are likely to overwrite each other's changes, control mechanisms should be put in place.
Otherwise, changes could be lost. If the technique you're using is the last-in wins approach, then these types
of overwrites are entirely possible.For example, imagine Julie wants to edit an employee's last name to correct
the spelling. She navigates to a screen which loads the employee's information into a DataSet and has it
presented to her in a Web page. Meanwhile, Scott is notified that the same employee's phone extension has
changed. While Julie is correcting the employee's last name, Scott begins to correct his extension. Julie saves
her changes first and then Scott saves his.Assuming that the application uses the last-in wins approach and
updates the row using a SQL WHERE clause containing only the primary key's value, and assuming a change
to one column requires the entire row to be updated, neither Julie nor Scott may immediatelyrealize the
concurrency issue that just occurred. In this particular situation, Julie's changes were overwritten by Scott's
changes because he saved last, and the last name reverted to the misspelled version.

So as you can see, even though the users changed different fields, their changes collided and caused Julie's
changes to be lost. Without some sort of concurrency detection and handling, these types of overwrites can
occur and even go unnoticed.When you run the sample application included in this column's download, you
should open two separate instances of Microsoft® Internet Explorer. When I generated the conflict, I opened
two instances to simulate two users with two separate sessions so that a concurrency violation would occur in
the sample application. When you do this, be careful not to use Ctrl+N because if you open one instance and
then use the Ctrl+N technique to open another instance, both windows will share the same session.

Detecting Violations

The concurrency violation reported to the user in Figure 1 demonstrates what can happen when multiple users
edit the same data at the same time. In Figure 1, the user attempted to modify the first name to "Joe" but
since someone else had already modified the last name to "Fuller III," a concurrency violation was detected
and reported. ADO.NET detects a concurrency violation when a DataSet containing changed values is passed to
a SqlDataAdapter's Update method and no rows are actually modified. Simply using the primary key (in this
case the EmployeeID) in the UPDATE statement's WHERE clause will not cause a violation to be detected
because it still updates the row (in fact, this technique has the same outcome as the last-in wins technique).
Instead, more conditions must be specified in the WHERE clause in order for ADO.NET to detect the violation.

The key here is to make the WHERE clause explicit enough so that it not only checks the primary key but that
it also checks for another appropriate condition. One way to accomplish this is to pass in all modifiable fields to
the WHERE clause in addition to the primary key. For example, the application shown in Figure 1 could have its
UPDATE statement look like the stored procedure that's shown in Figure 2.

Notice that in the code in Figure 2 nullable columns are also checked to see if the value passed in is NULL. This
technique is not only messy but it can be difficult to maintain by hand and it requires you to test for a
significant number of WHERE conditions just to update a row. This yields the desired result of only updating
rows where none of the values have changed since the last time the user got the data, but there are other
techniques that do not require such a huge WHERE clause.

Another way to make sure that the row is only updated if it has not been modified by another user since you
got the data is to add a timestamp column to the table. The SQL Server(tm) TIMESTAMP datatype
automatically updates itself with a new value every time a value in its row is modified. This makes it a very
simple and convenient tool to help detect concurrency violations.

A third technique is to use a DATETIME column in which to track changes to its row. In my sample application I
added a column called LastUpdateDateTime to the Employees table.

ALTER TABLE Employees ADD LastUpdateDateTime DATETIME

There I update the value of the LastUpdateDateTime field automatically in the UPDATE stored procedure using
the built-in SQL Server GETDATE function.

The binary TIMESTAMP column is simple to create and use since it automatically regenerates its value each
time its row is modified, but since the DATETIME column technique is easier to display on screen and
demonstrate when the change was made, I chose it for my sample application. Both of these are solid choices,
but I prefer the TIMESTAMP technique since it does not involve any additional code to update its value.

Retrieving Row Flags

One of the keys to implementing concurrency controls is to update the timestamp or datetime field's value
back into the DataSet. If the same user wants to make more modifications, this updated value is reflected in
the DataSet so it can be used again. There are a few different ways to do this. The fastest is using output
parameters within the stored procedure. (This should only return if @@ROWCOUNT equals 1.) The next fastest
involves selecting the row again after the UPDATE within the stored procedure. The slowest involves selecting
the row from another SQL statement or stored procedure from the SqlDataAdapter's RowUpdated event.

I prefer to use the output parameter technique since it is the fastest and incurs the least overhead. Using the
RowUpdated event works well, but it requires me to make a second call from the application to the database.
The following code snippet adds an output parameter to the SqlCommand object that is used to update the
Employee information:

oUpdCmd.Parameters.Add(new SqlParameter("@NewLastUpdateDateTime",

 SqlDbType.DateTime, 8, ParameterDirection.Output,
    false, 0, 0, "LastUpdateDateTime", DataRowVersion.Current, null));

oUpdCmd.UpdatedRowSource = UpdateRowSource.OutputParameters;

The output parameter has its sourcecolumn and sourceversion arguments set to point the output parameter's
return value back to the current value of the LastUpdateDateTime column of the DataSet. This way the
updated DATETIME value is retrieved and can be returned to the user's .aspx page.

Saving Changes

Now that the Employees table has the tracking field (LastUpdateDateTime) and the stored procedure has been
created to use both the primary key and the tracking field in the WHERE clause of the UPDATE statement, let's
take a look at the role of ADO.NET. In order to trap the event when the user changes the values in the
textboxes, I created an event handler for the TextChanged event for each TextBox control:

private void txtLastName_TextChanged(object sender, System.EventArgs e)

{

     // Get the employee DataRow (there is only 1 row, otherwise I could

     // do a Find)

     dsEmployee.EmployeeRow oEmpRow =

          (dsEmployee.EmployeeRow)oDsEmployee.Employee.Rows[0];

     oEmpRow.LastName = txtLastName.Text;

     // Save changes back to Session

     Session["oDsEmployee"] = oDsEmployee;

}

This event retrieves the row and sets the appropriate field's value from the TextBox. (Another way of getting
the changed values is to grab them when the user clicks the Save button.) Each TextChanged event executes
after the Page_Load event fires on a postback, so assuming the user changed the first and last names, when
the user clicks the Save button, the events could fire in this order: Page_Load, txtFirstName_TextChanged,
txtLastName_TextChanged, and btnSave_Click.

The Page_Load event grabs the row from the DataSet in the Session object; the TextChanged events update
the DataRow with the new values; and the btnSave_Click event attempts to save the record to the database.
The btnSave_Click event calls the SaveEmployee method (shown in Figure 3) and passes it a bLastInWins
value of false since we want to attempt a standard save first. If the SaveEmployee method detects that
changes were made to the row (using the HasChanges method on the DataSet, or alternatively using the
RowState property on the row), it creates an instance of the Employee class and passes the DataSet to its
SaveEmployee method. The Employee class could live in a logical or physical middle tier. (I wanted to make
this a separate class so it would be easy to pull the code out and separate it from the presentation logic.)

Notice that I did not use the GetChanges method to pull out only the modified rows and pass them to the
Employee object's Save method. I skipped this step here since there is only one row. However, if there were
multiple rows in the DataSet's DataTable, it would be better to use the GetChanges method to create a
DataSet that contains only the modified rows.

If the save succeeds, the Employee.SaveEmployee method returns a DataSet containing the modified row and
its newly updated row version flag (in this case, the LastUpdateDateTime field's value). This DataSet is then
merged into the original DataSet so that the LastUpdateDateTime field's value can be updated in the original
DataSet. This must be done because if the user wants to make more changes she will need the current values
from the database merged back into the local DataSet and shown on screen. This includes the
LastUpdateDateTime value which is used in the WHERE clause. Without this field's current value, a false
concurrency violation would occur.

Reporting Violations

If a concurrency violation occurs, it will bubble up and be caught by the exception handler shown in Figure 3 in
the catch block for DBConcurrencyException. This block calls the FillConcurrencyValues method, which displays
both the original values in the DataSet that were attempted to be saved to the database and the values
currently in the database. This method is used merely to show the user why the violation occurred. Notice that
the exDBC variable is passed to the FillConcurrencyValues method. This instance of the special database
concurrency exception class (DBConcurrencyException) contains the row where the violation occurred. When a
concurrency violation occurs, the screen is updated to look like Figure 1.

The DataSet not only stores the schema and the current data, it also tracks changes that have been made to
its data. It knows which rows and columns have been modified and it keeps track of the before and after
versions of these values. When accessing a column's value via the DataRow's indexer, in addition to the
column index you can also specify a value using the DataRowVersion enumerator. For example, after a user
changes the value of the last name of an employee, the following lines of C# code will retrieve the original and
current values stored in the LastName column:

string sLastName_Before = oEmpRow["LastName", DataRowVersion.Original];

string sLastName_After = oEmpRow["LastName", DataRowVersion.Current];

The FillConcurrencyValues method uses the row from the DBConcurrencyException and gets a fresh copy of
the same row from the database. It then displays the values using the DataRowVersion enumerators to show
the original value of the row before the update and the value in the database alongside the current values in
the textboxes.

User's Choice

Once the user has been notified of the concurrency issue, you could leave it up to her to decide how to handle
it. Another alternative is to code a specific way to deal with concurrency, such as always handling the
exception to let the user know (but refreshing the data from the database). In this sample application I let the
user decide what to do next. She can either cancel changes, cancel and reload from the database, save
changes, or save anyway.

The option to cancel changes simply calls the RejectChanges method of the DataSet and rebinds the DataSet
to the controls in the ASP.NET page. The RejectChanges method reverts the changes that the user made back
to its original state by setting all of the current field values to the original field values. The option to cancel
changes and reload the data from the database also rejects the changes but additionally goes back to the
database via the Employee class in order to get a fresh copy of the data before rebinding to the control on the
ASP.NET page.

The option to save changes attempts to save the changes but will fail if a concurrency violation is encountered.
Finally, I included a "save anyway" option. This option takes the values the user attempted to save and uses
the last-in wins technique, overwriting whatever is in the database. It does this by calling a different command
object associated with a stored procedure that only uses the primary key field (EmployeeID) in the WHERE
clause of the UPDATE statement. This technique should be used with caution as it will overwrite the record.

If you want a more automatic way of dealing with the changes, you could get a fresh copy from the database.
Then overwrite just the fields that the current user modified, such as the Extension field. That way, in the
example I used the proper LastName would not be overwritten. Use this with caution as well, however,
because if the same field was modified by both users, you may want to just back out or ask the user what to
do next. What is obvious here is that there are several ways to deal with concurrency violations, each of which
must be carefully weighed before you decide on the one you will use in your application.
Wrapping It Up

Setting the SqlDataAdapter's ContinueUpdateOnError property tells the SqlDataAdapter to either throw an
exception when a concurrency violation occurs or to skip the row that caused the violation and to continue with
the remaining updates. By setting this property to false (its default value), it will throw an exception when it
encounters a concurrency violation. This technique is ideal when only saving a single row or when you are
attempting to save multiple rows and want them all to commit or all to fail.

I have split the topic of concurrency violation management into two parts. Next time I will focus on what to do
when multiple rows could cause concurrency violations. I will also discuss how the DataViewRowState
enumerators can be used to show what changes have been made to a DataSet.

21.      How       you       will     set      the      datarelation       between         two      columns?
ADO.NET provides DataRelation object to set relation between two columns.It helps to enforce the following
constraints,a unique constraint, which guarantees that a column in the table contains no duplicates and a
foreign-key constraint,which can be used to maintain referential integrity.A unique constraint is implemented
either by simply setting the Unique property of a data column to true, or by adding an instance of the
UniqueConstraint class to the DataRelation object's ParentKeyConstraint. As part of the foreign-key constraint,
you can specify referential integrity rules that are applied at three points,when a parent record is
updated,when a parent record is deleted and when a change is accepted or rejected.




                                      Assembly Questions:


01. How is the DLL Hell problem solved in .NET?
Ans : Assembly versioning allows the application to specify not only the library it needs to run (which was
available under Win32), but also the version of the assembly.

02. What are the ways to deploy an assembly?
Ans : An MSI installer, a CAB archive, and XCOPY command.

03. What is a satellite assembly?
Ans : When you write a multilingual or multi-cultural application in .NET, and want to distribute the core
application separately from the localized modules, the localized assemblies that modify the core application are
called satellite assemblies.

04. What namespaces are necessary to create a localized application?
Ans : System.Globalization and System.Resources.

05. What is the smallest unit of execution in .NET?
Ans : an Assembly.

06. When should you call the garbage collector in .NET?
Ans : As a good rule, you should not call the garbage collector. However, you could call the garbage collector
when you are done using a large object (or set of objects) to force the garbage collector to dispose of those
very large objects from memory. However, this is usually not a good practice.


07. How do you convert a value-type to a reference-type?
Ans : Use Boxing.

08. What happens in memory when you Box and Unbox a value-type?
Ans : Boxing converts a value-type to a reference-type, thus storing the object on the heap.          Unboxing
converts a reference-type to a value-type, thus storing the value on the stack.
                                    .NET FrameWork FAQ's


01. When was .NET announced?
Ans : Bill Gates delivered a keynote at Forum 2000, held June 22, 2000, outlining the .NET 'vision'. The July
2000 PDC had a number of sessions on .NET technology, and delegates were given CDs containing a pre-
release version of the .NET framework/SDK and Visual Studio.NET.

02. When was the first version of .NET released?
Ans : The final version of the 1.0 SDK and runtime was made publicly available around 6pm PST on 15-Jan-
2002. At the same time, the final version of Visual Studio.NET was made available to MSDN subscribers.

03. What platforms does the .NET Framework run on?
Ans : The runtime supports Windows XP, Windows 2000, NT4 SP6a and Windows ME/98. Windows 95 is not
supported. Some parts of the framework do not work on all platforms - for example, ASP.NET is only
supported on Windows XP and Windows 2000. Windows 98/ME cannot be used for development. IIS is not
supported on Windows XP Home Edition, and so cannot be used to host ASP.NET. However, the ASP.NET Web
Matrix web server does run on XP Home. The Mono project is attempting to implement the .NET framework on
Linux.

04. What is the CLR?
Ans : CLR = Common Language Runtime. The CLR is a set of standard resources that (in theory) any .NET
program can take advantage of, regardless of programming language. Robert Schmidt (Microsoft) lists the
following CLR resources in his MSDN PDC# article:Object-oriented programming model (inheritance,
polymorphism, exception handling, garbage collection) Security model Type system All .NET base classes
 Many .NET framework classes Development, debugging, and profiling tools Execution and code management
 IL-to-native translators and optimizers What this means is that in the .NET world, different programming
languages will be more equal in capability than they have ever been before, although clearly not all languages
will support all CLR services.

05. What is the CTS?
Ans : CTS = Common Type System. This is the range of types that the .NET runtime understands, and
therefore that .NET applications can use. However note that not all .NET languages will support all the types in
the CTS. The CTS is a superset of the CLS.

06. What is the CLS?
Ans : CLS = Common Language Specification. This is a subset of the CTS which all .NET languages are
expected to support. The idea is that any program which uses CLS-compliant types can interoperate with any
.NET program written in any language.
In theory this allows very tight interop between different .NET languages - for example allowing a C# class to
inherit from a VB class.

07. What is IL?
Ans : IL = Intermediate Language. Also known as MSIL (Microsoft Intermediate Language) or CIL (Common
Intermediate Language). All .NET source code (of any language) is compiled to IL. The IL is then converted to
machine code at the point where the software is installed, or at run-time by a Just-In-Time (JIT) compiler.

08. What does 'managed' mean in the .NET context?
Ans : The term 'managed' is the cause of much confusion. It is used in various places within .NET, meaning
slightly different things.Managed code: The .NET framework provides several core run-time services to the
programs that run within it - for example
exception handling and security. For these services to work, the code must provide a minimum level of
information to the runtime.
Such code is called managed code. All C# and Visual Basic.NET code is managed by default. VS7 C++ code is
not managed by default, but the compiler can produce managed code by specifying a command-line switch
(/com+).
Managed data: This is data that is allocated and de-allocated by the .NET runtime's garbage collector. C# and
VB.NET data is always managed. VS7 C++ data is unmanaged by default, even when using the /com+ switch,
but it can be marked as managed using the __gc keyword.Managed classes: This is usually referred to in the
context of Managed Extensions (ME) for C++. When using ME C++, a class can be marked with the __gc
keyword. As the name suggests, this means that the memory for instances of the class is managed by the
garbage collector, but it also means more than that. The class becomes a fully paid-up member of the .NET
community with the benefits and restrictions that brings. An example of a benefit is proper interop with classes
written in other languages - for example, a managed C++ class can inherit from a VB class. An example of a
restriction is that a managed class can only inherit from one base class.

09. What is reflection?
Ans : All .NET compilers produce metadata about the types defined in the modules they produce. This
metadata is packaged along with the module (modules in turn are packaged together in assemblies), and can
be accessed by a mechanism called reflection. The System.Reflection namespace contains classes that can be
used           to        interrogate         the          types        for         a         module/assembly.
Using reflection to access .NET metadata is very similar to using ITypeLib/ITypeInfo to access type library data
in COM, and it is used for similar purposes - e.g. determining data type sizes for marshaling data across
context/process/machine                                                                             boundaries.
Reflection can also be used to dynamically invoke methods (see System.Type.InvokeMember ) , or even
create types dynamically at run-time (see System.Reflection.Emit.TypeBuilder).

10. What is the difference between Finalize and Dispose (Garbage collection) ?
Ans : Class instances often encapsulate control over resources that are not managed by the runtime, such as
window handles (HWND), database connections, and so on. Therefore, you should provide both an explicit and
an implicit way to free those resources. Provide implicit control by implementing the protected Finalize Method
on an object (destructor syntax in C# and the Managed Extensions for C++). The garbage collector calls this
method at some point after there are no longer any valid references to the object. In some cases, you might
want to provide programmers using an object with the ability to explicitly release these external resources
before the garbage collector frees the object. If an external resource is scarce or expensive, better
performance can be achieved if the programmer explicitly releases resources when they are no longer being
used. To provide explicit control, implement the Dispose method provided by the IDisposable Interface. The
consumer of the object should call this method when it is done using the object.
Dispose can be called even if other references to the object are alive. Note that even when you provide explicit
control by way of Dispose, you should provide implicit cleanup using the Finalize method. Finalize provides a
backup to prevent resources from
permanently leaking if the programmer fails to call Dispose.

11. What is Partial Assembly References?
Ans : Full Assembly reference: A full assembly reference includes the assembly's text name, version, culture,
and public key token (if the assembly has a strong name). A full assembly reference is required if you
reference any assembly that is part of the common language runtime or any assembly located in the global
assembly cache.

12. Partial Assembly reference: We can dynamically reference an assembly by providing only partial
information, such as specifying only the assembly name. When you specify a partial assembly reference, the
runtime looks for the assembly only in the application directory. We can make partial references to an
assembly         in         your         code         one         of         the         following     ways:
-> Use a method such as System.Reflection.Assembly.Load and specify only a partial reference. The runtime
checks         for         the          assembly           in         the          application     directory.
-> Use the System.Reflection.Assembly.LoadWithPartialName method and specify only a partial reference. The
runtime checks for the assembly in the application directory and in the global assembly cache

13. Changes to which portion of version number indicates an incompatible change?
Ans : Major or minor. Changes to the major or minor portion of the version number indicate an incompatible
change. Under this convention then, version 2.0.0.0 would be considered incompatible with version 1.0.0.0.
Examples of an incompatible change would be a change to the types of some method parameters or the
removal of a type or method altogether. Build. The Build number is typically used to distinguish between daily
builds or smaller compatible releases. Revision. Changes to the revision number are typically reserved for an
incremental build needed to fix a particular bug. You'll sometimes hear this referred to as the "emergency bug
fix" number in that the revision is what is often changed when a fix to a specific bug is shipped to a customer.



14. How to set the debug mode?

Debug Mode for ASP.NET applications - To set ASP.NET appplication in debugging mode, edit the application's
web.config and assign the "debug" attribute in < compilation > section to "true" as show below:
< configuration >
  < system.web >
    < compilation defaultLanguage="vb" debug="true" / >
....
...
..
< / configuration >

This case-sensitive attribute 'debug tells ASP.NET to generate symbols for dynamically generated files and
enables                                                                                                the
debugger to attach to the ASP.NET application. ASP.NET will detect this change automatically, without the
need to restart the server. Debug Mode for ASP.NET Webservices - Debugging an XML Web service created
with ASP.NET is similar to the debugging an ASP.NET Web application.

15. What is the property available to check if the page posted or not?

Ans : The Page_Load event handler in the page checks for IsPostBack property value, to ascertain whether the
page is posted. The Page.IsPostBack gets a value indicating whether the page is being loaded in response to
the client postback, or it is for the first time. The value of Page.IsPostBack is True, if the page is being loaded
in response to the client postback; while its value is False, when the page is loaded for the first time. The
Page.IsPostBack property facilitates execution of certain routine in Page_Load, only once (for e.g. in Page load,
we need to set default value in controls, when page is loaded for the first time. On post back, we check for
true value for IsPostback value and then invoke server-side code to update data).

16.    Which     are    the     abstract     classes     available   under     system.xml  namespace?
Ans : The System.XML namespace provides XML related processing ability in .NET framework. XmlReader and
XMLWriter are the two abstract classes at the core of .NET Framework XML classes:

1. XmlReader provides a fast, forward-only, read-only cursor for processing an XML document stream.

2. XmlWriter provides an interface for producing XML document streams that conform to the W3C's XML
standards.

Both XmlReader and XmlWriter are abstract base classes, which define the functionality that all derived classes
must support.




17.        Is       it      possible         to        use      multipe        inheritance         in       .net?
Ans : Multiple Inheritance is an ability to inherit from more than one base class i.e. ability of a class to have
more than one superclass, by inheriting from different sources and thus combine separately-defined behaviors
in a single class. There are two types of multiple inheritance: multiple type/interface inheritance and multiple
implementation inheritance. C# & VB.NET supports only multiple type/interface inheritance, i.e. you can derive
an class/interface from multiple interfaces. There is no support for multiple implementation inheritance in
.NET. That means a class can only derived from one class.

18. What are the derived classes from xmlReader and xmlWriter?
Both XmlReader and XmlWriter are abstract base classes, which define the functionality that all derived classes
must support.
There are three concrete implementations of XmlReader:
     1.XmlTextReader
     2.XmlNodeReader
     3.XmlValidatingReader
There are two concrete implementations of XmlWriter:
     1.XmlTextWriter
     2.XmlNodeWriter
XmlTextReader and XmlTextWriter support reading data to/from text-based stream, while XmlNodeReader and
XmlNodeWriter are designed for working with in-memory DOM tree structure. The custom readers and writers
can also be developed to extend the built-in functionality of XmlReader and XmlWriter.

19. What is managed and unmanaged code?

Ans : The .NET framework provides several core run-time services to the programs that run within it - for
example exception handling and security. For these services to work, the code must provide a minimum level
of information to the runtime. i.e., code executing under the control of the CLR is called managed code. For
example, any code written in C# or Visual Basic .NET is managed code. Code that runs outside the CLR is
referred to as "unmanaged code." COM components, ActiveX components, and Win32 API functions are
examples of unmanaged code.

20. How you deploy .NET assemblies?
Ans : One way is simply use xcopy. others are use and the setup projects in .net. and one more way is use of
nontuch deployment.

21. What is Globalizationa and Localization ?
Ans : Globalization is the process of creating an application that meets the needs of users from multiple
cultures. It includes using the correct
currency, date and time format, calendar, writing direction, sorting rules, and other issues. Accommodating
these cultural differences in an application is called localization.Using classes of System.Globalization
namespace, you can set application's current culture.

This can be achieved by using any of the following 3 approaches.
    1.    Detect and redirect
    2.    Run-time adjustment
    3.    Using Satellite assemblies.



22.      Whate       are      Resource       Files     ?      How        are     they       used      in    .NET?
Ans : Resource files are the files containing data that is logically deployed with an application.These files can
contain data in a number of formats including strings, images and persisted objects. It has the main advantage
of If we store data in these files then we don't need to compile these if the data get changed. In .NET we
basically require them storing culture specific informations by localizing application's resources. You can deploy
your resources using satellite assemblies.

23. Difference between Dispose and Finallize method?

Ans : Finalize   method is used to free the memory used by some unmanaged resources like window handles
(HWND). It's     similar to the destructor syntax in C#. The GC calls this method when it founds no more
references to     the object. But, In some cases we may need release the memory used by the resources
explicitely.To   release the memory explicitly we need to implement the Dispose method of IDisposable
interface.

24. What is encapsulation ?

Ans : Encapsulation is the ability to hide the internal workings of an object's behavior and its data. For
instance, let's say you have a object named Bike and this object has a method named start(). When you
create an instance of a Bike object and call its start() method you are not worried about what happens to
accomplish this, you just want to make sure the state of the bike is changed to 'running' afterwards. This kind
of behavior hiding is encapsulation and it makes programming much easier.

25. How can you prevent your class to be inherated further?

Ans : By setting Sealed - Key word

public sealed class Planet
{
         //code goes here
}

class Moon:Planet
 {
    //Not allowed as base class is sealed
 }
26. What is GUID and why we need to use it and in what condition? How this is created.

Ans : A GUID is a 128-bit integer (16 bytes) that can be used across all computers and networks wherever a
unique identifier is required. Such an identifier has a very low probability of being duplicated. Visual Studio
.NET IDE has a utility under the tools menu to generate GUIDs.

27. Why do you need to serialize.?

We need to serialize the object,if you want to pass object from one computer/application domain to
another.Process of converting complex objects into stream of bytes that can be persisted or
transported.Namespace for serialization is System.Runtime.Serialization.The ISerializable interface allows you
to    make       any     class    Serializable..NET  framework       features    2     serializing     method.
1.Binary Serialization 2.XML Serialization

28.               What          is      inline        schema,         how          does       it        works?
Ans : Schemas can be included inside of XML file is called Inline Schemas.This is useful when it is inconvenient
to physically seprate the schema and the XML document.A schema is an XML document that defines the
structure, constraints, data types, and relationships of the elements that constitute the data contained inside
the XML document or in another XML document.Schema can be an external file which uses the XSD or XDR
extension called external schema. Inline schema can take place even when validation is turned off.

29. Describe the advantages of writing a managed code application instead of unmanaged one.
What's involved in certain piece of code being managed?

"Advantage includes automatic garbage collection,memory management,security,type checking,versioning

Managed code is compiled for the .NET run-time environment. It runs in the Common Language Runtime
(CLR), which is the heart of the .NET Framework. The CLR provides services such as security,
memory management, and cross-language integration. Managed applications written to take advantage of the
features of the CLR perform more efficiently and safely, and take better advantage of developers existing
expertise in languages that support the .NET Framework.

Unmanaged code includes all code written before the .NET Framework was introduced—this includes code
written to use COM, native Win32, and Visual Basic 6. Because it does not run inside the .NET environment,
unmanaged code cannot make use of any .NET managed facilities."

30. What are multicast delegates ? give me an example ?
Ans : Delegate that can have more than one element in its invocation List.

using System;
namespace SampleMultiCastDelegate
{
  class MultiCast
  {
    public delegate string strMultiCast(string s);
  }
}



MainClass defines the static methods having same signature as delegate.
using System;

namespace SampleMultiCastDelegate
{
   public class MainClass
  {
    public MainClass()
    {
    }
        public static string Jump(string s)
        {
          Console.WriteLine("Jump");
          return String.Empty;
        }

        public static string Run(string s)
        {
          Console.WriteLine("Run");
          return String.Empty;
        }

        public static string Walk(string s)
        {
          Console.WriteLine("Walk");
          return String.Empty;
        }
    }
}



The Main class:

using System;
using System.Threading;
namespace SampleMultiCastDelegate
{

    public class MainMultiCastDelegate
    {
      public static void Main()
      {
        MultiCast.strMultiCast Run,Walk,Jump;

            MultiCast.strMultiCast   myDelegate;

             ///here mydelegate used the Combine method of System.MulticastDelegate
            ///and the delegates combine
            myDelegate=(MultiCast.strMultiCast)System.Delegate.Combine(Run,Walk);

        }
    }
}

31. Can a nested object be used in Serialization ?

Ans : Yes. If a class that is to be serialized contains references to objects of other classes, and if those classes
have been marked as serializable, then their objects are serialized too.

32. Difference between int and int32 ?

Ans : Both are same. System.Int32 is a .NET class. Int is an alias name for System.Int32.
33. Describe the difference between a Thread and a Process?

Ans : A Process is an instance of an running application. And a thread is the Execution stream of the Process. A
process                     can                     have                     multiple                    Thread.
When a process starts a specific memory area is allocated to it. When there is multiple thread in a process,
each thread gets a memory for storing the variables in it and plus they can access to the global variables
which is common for all the thread. Eg.A Microsoft Word is a Application. When you open a word file,an
instance of the Word starts and a process is allocated to this instance which has one thread.

34.       What       is     the      difference       between    an     EXE        and       a     DLL?
Ans      :     You     can    create     an     objects    of  Dll   but      not     of     the    EXE.
Dll is an In-Process Component whereas EXE is an OUt-Process Component.Exe is for single use whereas you
can                  use                 Dll               for             multiple                 use.
Exe can be started as standalone where dll cannot be.

35. What is strong-typing versus weak-typing? Which is preferred? Why? Ans : Strong typing implies
that the types of variables involved in operations are associated to the variable, checked at compile-time, and
require explicit conversion; weak typing implies that they are associated to the value, checked at run-time,
and are implicitly converted as required. (Which is preferred is a disputable point, but I personally prefer
strong typing because I like my errors to be found as soon as possible.)

36.    What      is    a    PID?     How      is    it   useful     when troubleshooting a    system?
PID is the process Id of the application in Windows. Whenever a process starts running in the Windows
environment, it is associated with an individual process Id or PID.

37. The PID (Process ID) a unique number for each item on the Process Tab, Image Name list. How
do you get the PID to appear? Ans : In Task Manger, select the View menu, then select columns and check
PID (Process Identifier).

In Linux, PID is used to debug a process explicitly. However we cannot do this in a windows environment.

Microsoft has launched a SDK called as Microsoft Operations Management (MOM). This uses the PID to find out
which dll‘s have been loaded by a process in the memory. This is essentially helpful in situations where the
Process which has a memory leak is to be traced to a erring dll. Personally I have never used a PID, our
Windows debugger does the things required to find out.

38.        What        is      the         GAC?          What        problem        does        it     solve?
Each computer where the common language runtime is installed has a machine-wide code cache called the
global assembly cache. The global assembly cache stores assemblies that are to be shared by several
applications on the computer. This area is typically the folder under windows or winnt in the machine.

All the assemblies that need to be shared across applications need to be done through the Global assembly
Cache only. However it is not necessary to install assemblies into the global assembly cache to make them
accessible to COM interop or unmanaged code.

There are several ways to deploy an assembly into the global assembly cache:
· Use an installer designed to work with the global assembly cache. This is the preferred option for installing
assemblies into the global assembly cache.
· Use a developer tool called the Global Assembly Cache tool (Gacutil.exe), provided by the .NET Framework
SDK.
· Use Windows Explorer to drag assemblies into the cache.

GAC solves the problem of DLL Hell and DLL versioning. Unlike earlier situations, GAC can hold two assemblies
of the same name but different version. This ensures that the applications which access a particular assembly
continue to access the same assembly even if another version of that assembly is installed on that machine.

39.     Describe     what     an    Interface     is    and    how     it’s   different    from      a    Class.
An interface is a structure of code which is similar to a class. An interface is a prototype for a class and is
useful from a logical design perspective. Interfaces provide a means to define the protocols for a class without
worrying    about     the   implementation     details.  The    syntax    for   creating  interfaces     follows:
interface Identifier
 {
 InterfaceBody
}

Identifier is the name of the interface and InterfaceBody refers to the abstract methods and static final
variables that make up the interface. Because it is assumed that all the methods in an interface are abstract, it
isn't necessary to use the abstract keyword

An interface is a description of some of the members available from a class. In practice, the syntax typically
looks similar to a class definition, except that there's no code defined for the methods — just their name, the
arguments passed and the type of the value returned.
So what good is it? None by itself. But you create an interface so that classes will implement it.

But what does it mean to implement an interface. The interface acts as a contract or promise. If a class
implements an interface, then it must have the properties and methods of the interface defined in the class.
This is enforced by the compiler.

Broadly the differentiators between classes and interfaces is as follows
• Interface should not have any implementation.
• Interface can not create any instance.
• Interface should provide high level abstraction from the implementation.
• Interface can have multiple inheritances.
• Default access level of the interface is public.

40. What is the difference between XML Web Services using ASMX and .NET Remoting using SOAP?

 ASP.NET Web services and .NET Remoting provide a full suite of design options for cross-process and cross-
plaform communication in distributed applications. In general, ASP.NET Web services provide the highest
levels of interoperability with full support for WSDL and SOAP over HTTP, while .NET Remoting is designed for
common language runtime type-system fidelity and supports additional data format and communication
channels. Hence if we looking cross-platform communication than web services is the choice coz for .NET
remoting .Net framework is requried which may or may not present for the other platform. Serialization and
Metadata
ASP.NET Web services rely on the System.Xml.Serialization.XmlSerializer class to marshal data to and from
SOAP messages at runtime. For metadata, they generate WSDL and XSD definitions that describe what their
messages contain. The reliance on pure WSDL and XSD makes ASP.NET Web services metadata portable; it
expresses data structures in a way that other Web service toolkits on different platforms and with different
programming models can understand. In some cases, this imposes constraints on the types you can expose
from a Web service—XmlSerializer will only marshal things that can be expressed in XSD. Specifically,
XmlSerializer will not marshal object graphs and it has limited support for container types.

.NET Remoting relies on the pluggable implementations of the IFormatter interface used by the
System.Runtime.Serialization engine to marshal data to and from messages. There are two standard
formatters,                 System.Runtime.Serialization.Formatters.Binary.BinaryFormatter               and
System.Runtime.Serialization.Formatters.Soap.SoapFormatter. The BinaryFormatter and SoapFormatter, as
the names suggest, marshal types in binary and SOAP format respectively. For metadata, .NET Remoting relies
on the common language runtime assemblies, which contain all the relevant information about the data types
they implement, and expose it via reflection. The reliance on the assemblies for metadata makes it easy to
preserve the full runtime type-system fidelity. As a result, when the .NET Remoting plumbing marshals data, it
includes all of a class's public and private members; handles object graphs correctly; and supports all
container types (e.g., System.Collections.Hashtable). However, the reliance on runtime metadata also limits
the reach of a .NET Remoting system—a client has to understand .NET constructs in order to communicate
with a .NET Remoting endpoint. In addition to pluggable formatters, the .NET Remoting layer supports
pluggable channels, which abstract away the details of how messages are sent. There are two standard
channels, one for raw TCP and one for HTTP. Messages can be sent over either channel independent of format.

Distributed      Application     Design:       ASP.NET      Web      Services    vs.    .NET       Remoting
ASP.NET Web services favor the XML Schema type system, and provide a simple programming model with
broad cross-platform reach. .NET Remoting favors the runtime type system, and provides a more complex
programming model with much more limited reach. This essential difference is the primary factor in
determining which technology to use. However, there are a wide range of other design factors, including
transport protocols, host processes, security, performance, state management, and support for transactions to
consider as well.
Security

Since ASP.NET Web services rely on HTTP, they integrate with the standard Internet security infrastructure.
ASP.NET leverages the security features available with IIS to provide strong support for standard HTTP
authentication schemes including Basic, Digest, digital certificates, and even Microsoft® .NET Passport. (You
can also use Windows Integrated authentication, but only for clients in a trusted domain.) One advantage of
using the available HTTP authentication schemes is that no code change is required in a Web service; IIS
performs authentication before the ASP.NET Web services are called. ASP.NET also provides support for .NET
Passport-based authentication and other custom authentication schemes. ASP.NET supports access control
based on target URLs, and by integrating with the .NET code access security (CAS) infrastructure. SSL can be
used to ensure private communication over the wire.

Although these standard transport-level techniques to secure Web services are quite effective, they only go so
far. In complex scenarios involving multiple Web services in different trust domains, you have to build custom
ad hoc solutions. Microsoft and others are working on a set of security specifications that build on the
extensibility of SOAP messages to offer message-level security capabilities. One of these is the XML Web
Services Security Language (WS-Security), which defines a framework for message-level credential transfer,
message integrity, and message confidentiality.

As noted in the previous section, the .NET Remoting plumbing does not secure cross-process invocations in the
general case. A .NET Remoting endpoint hosted in IIS with ASP.NET can leverage all the same security
features available to ASP.NET Web services, including support for secure communication over the wire using
SSL. If you are using the TCP channel or the HTTP channel hosted in processes other than aspnet_wp.exe, you
have to implement authentication, authorization and privacy mechanisms yourself.

One additional security concern is the ability to execute code from a semi-trusted environment without having
to change the default security policy. ASP.NET Web Services client proxies work in these environments, but
.NET Remoting proxies do not. In order to use a .NET Remoting proxy from a semi-trusted environment, you
need a special serialization permission that is not given to code loaded from your intranet or the Internet by
default. If you want to use a .NET Remoting client from within a semi-trusted environment, you have to alter
the default security policy for code loaded from those zones. In situations where you are connecting to
systems from clients running in a sandbox—like a downloaded Windows Forms application, for instance—
ASP.NET Web Services are a simpler choice because security policy changes are not required.

Conceptually, what is the difference between early-binding and late-binding?
Early binding – Binding at Compile Time
Late Binding – Binding at Run Time

Early binding implies that the class of the called object is known at compile-time; late-binding implies that the
class is not known until run-time, such as a call through an interface or via Reflection.

Early binding is the preferred method. It is the best performer because your application binds directly to the
address of the function being called and there is no extra overhead in doing a run-time lookup. In terms of
overall execution speed, it is at least twice as fast as late binding.

Early binding also provides type safety. When you have a reference set to the component's type library, Visual
Basic provides IntelliSense support to help you code each function correctly. Visual Basic also warns you if the
data type of a parameter or return value is incorrect, saving a lot of time when writing and debugging code.

Late binding is still useful in situations where the exact interface of an object is not known at design-time. If
your application seeks to talk with multiple unknown servers or needs to invoke functions by name (using the
Visual Basic 6.0 CallByName function for example) then you need to use late binding. Late binding is also
useful to work around compatibility problems between multiple versions of a component that has improperly
modified or adapted its interface between versions.
41. What is an Asssembly Qualified Name? Is it a filename? How is it different?

An assembly qualified name isn't the filename of the assembly; it's the internal name of the assembly
combined with the assembly version, culture, and public key, thus making it unique.

e.g. (""System.Xml.XmlDocument, System.Xml, Version=1.0.3300.0, Culture=neutral,
PublicKeyToken=b77a5c561934e089"")

42. How is a strongly-named assembly different from one that isn’t strongly-named?

Strong names are used to enable the stricter naming requirements associated with shared assemblies. These
strong names are created by a .NET utility – sn.exe

Strong names have three goals:
· Name uniqueness. Shared assemblies must have names that are globally unique.
· Prevent name spoofing. Developers don't want someone else releasing a subsequent version of one of your
assemblies and falsely claim it came from you, either by accident or intentionally.
· Provide identity on reference. When resolving a reference to an assembly, strong names are used to
guarantee the assembly that is loaded came from the expected publisher.

Strong names are implemented using standard public key cryptography. In general, the process works as
follows: The author of an assembly generates a key pair (or uses an existing one), signs the file containing the
manifest with the private key, and makes the public key available to callers. When references are made to the
assembly, the caller records the public key corresponding to the private key used to generate the strong
name.

Weak named assemblies are not suitable to be added in GAC and shared. It is essential for an assembly to be
strong named.

Strong naming prevents tampering and enables assemblies to be placed in the GAC alongside other assemblies
of the same name.

43. How does the generational garbage collector in the .NET CLR manage object lifetime? What is
non-deterministic                                                                                 finalization?
The hugely simplistic version is that every time it garbage-collects, it starts by assuming everything to be
garbage, then goes through and builds a list of everything reachable. Those become not-garbage, everything
else doesn't, and gets thrown away. What makes it generational is that every time an object goes through this
process and survives, it is noted as being a member of an older generation (up to 2, right now). When the
garbage-collector is trying to free memory, it starts with the lowest generation (0) and only works up to higher
ones if it can't free up enough space, on the grounds that shorter-lived objects are more likely to have been
freed than longer-lived ones.

Non-deterministic finalization implies that the destructor (if any) of an object will not necessarily be run (nor
its memory cleaned up, but that's a relatively minor issue) immediately upon its going out of scope. Instead, it
will wait until first the garbage collector gets around to finding it, and then the finalisation queue empties down
to it; and if the process ends before this happens, it may not be finalised at all. (Although the operating
system will usually clean up any process-external resources left open - note the usually there, especially as the
exceptions tend to hurt a lot.)

44.      What         is       the       difference        between          Finalize()        and       Dispose()?
Dispose() is called by the user of an object to indicate that he is finished with it, enabling that object to release
any unmanaged resources it holds. Finalize() is called by the run-time to allow an object which has not had
Dispose() called on it to do the same. However, Dispose() operates determinalistically, whereas there is no
guarantee that Finalize() will be called immediately when an object goes out of scope - or indeed at all, if the
program ends before that object is GCed - and as such Dispose() is generally preferred.

45. How is the using() pattern useful? What is IDisposable? How does it support deterministic
finalization?
The using() pattern is useful because it ensures that Dispose() will always be called when a disposable object
(defined as one that implements IDisposable, and thus the Dispose() method) goes out of scope, even if it
does so by an exception being thrown, and thus that resources are always released.
46.      What       does     this     useful     command        line    do?    tasklist    /m     "mscor*"
Lists all the applications and associated tasks/process currently running on the system with a module whose
name begins "mscor" loaded into them; which in nearly all cases means "all the .NET processes".

47.      What’s      wrong         with       a      line      like     this?     DateTime.Parse(myString);
Therez nothing wrong with this declaration.Converts the specified string representation of a date and time to
its DateTime equivalent.But If the string is not a valid DateTime,It throws an exception.

48.    What     are    PDBs?     Where       must     they    be     located    for   debugging        to     work?
A program database (PDB) files holds debugging and project state information that allows incremental linking
of debug configuration of your program.There are several different types of symbolic debugging information.
The default type for Microsoft compiler is the so-called PDB file. The compiler setting for creating this file is /Zi,
or /ZI for C/C++(which creates a PDB file with additional information that enables a feature called ""Edit and
Continue"") or a Visual Basic/C#/JScript .NET program with /debug.

A PDB file is a separate file, placed by default in the Debug project subdirectory, that has the same name as
the executable file with the extension .pdb. Note that the Visual C++ compiler by default creates an additional
PDB file called VC60.pdb for VisulaC++6.0 and VC70.PDB file for VisulaC++7.0. The compiler creates this file
during compilation of the source code, when the compiler isn't aware of the final name of the executable. The
linker can merge this temporary PDB file into the main one if you tell it to, but it won't do it by default. The
PDB file can be useful to display the detailed stack trace with source files and line numbers.

49.       What       is     FullTrust?       Do        GAC’ed       assemblies       have        FullTrust?
Before the .NET Framework existed, Windows had two levels of trust for downloaded code. This old model was
a binary trust model. You only had two choices: Full Trust, and No Trust. The code could either do anything
you           could        do,         or           it         wouldn't         run          at         all.

The permission sets in .NET include FullTrust, SkipVerification, Execution, Nothing, LocalIntranet, Internet and
Everything. Full Trust Grants unrestricted permissions to system resources. Fully trusted code run by a normal,
nonprivileged user cannot do administrative tasks, but can access any resources the user can access, and do
anything the user can do. From a security standpoint, you can think of fully trusted code as being similar to
native,        unmanaged             code,          like         a        traditional       ActiveX        control.
GAC assemblies are granted FullTrust. In v1.0 and 1.1, the fact that assemblies in the GAC seem to always get
a FullTrust grant is actually a side effect of the fact that the GAC lives on the local machine. If anyone were to
lock down the security policy by changing the grant set of the local machine to something less than FullTrust,
and if your assembly did not get extra permission from some other code group, it would no longer have
FullTrust even though it lives in the GAC.

50.        What        does      this       do?     gacutil       /l     |       find     /i    "Corillian"
The Global Assembly Cache tool allows you to view and manipulate the contents of the global assembly cache
and     download      cache.The     tool   comes    with    various    optional    params    to  do    that.
""/l"" option Lists the contents of the global assembly cache. If you specify the assemblyName parameter(/l
[assemblyName]), the tool lists only the assemblies matching that name.

51. What does this do .. sn -t foo.dll ?

Sn -t option displays the token for the public key stored in infile. The contents of infile must be previously
generated                                               using                                              -p.
Sn.exe computes the token using a hash function from the public key. To save space, the common language
runtime stores public key tokens in the manifest as part of a reference to another assembly when it records a
dependency to an assembly that has a strong name. The -tp option displays the public key in addition to the
token.

52. How do you generate a strong name?

.NET provides an utility called strong name tool. You can run this toolfrom the VS.NET command prompt to
generate a strong name with an option "-k" and providing the strong key file name. i.e. sn- -k < file-name >

What is the difference between a Debug and Release build? Is there a significant speed difference? Why or why
not?
The Debug build is the program compiled with full symbolic debug information and no optimization. The
Release build is the program compiled employing optimization and contains no symbolic debug information.
These settings can be changed as per need from Project Configuration properties. The release runs faster since
it does not have any debug symbols and is optimized.

53.            Explain      the      use     of     virtual,       sealed,      override,       and    abstract.
Abstract:       The      keyword        can      be      applied       for      a      class      or     method.
1.      Class:     If    we       use     abstract    keyword        for      a    class     it     makes    the
class      an     abstract      class,    which     means        it      cant     be     instantiated.    Though
it is not nessacary to make all the method within the abstract class to be virtual. ie, Abstract class can have
concrete                                                                                                 methods
2. Method: If we make a method as abstract, we dont need to provide implementation of the method in the
class but the derived class need to implement/override this method.

Sealed: It can be applied on a class and methods. It stops the type from further derivation i.e no one can
derive                                                                                                     class
from a sealed class,ie A sealed class cannot be inherited.A sealed class cannot be a abstract class.A compile
time    error   is    thrown    if   you    try   to    specify   sealed     class    as    a   base      class.
When an instance method declaration includes a sealed modifier, that method is said to be a sealed method. If
an instance method declaration includes the sealed modifier, it must also include the override modifier. Use of
the sealed modifier prevents a derived class from further overriding the method For Egs: sealed override
public void Sample() { Console.WriteLine("Sealed Method"); }



Virtual & Override: Virtual & Override keywords provides runtime polymorphism. A base class can make some
of its methods
as virtual which allows the derived class a chance to override the base class implementation by using override
keyword.

For e.g. class Shape
  {
  int a
  public virtual void Display()
  {
   Console.WriteLine("Shape");
  }
 }

class Rectangle:Shape
{
 public override void Display()
 {
  Console.WriteLine("Derived");
 }
}

54. Explain the importance and use of each, Version, Culture and PublicKeyToken for an assembly.
This three alongwith name of the assembly provide a strong name or fully qualified name to the assembly.
When a assebly is referenced with all three.

PublicKeyToken: Each assembly can have a public key embedded in its manifest that identifies the developer.
This ensures that once the assembly ships, no one can modify the code or other resources contained in the
assembly.

Culture:          Specifies          which           culture          the           assembly           supports

Version: The version number of the assembly.It is of the following form major.minor.build.revision.

Explain      the      differences     between       public,      protected,     private       and     internal.
These all are access modifier and they governs the access level. They can be applied to class, methods, fields.

Public: Allows class, methods, fields to be accessible from anywhere i.e. within and outside an assembly.

Private: When applied to field and method allows to be accessible within a class.
Protected: Similar to private but can be accessed by members of derived class also.

Internal: They are public within the assembly i.e. they can be accessed by anyone within an assembly but
outside assembly they are not visible.

55.     What       is    the      difference     between      typeof(foo)     and      myFoo.GetType()?
Typeof is operator which applied to a object returns System.Type object. Typeof cannot be overloaded white
GetType has lot of overloads.GetType is a method which also returns System.Type of an object. GetType is
used to get the runtime type of the object.

Example from MSDN showing Gettype used to retrive type at untime:-

public class MyBaseClass: Object {
}

public class MyDerivedClass: MyBaseClass {
}

public class Test {

    public static void Main() {
      MyBaseClass myBase = new MyBaseClass();
      MyDerivedClass myDerived = new MyDerivedClass();
      object o = myDerived;
      MyBaseClass b = myDerived;

        Console.WriteLine("mybase: Type is {0}", myBase.GetType());
        Console.WriteLine("myDerived: Type is {0}", myDerived.GetType());
        Console.WriteLine("object o = myDerived: Type is {0}", o.GetType());
        Console.WriteLine("MyBaseClass b = myDerived: Type is {0}", b.GetType());
    }
}



/*

This code produces the following output.

mybase: Type is MyBaseClass
myDerived: Type is MyDerivedClass
object o = myDerived: Type is MyDerivedClass
MyBaseClass b = myDerived: Type is MyDerivedClass

*/

56.         Can         "this"         be        used           within        a        static         method?
No 'This' cannot be used in a static method. As only static variables/methods can be used in a static method.

57. What is the purpose of XML Namespaces?

An XML Namespace is a collection of element types and attribute names. It consists of 2 parts
1)     The       first   part    is     the      URI      used     to    identify     the    namespace
2)    The       second    part     is    the     element      type    or    attribute     name   itself.
Together they form a unique name. The various purpose of XML Namespace are

1. Combine fragments from different documents without any naming conflicts. (See example below.)
2. Write reusable code modules that can be invoked for specific elements and attributes. Universally unique
names                                           guarantee                                               that
such     modules     are    invoked     only    for     the     correct    elements      and     attributes.
3. Define elements and attributes that can be reused in other schemas or instance documents without fear of
name                                               collisions.                                           For
example, you might use XHTML elements in a parts catalog to provide part descriptions. Or you might use the
nil                                                                                                attribute
defined in XML Schemas to indicate a missing value.

< Department >
   < Name >DVS1< /Name >
   < addr:Address xmlns:addr="http://www.tu-darmstadt.de/ito/addresses" >
     < addr:Street >Wilhelminenstr. 7< /addr:Street >
     < addr:City >Darmstadt< /addr:City >
     < addr:State >Hessen< /addr:State >
     < addr:Country >Germany< /addr:Country >
     < addr:PostalCode >D-64285< /addr:PostalCode >
   < /addr:Address >
   < serv:Server xmlns:serv="http://www.tu-darmstadt.de/ito/servers" >
     < serv:Name >OurWebServer< /serv:Name >
     < serv:Address >123.45.67.8< /serv:Address >
   < /serv:Server >
 < /Department >

58.        What        is       difference           between MetaData          and       Manifest       ?
Metadata and Manifest forms an integral part of an assembly( dll / exe ) in .net framework . Out of which
Metadata is a mandatory component , which as the name suggests gives the details about various components
of IL code viz : Methods , properties , fields , class etc.

Essentially Metadata maintains details in form of tables like Methods Metadata tables , Properties Metadata
tables , which maintains the list of given type and other details like access specifier , return type etc.

Now Manifest is a part of metadata only , fully called as ―manifest metadata tables‖ , it contains the details of
the references needed by the assembly of any other external assembly / type , it could be a custom assembly
or standard System namespace .

Now for an assembly that can independently exists and used in the .Net world both the things ( Metadata with
Manifest ) are mandatory , so that it can be fully described assembly and can be ported anywhere without any
system dependency . Essentially .Net framework can read all assembly related information from assembly
itself at runtime .

But for .Net modules , that can‘t be used independently , until they are being packaged as a part of an
assembly , they don‘t contain Manifest but their complete structure is defined by their respective metadata .

Ultimately . .Net modules use Manifest Metadata tables of parent assembly which contain them .



59. What is the use of Internal keyword?

Internal keyword is one of the access specifier available in .Net framework , that makes a type visible in a
given assembly , for e.g : a single dll can contain multiple modules , essentially a multi file assembly , but it
forms a single binary component , so any type with internal keyword will be visible throughout the assembly
and can be used in any of the modules .



60. What actually happes when you add a something to arraylistcollection ?

Following things will happen :

Arraylist is a dynamic array class in c# in System.Collections namespace derived from interfaces – ICollection ,
IList , ICloneable , IConvertible . It terms of in memory structure following is the implementation .
a. Check up the total space if there‘s any free space on the declared list .
b. If yes add the new item and increase count by 1 .
c. If No Copy the whole thing to a temporary Array of Last Max. Size .
d. Create new Array with size ( Last Array Size + Increase Value )
e. Copy back values from temp and reference this new array as original array .
f. Must doing Method updates too , need to check it up .

61. What is Boxing and unboxing? Does it occure automaatically or u need to write code to box and
unbox?

 Boxing – Process of converting a System.ValueType to Reference Type , Mostly base class System.Object type
and allocating it memory on Heap .Reverse is unboxing , but can only be done with prior boxed variables.

Boxing is always implicit but Unboxing needs to be explicitly done via casting , thus ensuring the value type
contained inside .

62. How Boxing and unboxing occures in memory?

Boxing converts value type to reference type , thus allocating memory on Heap . Unboxing converts already
boxed reference types to value types through explicit casting , thus allocating memory on stack .



63. Why only boxed types can be unboxed?

 Unboxing is the process of converting a Reference type variable to Value type and thus allocating memory on
the stack . It happens only to those Reference type variables that have been earlier created by Boxing of a
Value Type , therefore internally they contain a value type , which can be obtained through explicit casting .
For any other Reference type , they don‘t internally contain a Value type to Unboxed via explicit casting . This
is why only boxed types can be unboxed .

64. What is side-by-side execution? Can two application one using private assembly and other
using Shared assembly be stated as a side-by-side executables?

 Side-by-side execution is the ability to run multiple versions of an application or component on the same
computer. You can have multiple versions of the common language runtime, and multiple versions of
applications and components that use a version of the runtime, on the same computer at the same time. Since
versioning is only applied to shared assemblies, and not to private assemblies, two application one using
private assembly and one using shared assembly cannot be stated as side-by-side
executables.

65. Why string are called Immutable data Type ?

 The memory representation of string is an Array of Characters, So on re-assigning the new array of Char is
formed & the start address is changed . Thus keeping the Old string in Memory for Garbage Collector to be
disposed.

    66. What does assert() method do?
     In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if
    the condition is false. The program proceeds without any interruption if the condition is true.

67. What's the difference between the Debug class and Trace class? Documentation looks the same.
Use Debug class for debug builds, use Trace class for both debug and release builds.

68. Why are there five tracing levels in System.Diagnostics.TraceSwitcher? The tracing dumps can be
quite verbose. For applications that are constantly running you run the risk of overloading the machine and
the hard drive. Five levels range from None to Verbose, allowing you to fine-tune the tracing activities.

69. Where is the output of TextWriterTraceListener redirected?

To the Console or a text file depending on the parameter passed to the constructor.
70. How do assemblies find each other?

 By searching directory paths. There are several factors which can affect the path (such as the AppDomain
host, and application configuration files), but for private assemblies the search path is normally the
application's directory and its sub-directories. For shared assemblies, the search path is normally same as the
private assembly path plus the shared assembly cache.

71. How does assembly versioning work?

 Each assembly has a version number called the compatibility version. Also each reference to an assembly
(from another assembly) includes both the name and version of the referenced assembly.The version number
has four numeric parts (e.g. 5.5.2.33). Assemblies with either of the first two parts different are normally
viewed as incompatible. If the first two parts are the same, but the third is different, the assemblies are
deemed as 'maybe compatible'. If only the fourth part is different, the assemblies are deemed compatible.
However, this is just the default guideline - it is the version policy that decides to what extent these rules are
enforced. The version policy can be specified via the application configuration file.

72. What is garbage collection?

Garbage collection is a system whereby a run-time component takes responsibility for managing the lifetime of
objects and the heap memory that they occupy. This concept is not new to .NET - Java and many other
languages/runtimes have used garbage collection for some time.

73. Why doesn't the .NET runtime offer deterministic destruction?

Because of the garbage collection algorithm. The .NET garbage collector works by periodically running through
a list of all the objects that are currently being referenced by an application. All the objects that it doesn't find
during this search are ready to be destroyed and the memory reclaimed. The implication of this algorithm is
that the runtime doesn't get notified immediately when the final reference on an object goes away - it only
finds           out          during          the         next        sweep             of         the          heap.
Futhermore, this type of algorithm works best by performing the garbage collection sweep as rarely as
possible. Normally heap exhaustion is the trigger for a collection sweep.

74. Is the lack of deterministic destruction in .NET a problem?

It's certainly an issue that affects component design. If you have objects that maintain expensive or scarce
resources (e.g. database locks), you need to provide some way for the client to tell the object to release the
resource when it is done. Microsoft recommend that you provide a method called Dispose() for this purpose.
However, this causes problems for distributed objects - in a distributed system who calls the Dispose()
method? Some form of reference-counting or ownership-management mechanism is needed to handle
distributed objects - unfortunately the runtime offers no help with this.

75. What is serialization?

 Serialization is the process of converting an object into a stream of bytes. Deserialization is the opposite
process of creating an object from a stream of bytes. Serialization / Deserialization is mostly used to transport
objects (e.g. during remoting), or to persist
objects (e.g. to a file or database).

76. Does the .NET Framework have in-built support for serialization?

 There are two separate mechanisms provided by the .NET class library - XmlSerializer and
SoapFormatter/BinaryFormatter.    Microsoft   uses    XmlSerializer     for   Web    Services, and uses
SoapFormatter/BinaryFormatter for remoting. Both are available for use in your own code.

77. Can I customise the serialization process?

 Yes. XmlSerializer supports a range of attributes that can be used to configure serialization for a particular
class. For example, a field or property can be marked with the [XmlIgnore] attribute to exclude it from
serialization. Another example is the [XmlElement]
attribute, which can be used to specify the XML element name to be used for a particular property or field.
Serialization via SoapFormatter/BinaryFormatter can also be controlled to some extent by attributes. For
example, the [NonSerialized] attribute is the equivalent of XmlSerializer's [XmlIgnore] attribute. Ultimate
control of the serialization process can be acheived by implementing the the ISerializable interface on the class
whose instances are to be serialized.
78. Why is XmlSerializer so slow?

 There is a once-per-process-per-type overhead with XmlSerializer. So the first time you serialize or deserialize
an object of a given type in an application, there is a significant delay. This normally doesn't matter, but it may
mean, for example, that XmlSerializer is a poor choice for loading configuration settings during startup of a
GUI application.

79. Why do I get errors when I try to serialize a Hashtable?

 XmlSerializer will refuse to serialize instances of any class that implements IDictionary, e.g. Hashtable.
SoapFormatter and BinaryFormatter do not have this restriction.

80. What are attributes?

 There are at least two types of .NET attribute. The first type I will refer to as a metadata attribute - it allows
some data to be attached to a class or method. This data becomes part of the metadata for the class, and (like
other class metadata) can be accessed via reflection. The other type of attribute is a context attribute. Context
attributes use a similar syntax to metadata attributes but they are fundamentally different. Context attributes
provide an interception mechanism whereby instance activation and method calls can be
pre- and/or post-processed.

81. How does CAS work?

The CAS security policy revolves around two key concepts - code groups and permissions. Each .NET assembly
is a member of a particular code group, and each code group is granted the permissions specified in a named
permission                                                                                              set.
For example, using the default security policy, a control downloaded from a web site belongs to the 'Zone -
Internet' code group, which adheres to the permissions defined by the 'Internet' named permission set.
(Naturally the 'Internet' named permission set represents a very restrictive range of permissions.)

82. Who defines the CAS code groups?

 Microsoft defines some default ones, but you can modify these and even create your own. To see the code
groups defined on your system, run 'caspol -lg' from the command-line. On my system it looks like this:
Level = Machine
Code Groups:
1. All code: Nothing
  1.1. Zone - MyComputer: FullTrust
  1.1.1. Honor SkipVerification requests: SkipVerification
  1.2. Zone - Intranet: LocalIntranet
  1.3. Zone - Internet: Internet
  1.4. Zone - Untrusted: Nothing
  1.5. Zone - Trusted: Internet
  1.6. StrongName - 0024000004800000940000000602000000240000525341310004000003
000000CFCB3291AA715FE99D40D49040336F9056D7886FED46775BC7BB5430BA4444FEF8348EBD06
F962F39776AE4DC3B7B04A7FE6F49F25F740423EBF2C0B89698D8D08AC48D69CED0FC8F83B465E08
07AC11EC1DCC7D054E807A43336DDE408A5393A48556123272CEEEE72F1660B71927D38561AABF5C
AC1DF1734633C602F8F2D5:
Note the hierarchy of code groups - the top of the hierarchy is the most general ('All code'), which is then sub-
divided into several
groups, each of which in turn can be sub-divided. Also note that (somewhat counter-intuitively) a sub-group
can be associated with a more permissive permission set than its parent.

83. How do I define my own code group?

 Use caspol. For example, suppose you trust code from http://www.mydomain.com/ and you want it have full
access to your system, but you want to keep the default restrictions for all other internet sites. To achieve this,
you would add a new code group as a sub-group of the
'Zone - Internet' group, like this:
caspol -ag 1.3 -site http://www.mydomain.com/ FullTrust
Now if you run caspol -lg you will see that the new group has been added as group 1.3.1:

  1.3. Zone - Internet: Internet
    1.3.1. Site - http://www.mydomain.com/: FullTrust
Note that the numeric label (1.3.1) is just a caspol invention to make the code groups easy to manipulate from
the command-line. The underlying runtime never sees it.

84. How do I change the permission set for a code group?

 Use caspol. If you are the machine administrator, you can operate at the 'machine' level - which means not
only that the changes you make become the default for the machine, but also that users cannot change the
permissions to be more permissive. If you are a normal (non-admin) user you can still modify the permissions,
but only to make them more restrictive. For example, to allow intranet code to do what it likes you might do
this:                      caspol                       -cg                  1.2                    FullTrust
Note that because this is more permissive than the default policy (on a standard system), you should only do
this at the machine level - doing it at the user level will have no effect.

85. I can't be bothered with all this CAS stuff. Can I turn it off?

Yes, as long as you are an administrator. Just run: caspol -s off

86. Can I look at the IL for an assembly?

Yes. MS supply a tool called Ildasm which can be used to view the metadata and IL for an assembly.

87. Can source code be reverse-engineered from IL?

Yes, it is often relatively straightforward to regenerate high-level source (e.g. C#) from IL.

88. How can I stop my code being reverse-engineered from IL?

There is currently no simple way to stop code being reverse-engineered from IL. In future it is likely that IL
obfuscation tools will become available, either from MS or from third parties. These tools work by 'optimising'
the IL in such a way that reverse-engineering becomes much more difficult. Of course if you are writing web
services then reverse-engineering is not a problem as clients do not have access to your IL.

89. Is there built-in support for tracing/logging?

 Yes, in the System.Diagnostics namespace. There are two main classes that deal with tracing - Debug and
Trace. They both work in a similar way - the difference is that tracing from the Debug class only works in
builds that have the DEBUG symbol defined, whereas tracing from the Trace class only works in builds that
have the TRACE symbol defined. Typically this means that you should use System.Diagnostics.Trace.WriteLine
for tracing that you want to work in debug and release builds, and System.Diagnostics.Debug.WriteLine for
tracing that you want to work only in debug builds.

90. Can I redirect tracing to a file?

Yes. The Debug and Trace classes both have a Listeners property, which is a collection of sinks that receive the
tracing that you send via Debug.WriteLine and Trace.WriteLine respectively. By default the Listeners collection
contains a single sink, which is an instance of the DefaultTraceListener class. This sends output to the Win32
OutputDebugString() function and also the System.Diagnostics.Debugger.Log() method. This is useful when
debugging, but if you're trying to trace a problem at a customer site, redirecting the output to a file is more
appropriate. Fortunately, the TextWriterTraceListener class is provided for this purpose.

91. What are the contents of assembly?

In general, a static assembly can consist of four elements:
The assembly manifest, which contains assembly metadata.
Type metadata.
Microsoft intermediate language (MSIL) code that implements the types.
A set of resources.

92. What is GC (Garbage Collection) and how it works

 One of the good features of the CLR is Garbage Collection, which runs in the background collecting unused
object references, freeing us from having to ensure we always destroy them. In reality the time difference
between you releasing the object instance and it being garbage collected is likely to be very small, since the
GC is always running.
[The process of transitively tracing through all pointers to actively used objects in order to locate all objects
that can be referenced, and then arranging to reuse any heap memory that was not found during this trace.
The common language runtime garbage collector also compacts the memory that is in use to reduce the
working space needed for the heap.]

Heap:
A portion of memory reserved for a program to use for the temporary storage of data structures whose
existence or size cannot be determined until the program is running.

93. Differnce between Managed code and unmanaged code ? Managed Code: Code that runs under a
"contract of cooperation" with the common language runtime. Managed code must supply the metadata
necessary for the runtime to provide services such as memory management, cross-language integration, code
access security, and automatic lifetime control of objects. All code based on Microsoft intermediate language
(MSIL) executes as managed code.

Un-Managed Code:
Code that is created without regard for the conventions and requirements of the common language runtime.
Unmanaged code executes in the common language runtime environment with minimal services (for example,
no garbage collection, limited debugging, and so on).

94. What is MSIL, IL, CTS and, CLR ?
MSIL: (Microsoft intermediate language) When compiling to managed code, the compiler translates your
source code into Microsoft intermediate language (MSIL), which is a CPU-independent set of instructions that
can be efficiently converted to native code. MSIL includes instructions for loading, storing, initializing, and
calling methods on objects, as well as instructions for arithmetic and logical operations, control flow, direct
memory access, exception handling, and other operations. Before code can be executed, MSIL must be
converted to CPU-specific code, usually by a just-in-time (JIT) compiler. Because the common language
runtime supplies one or more JIT compilers for each computer architecture it supports, the same set of MSIL
can be JIT-compiled and executed on any supported architecture. When a compiler produces MSIL, it also
produces metadata. Metadata describes the types in your code, including the definition of
each type, the signatures of each type's members, the members that our code references, and other data that
the runtime uses at execution time. The MSIL and metadata are contained in a portable executable (PE) file
that is based on and extends the published Microsoft PE and Common Object File Format (COFF) used
historically for executable content. This file format, which accommodates

MSIL or native code as well as metadata, enables the operating system to recognize common language
runtime images. The presence of metadata in the file along with the MSIL enables your code to describe itself,
which means that there is no need for type libraries or Interface Definition Language (IDL). The runtime
locates and extracts the metadata from the file as needed during execution.

IL: (Intermediate Language)A language used as the output of a number of compilers and as the input to a
just-in-time (JIT) compiler. The common language runtime includes a JIT compiler for converting MSIL to
native code.

CTS: (Common Type System) The specification that determines how the common language runtime defines,
uses, and manages types

CLR: (Common Language Runtime) The engine at the core of managed code execution. The runtime supplies
managed code with services such as cross-language integration, code access security, object lifetime
management, and debugging and profiling support.

95.          What         is         Reference          type         and          value          type          ?
Reference Type: Reference types are allocated on the managed CLR heap, just like object types. A data type
that is stored as a reference to the value's location. The value of a reference type is the location of the
sequence of bits that represent the type's data. Reference types can be self-describing types, pointer types, or
interface types

Value Type: Value types are allocated on the stack just like primitive types in VBScript, VB6 and C/C++. Value
types are not instantiated using new go out of scope when the function they are defined within returns.
Value types in the CLR are defined as types that derive from system.valueType.

A data type that fully describes a value by specifying the sequence of bits that constitutes the value's
representation. Type information for a value type instance is not stored with the instance at run time, but it is
available in metadata. Value type instances can be treated as objects using boxing.
96. What is Boxing and unboxing ? Boxing: The conversion of a value type instance to an object, which
implies that the instance will carry full type information at run time and will be allocated in the heap. The
Microsoft intermediate language (MSIL) instruction set's box instruction converts a value type to an object by
making a copy of the value type and embedding it in a newly allocated object.
 Un-Boxing:
The conversion of an object instance to a value type.

97. What is JIT and how is works ? An acronym for "just-in-time," a phrase that describes an action that is
taken only when it becomes necessary, such as just-in-time compilation or just-in-time object activation

98. What is portable executable (PE) ? The file format used for executable programs and for files to be
linked together to form executable programs

99. What is strong name? A name that consists of an assembly's identity—its simple text name, version
number, and culture information (if provided)—strengthened by a public key and a digital signature generated
over the assembly. Because the assembly manifest contains file hashes for all the files that constitute the
assembly implementation, it is sufficient to generate the digital signature over just the one file in the assembly
that contains the assembly manifest. Assemblies with the same strong name are expected to be identical

100. What is global assembly cache? A machine-wide code cache that stores assemblies specifically
installed to be shared by many applications on the computer. Applications deployed in the global assembly
cache must have a strong name.

101.          What       is     difference      between      constants,       readonly       and,      static     ?
Constants: The value can‘t be changed
Read-only: The value will be initialized only once from the constructor of the class.
Static: Value can be initialized once.

102. What is difference between shared and public? An assembly that can be referenced by more than
one application. An assembly must be explicitly built to be shared by giving it a cryptographically strong name.

103. What is namespace used for loading assemblies at run time and name the methods?
System.Reflection

104. What are the types of authentication in .net? We have three types of authentication:
1. Form authentication
2. Windows authentication
3. Passport This has to be declared in web.config file.

105. What is the difference between a Struct and a Class ? The struct type is suitable for representing
lightweight objects such as Point, Rectangle, and Color. Although it is possible to represent a point as a class,
a struct is more efficient in some scenarios. For example, if you declare an array of 1000 Point objects, you will
allocate additional memory for referencing each object. In this case, the struct is less expensive. When you
create a struct object using the new operator, it gets created and the appropriate constructor is called. Unlike
classes, structs can be instantiated without using the new operator. If you do not use new, the fields will
remain unassigned and the object cannot be used until all of the fields are initialized. It is an error to declare a
default (parameterless) constructor for a struct. A default constructor is always provided to initialize the struct
members                         to                        their                  default                     values.
It      is      an       error       to       initialize        an    instance      field     in      a      struct.
There is no inheritance for structs as there is for classes. A struct cannot inherit from another struct or class,
and it cannot be the base of a class. Structs, however, inherit from the base class Object. A struct can
implement         interfaces,       and        it        does      that      exactly      as       classes       do.
A struct is a value type, while a class is a reference type.

106. How big is the datatype int in .NET?
32 bits.

107. How big is the char?
16 bits (Unicode).

108. How do you initiate a string without escaping each backslash?                 Put an @ sign in front of the
double-quoted string.

109. What's the access level of the visibility type internal?
Current application.
110. Explain encapsulation ? The implementation is hidden, the interface is exposed.

111. What data type should you use if you want an 8-bit value that's signed?
sbyte.

112. Speaking of Boolean data types, what's different between C# and C/C++?                            There's no
conversion between 0 and false, as well as any other number and true, like in C/C++.

113. Where are the value-type variables allocated in the computer RAM?
Stack.

114.      Where        do       the      reference-type        variables     go          in      the       RAM?
The references go on the stack, while the objects themselves go on the heap.

115. What is the difference between the value-type variables and reference-type variables in terms
of                                           garbage                                                 collection?
The value-type variables are not garbage-collected, they just fall off the stack when they fall out of scope, the
reference-type objects
are picked up by GC when their references go null.

116. How do you convert a string into an integer in .NET?
Int32.Parse(string)

117. How do you box a primitive data type variable?
Assign it to the object, pass an object.

118. Why do you need to box a primitive variable?
To pass it by reference.

119.     What's      the    difference     between       Java      and     .NET      garbage      collectors?
Sun left the implementation of a specific garbage collector up to the JRE developer, so their performance
varies widely, depending on whose JRE you're using. Microsoft standardized on their garbage collection.

120. How do you enforce garbage collection in .NET?
System.GC.Collect();

121. What's different about namespace declaration when comparing that to package declaration in
Java?
No semicolon.

122.         What's         the        difference       between          const       and        readonly?
You can initialize readonly variables to some runtime values. Let's say your program uses current date and
time as one of the values that won't change. This way you declare public readonly string DateT = new
DateTime().ToString().

123. What happens when you encounter a continue statement inside the for loop? The code for the
rest of the loop is ignored, the control is transferred back to the beginning of the loop.

124. What's the advantage of using System.Text.StringBuilder over System.String? StringBuilder is
more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each
time it's being operated on, a new instance is created.

125. Can you store multiple data types in System.Array?
No.

126. What's the difference between the System.Array.CopyTo() and System.Array.Clone()? The first
one performs a deep copy of the array, the second one is shallow.

127. How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.

128. What's the .NET datatype that allows the retrieval of data by a unique key?
HashTable.

129. What's class SortedList underneath?
A sorted HashTable.
130. Will finally block get executed if the exception had not occurred?
Yes.

131. Can multiple catch blocks be executed?
No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and
then whatever follows the finally block.

132.       Why        is    it    a     bad      idea      to     throw      your      own      exceptions?
Well, if at that point you know that an error has occurred, then why not write the proper code to handle that
error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies
some design flaws in the project.

133. What's a delegate?
A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.

134. What's a multicast delegate?
It's a delegate that points to and eventually fires off several methods.

135.       How's          the         DLL         Hell        problem            solved        in       .NET?
Assembly versioning allows the application to specify not only the library it needs to run (which was available
under Win32), but also the version of the assembly.

136. What are the ways to deploy an assembly?
 An MSI installer, a CAB archive, and XCOPY command.

137. What's a satellite assembly? When you write a multilingual or multi-cultural application in .NET, and
want to distribute the core application separately from the localized modules, the localized assemblies that
modify the core application are called satellite assemblies.

138. What namespaces are necessary to create a localized application?
System.Globalization, System.Resources.

140. What does assert() do? In debug compilation, assert takes in a Boolean condition as a parameter, and
shows the error dialog if the condition is false. The program proceeds without any interruption if the condition
is true.

141.    What's     the    difference   between       the     Debug      class     and     Trace     class?
Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release
builds.

142. Why are there five tracing levels in System.Diagnostics.TraceSwitcher? The tracing dumps can
be quite verbose and for some applications that are constantly running you run the risk of overloading the
machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing
activities.

143.      Where          is       the       output      of      TextWriterTraceListener                redirected?
To the Console or a text file depending on the parameter passed to the constructor.

144. What namespaces are necessary to create a localized application?
System.Globalization, System.Resources.

145.     What     are   three     test   cases     you    should    go    through  in   unit   testing?
Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper
handling), exception test cases (exceptions are thrown and caught properly).

146. Can you change the value of a variable while debugging                                 a   C#    application?
Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.

147. What's the implicit name of the parameter that gets passed into the class' set method?
Value, and it's datatype depends on whatever variable we're changing.

148. How do you inherit from a class in C#?
Place a colon and then the name of the base class. Notice that it's double colon in C++.
149. Does C# support multiple inheritance?
No, use interfaces instead.

150. When you inherit a protected class-level variable, who is it available to?
Derived Classes.

151. What's the top .NET class that everything is derived from?
System.Object.

152.              How's       method        overriding         different       from        overloading?
When overriding, you change the method behavior for a derived class. Overloading simply involves having a
method with the same name within the class.

153. What does the keyword virtual mean in the method definition?
The method can be over-ridden.

154. Can you declare the override method static while the original method is non-static? No, you
can't, the signature of the virtual method must remain the same, only the keyword virtual is changed to
keyword override.

155. Can you override private virtual methods? No, moreover, you cannot access private methods in
inherited classes, have to be protected in the base class to allow any sort of access.

156. Can you prevent your class from being inherited and becoming a base class for some other
classes?
Yes, that's what keyword sealed in the class definition is for. The developer trying to derive from your class will
get a message: cannot inherit from Sealed class WhateverBaseClassName. It's the same concept as final class
in Java.

157. Can you allow class to be inherited, but prevent the method from being over-ridden?
Yes, just leave the class public and make the method sealed.

158. Why can't you specify the accessibility modifier for methods inside the interface? They all
must be public. Therefore, to prevent you from getting the false impression that you have any freedom of
choice, you are not allowed to specify any accessibility, it's public by default.

159. Can you inherit multiple interfaces?
Yes, why not.

160.                 And         if        they        have       conflicting         method           names?
It's up to you to implement the method inside your own class, so implementation is left entirely up to you. This
might cause a problem on a higher-level scale if similarly named methods from different interfaces expect
different data, but as far as compiler cares you're okay.

161.      What's       the     difference       between        an     interface    and abstract    class?
In the interface all methods must be abstract, in the abstract class some methods can be concrete. In the
interface no accessibility modifiers are allowed, which is ok in abstract classes.

162. How can you overload a method?
Different parameter data types, different number of parameters, different order of parameters.

163. If a base class has a bunch of overloaded constructors, and an inherited class has another
bunch of overloaded constructors, can you enforce a call from an inherited constructor to an
arbitrary base constructor? Yes, just place a colon, and then keyword base (parameter list to invoke the
appropriate constructor) in the overloaded constructor definition inside the inherited class.

164. What's the difference between System.String and System.StringBuilder classes? System.String
is immutable, System.StringBuilder was designed with the purpose of having a mutable string where a variety
of operations can be performed.

165. Does C# support multiple-inheritance?
No, use interfaces instead.

166. When you inherit a protected class-level variable, who is it available to?
The derived class.
167.             Are             private            class-level              variables              inherited?
Yes, but they are not accessible. Although they are not visible or accessible via the class interface, they are
inherited.

168.          Describe          the         accessibility       modifier       "protected          internal".
It is available to derived classes and classes within the same Assembly (and naturally from the base class it's
declared in).

169. What's the top .NET class that everything is derived from?
System.Object.

170. What's the advantage of using System.Text.StringBuilder over System.String? StringBuilder is
more efficient in cases where there is a large amount of string manipulation. Strings are immutable, so each
time it's being operated on, a new instance is created.

171. Can you store multiple data types in System.Array?
No.

172. What's the .NET class that allows the retrieval of a data element using a unique key?
HashTable.

173. Will the finally block get executed if an exception has not occurred?
Yes.

174. What's an abstract class? A class that cannot be instantiated. An abstract class is a class that must
be inherited and have the methods overridden. An abstract class is essentially a blueprint for a class without
any implementation.

175. When do you absolutely have to declare a class as abstract?
 1.    When at least one of the methods in the class is abstract.
 2.    When the class itself is inherited from an abstract class, but not all base abstract methods have been
overridden.

176. What's an interface?
It's an abstract class with public abstract methods all of which must be implemented in the inherited classes.

177. Why can't you specify the accessibility modifier for methods inside the interface? They all must
be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice,
you are not allowed to specify any accessibility, it's public by default.

178.          What's       the     difference      between      an      interface      and    abstract class?
In an interface class, all methods must be abstract. In an abstract class some methods can be concrete. In
an interface class, no accessibility modifiers are allowed, which is ok in an abstract class.

179.         How      is   method      overriding      different   from       method   overloading?
When overriding a method, you change the behavior of the method for the derived class. Overloading a
method simply involves having another method with the same name within the class.

180. Can you declare an override method to be static if the original method is non-static? No. The
signature of the virtual method must remain the same, only the keyword virtual is changed to keyword
override.

181. Can you override private virtual methods?
No. Private methods are not accessible outside the class.

182. Can you write a class without specifying namespace? Which namespace does it belong to by
default?
Yes, you can, then the class belongs to global namespace which has no name. For commercial products,
naturally, you wouldn't want global namespace.



183. What is a formatter? A formatter is an object that is responsible for encoding and serializing data into
messages on one end, and deserializing and decoding messages into data on the other end.
184. Different b/w .NET & J2EE ?
Differences between J2EE and the .NET Platform

Vendor Neutrality

The .NET platform is not vendor neutral, it is tied to the Microsoft operating systems. But neither are any of
the                                             J2EE                                              implementations
Many companies buy into J2EE believing that it will give them vendor neutrality. And, in fact, this is a stated
goal                                 of                                 Sun's                              vision:
A wide variety of J2EE product configurations and implementations, all of which meet the requirements of this
specification, are possible. A portable J2EE application will function correctly when successfully deployed in any
of these products. (ref : Java 2 Platform Enterprise Edition Specification, v1.3, page 2-7 available at
http://java.sun.com/j2ee/)

Overall Maturity

Given that the .NET platform has a three year lead over J2EE, it should be no surprise to learn that the .NET
platform is far more mature than the J2EE platform. Whereas we have high volume highly reliable web sites
using .NET technologies (NASDAQ and Dell being among many examples)

Interoperability and Web Services

The .NET platform eCollaboration model is, as I have discussed at length, based on the UDDI and SOAP
standards. These standards are widely supported by more than 100 companies. Microsoft, along with IBM and
Ariba, are the leaders in this area. Sun is a member of the UDDI consortium and recognizes the importance of
the UDDI standards. In a recent press release, Sun's George Paolini, Vice President for the Java Community
Development, says:

"Sun has always worked to help establish and support open, standards-based technologies that facilitate the
growth of network-based applications, and we see UDDI as an important project to establish a registry
framework for business-to-business e-commerce

But while Sun publicly says it believes in the UDDI standards, in reality, Sun has done nothing whatsoever to
incorporate any of the UDDI standards into J2EE.

Scalability

Typical Comparision w.r.t Systems and their costs

J2EE

Company   System Total Sys.                               Cost
Bull      Escala T610 c/s                 16,785 $1,980,179
IBM       RS/6000 Enterprise Server F80 16,785 $2,026,681
Bull       Escala EPC810 c/s             33,375 $3,037,499
IBM        RS/6000 Enterprise Server M80 33,375 $3,097,055
Bull       Escala EPC2450                110,403 $9,563,263
IBM        IBM eServer pSeries 680 Model 7017-S85 110,403 $9,560,594



 .NET platform systems

Company System      Total Sys.                              Cost
Dell                PowerEdge 4400                    16,263 $273,487
Compaq              ProLiant ML-570-6/700-3P           20,207 $201,717
Dell                PowerEdge 6400               30,231 $334,626
IBM                 Netfinity 7600 c/s           32,377 $443,463
Compaq              ProLiant 8500-X550-64P       161,720 $3,534,272
Compaq              ProLiant 8500-X700-64P       179,658 $3,546,582
Compaq              ProLiant 8500-X550-96P       229,914 $5,305,571
Compaq               ProLiant 8500-X700-96P       262,244 $5,305,571
Compaq               ProLiant 8500-700-192P       505,303 $10,003,826




Framework Support

The .NET platform includes such an eCommerce framework called Commerce Server. At this point, there is no
equivalent vendor-neutral framework in the J2EE space. With J2EE, you should assume that you will be
building your new eCommerce solution from scratch

Moreover, no matter what [J2EE] vendor you choose, if you expect a component framework that will allow you
to quickly field complete e-business applications, you are in for a frustrating experience

Language

In the language arena, the choice is about as simple as it gets. J2EE supports Java, and only Java. It will not
support any other language in the foreseeable future. The .NET platform supports every language except Java
(although it does support a language that is syntactically and functionally equivalent to Java, C#). In fact,
given the importance of the .NET platform as a language independent vehicle, it is likely that any language
that comes out in the near future will include support for the .NET platform.

Some companies are under the impression that J2EE supports other languages. Although both IBM's
WebSphere and BEA's WebLogic support other languages, neither does it through their J2EE technology. There
are only two official ways in the J2EE platform to access other languages, one through the Java Native
Interface and the other through CORBA interoperability. Sun recommends the later approach. As Sun's
Distinguished Scientist and Java Architect Rick Cattell said in a recent interview.

Portability

The reason that operating system portability is a possibility with J2EE is not so much because of any inherent
portability of J2EE, as it is that most of the J2EE vendors support multiple operating systems. Therefore as
long as one sticks with a given J2EE vendor and a given database vendor, moving from one operating system
to another should be possible. This is probably the single most important benefit in favor of J2EE over the .NET
platform, which is limited to the Windows operating system. It is worth noting, however, that Microsoft has
submitted the specifications for C# and a subset of the .NET Framework (called the common language
infrastructure) to ECMA, the group that standardizes JavaScript.

J2EE offers an acceptable solution to ISVs when the product must be marketed to non-Windows customers,
particularly when the J2EE platform itself can be bundled with the ISV's product as an integrated offering.

If the primary customer base for the ISV is Windows customers, then the .NET platform should be chosen. It
will provide much better performance at a much lower cost.

Client device independence

The major difference being that with Java, it is the presentation tier programmer that determines the ultimate
HTML that will be delivered to the client, and with .NET, it is a Visual Studio.NET control.

This Java approach has three problems. First, it requires a lot of code on the presentation tier, since every
possible thin client system requires a different code path. Second, it is very difficult to test the code with every
possible thin client system. Third, it is very difficult to add new thin clients to an existing application, since to
do so involves searching through, and modifying a tremendous amount of presentation tier logic.

The .NET Framework approach is to write device independent code that interacts with visual controls. It is the
control, not the programmer, that is responsible for determining what HTML to deliver, based on the
capabilities of the client device.. In the .NET Framework model, one can forget that such a thing as HTML even
exists!
Conclusion

Sun's J2EE vision is based on a family of specifications that can be implemented by many vendors. It is open
in the sense that any company can license and implement the technology, but closed in the sense that it is
controlled by a single vendor, and a self contained architectural island with very limited ability to interact
outside of itself. One of J2EE's major disadvantages is that the choice of the platform dictates the use of a
single programming language, and a programming language that is not well suited for most businesses. One of
J2EE's major advantages is that most of the J2EE vendors do offer operating system portability.

Microsoft's .NET platform vision is a family of products rather than specifications, with specifications used
primarily to define points of interoperability. The major disadvantage of this approach is that if is limited to the
Windows platform, so applications written for the .NET platform can only be run on .NET platforms. Their are
several important advantages to the .NET platform:

* The cost of developing applications is much lower, since standard business languages can be used and
device independent presentation tier logic can be written.

* The cost of running applications is much lower, since commodity hardware platforms (at 1/5 the cost of their
Unix counterparts) can be used.

* The ability to scale up is much greater, with the proved ability to support at least ten times the number of
clients any J2EE platform has shown itself able to support.

* Interoperability is much stronger, with industry standard eCollaboration built into the platform.

185. What are the Main Features of .NET platform?

Features of .NET Platform are :-

Common Language Runtime Explains the features and benefits of the common language runtime, a run-time
environment that manages the execution of code and provides services that simplify the development process.

Assemblies
Defines the concept of assemblies, which are collections of types and resources that form logical units of
functionality. Assemblies are the fundamental units of deployment, version control, reuse, activation scoping,
and security permissions.

Application Domains
Explains how to use application domains to provide isolation between applications.

Runtime Hosts
Describes the runtime hosts supported by the .NET Framework, including ASP.NET, Internet Explorer, and shell
executables.

Common Type System
Identifies the types supported by the common language runtime.

Metadata and Self-Describing Components
Explains how the .NET Framework simplifies component interoperation by allowing compilers to emit additional
declarative information, or metadata, into all modules and assemblies.

Cross-Language Interoperability
Explains how managed objects created in different programming languages can interact with one another.

.NET Framework Security
Describes mechanisms for protecting resources and code from unauthorized code and unauthorized users.
.NET Framework Class Library
Introduces the library of types provided by the .NET Framework, which expedites and optimizes the
development process and gives you access to system functionality.

186. What is the use of JIT ? JIT (Just - In - Time) is a compiler which converts MSIL code to Native Code
(ie.. CPU-specific code that runs on the same computer architecture).

Because the common language runtime supplies a JIT compiler for each supported CPU architecture,
developers can write a set of MSIL that can be JIT-compiled and run on computers with different architectures.
However, your managed code will run only on a specific operating system if it calls platform-specific native
APIs, or a platform-specific class library.

JIT compilation takes into account the fact that some code might never get called during execution. Rather
than using time and memory to convert all the MSIL in a portable executable (PE) file to native code, it
converts the MSIL as needed during execution and stores the resulting native code so that it is accessible for
subsequent calls. The loader creates and attaches a stub to each of a type's methods when the type is loaded.
On the initial call to the method, the stub passes control to the JIT compiler, which converts the MSIL for that
method into native code and modifies the stub to direct execution to the location of the native code.
Subsequent calls of the JIT-compiled method proceed directly to the native code that was previously
generated, reducing the time it takes to JIT-compile and run the code.

187. What meant of assembly & global assembly cache (gac) & Meta data. Assembly :-- An assembly
is the primary building block of a .NET based application. It is a collection of functionality that is built,
versioned, and deployed as a single implementation unit (as one or more files). All managed types and
resources are marked either as accessible only within their implementation unit, or as accessible by code
outside that unit. It overcomes the problem of 'dll Hell'.The .NET Framework uses assemblies as the
fundamental unit for several purposes:


         Security
         Type Identity
         Reference Scope
        Versioning
         Deployment

Global Assembly Cache :-- Assemblies can be shared among multiple applications on the machine by
registering them in global Assembly cache(GAC). GAC is a machine wide a local cache of assemblies
maintained by the .NET Framework. We can register the assembly to global assembly cache by using gacutil
command.
We can Navigate to the GAC directory, C:\winnt\Assembly in explore. In the tools menu select the cache
properties; in the windows displayed you can set the memory limit in MB used by the GAC
MetaData :--Assemblies have Manifests. This Manifest contains Metadata information of the Module/Assembly
as well as it contains detailed Metadata of other assemblies/modules references (exported). It's the Assembly
Manifest which differentiates between an Assembly and a Module.

188.       What        are     the  mobile       devices      supported        by     .net      platform
The Microsoft .NET Compact Framework is designed to run on mobile devices such as mobile phones, Personal
Digital Assistants (PDAs), and embedded devices. The easiest way to develop and test a Smart Device
Application is to use an emulator.

These devices are divided into two main divisions:
1) Those that are directly supported by .NET (Pocket PCs, i-Mode phones, and WAP devices)
2) Those that are not (Palm OS and J2ME-powered devices).

189.        What         is      GUID        ,       why         we       use       it       and         where?
GUID :-- GUID is Short form of Globally Unique Identifier, a unique 128-bit number that is produced by the
Windows OS or by some Windows applications to identify a particular component, application, file, database
entry, and/or user. For instance, a Web site may generate a GUID and assign it to a user's browser to record
and track the session. A GUID is also used in a Windows registry to identify COM DLLs. Knowing where to look
in the registry and having the correct GUID yields a lot information about a COM object (i.e., information in the
type library, its physical location, etc.). Windows also identifies user accounts by a username
(computer/domain and username) and assigns it a GUID. Some database administrators even will use GUIDs
as primary key values in databases.

GUIDs can be created in a number of ways, but usually they are a combination of a few unique settings based
on specific point in time (e.g., an IP address, network MAC address, clock date/time, etc.).

190. Describe the difference between inline and code behind - which is best in a loosely coupled
solution ASP.NET supports two modes of page development: Page logic code that is written inside
runat="server"> blocks within an .aspx file and dynamically compiled the first time the page is requested on
the server. Page logic code that is written within an external class that is compiled prior to deployment on a
server and linked ""behind"" the .aspx file at run time.

191. Whats MSIL, and why should my developers need an appreciation of it if at all? When compiling
the source code to managed code, the compiler translates the source into Microsoft intermediate language
(MSIL). This is a CPU-independent set of instructions that can efficiently be converted to native code. Microsoft
intermediate language (MSIL) is a translation used as the output of a number of compilers. It is the input to a
just-in-time (JIT) compiler. The Common Language Runtime includes a JIT compiler for the conversion of MSIL
to native code.

Before Microsoft Intermediate Language (MSIL) can be executed it, must be converted by the .NET Framework
just-in-time (JIT) compiler to native code. This is CPU-specific code that runs on the same computer
architecture as the JIT compiler. Rather than using time and memory to convert all of the MSIL in a portable
executable (PE) file to native code. It converts the MSIL as needed whilst executing, then caches the resulting
native code so its accessible for any subsequent calls.

192. How many .NET languages can a single .NET DLL contain?
One

193. What type of code (server or client) is found in a Code-Behind class?
Server

194. Whats an assembly? Assemblies are the building blocks of .NET Framework applications; they form
the fundamental unit of deployment, version control, reuse, activation scoping, and security permissions. An
assembly is a collection of types and resources that are built to work together and form a logical unit of
functionality. An assembly provides the common language runtime with the information it needs to be aware
of type implementations. To the runtime, a type does not exist outside the context of an assembly.

195. How many classes can a single .NET DLL contain?
Unlimited.

196. What is the difference between string and String ?
No difference

197. What is manifest?
It is the metadata that describes the assemblies.

198. What is metadata? Metadata is machine-readable information about a resource, or ""data about data.""
Such information might include details on content, format, size, or other characteristics of a data
source. In .NET, metadata includes type definitions, version information, external assembly references, and
other standardized information.

199. What are the types of assemblies?
There are four types of assemblies in .NET:

Static assemblies
These are the .NET PE files that you create at compile time.

Dynamic assemblies These are PE-formatted, in-memory assemblies that you dynamically create at runtime
using the classes in the System.Reflection.Emit namespace.
Private assemblies These are static assemblies used by a specific application.

Public or shared assemblies These are static assemblies that must have a unique shared name and can be
used by any application.

An application uses a private assembly by referring to the assembly using a static path or through an XML-
based application configuration file. While the CLR doesn't enforce versioning policies-checking whether the
correct       version      is     used-for      private     assemblies,       it      ensures       that     an
application uses the correct shared assemblies with which the application was built. Thus, an application uses a
specific shared assembly by referring to the specific shared assembly, and the CLR ensures that the correct
version is loaded at runtime.

In .NET, an assembly is the smallest unit to which you can associate a version number;

200. What are delegates?where are they used ? A delegate defines a reference type that can be used to
encapsulate a method with a specific signature. A delegate instance encapsulates a static or an instance
method. Delegates are roughly similar to function pointers in C++; however, delegates are type-safe and
secure.

201. When do you use virutal keyword?. When we need to override a method of the base class in the sub
class, then we give the virtual keyword in the base class method. This makes the method in the base class to
be overridable. Methods, properties, and indexers can be virtual, which means that their implementation can
be overridden in derived classes.

202. What are class access modifiers ? Access modifiers are keywords used to specify the declared
accessibility of a member or a type. This section introduces the four access modifiers:
· Public - Access is not restricted.
· Protected - Access is limited to the containing class or types derived from the containing class.
· Internal - Access is limited to the current assembly.
· Protected inertnal - Access is limited to the current assembly or types derived · from the containing class.
· Private - Access is limited to the containing type.

203. What Is Boxing And Unboxing?
Boxing :- Boxing is an implicit conversion of a value type to the type object type

Eg:-
Consider the following declaration of a value-type variable:
int i = 123;
object o = (object) i;
Boxing Conversion

UnBoxing :- Unboxing is an explicit conversion from the type object to a value type
Eg:
int i = 123;      // A value type
object box = i;    // Boxing
int j = (int)box;  // Unboxing

204. What is Value type and refernce type in .Net?.
Value Type : A variable of a value type always contains a value of that type. The assignment to a variable of a
value type creates a copy of the assigned value, while the assignment to a variable of a reference type creates
a copy of the reference but not of the referenced object.

The value types consist of two main categories:
* Stuct Type
* Enumeration Type

Reference Type :Variables of reference types, referred to as objects, store references to the actual data. This
section introduces the following keywords used to declare reference types:
* Class
* Interface
* Delegate
This section also introduces the following built-in reference types:
* object
* string

205.       What       is     the      difference      between        structures      and       enumeration?.
Unlike classes, structs are value types and do not require heap allocation. A variable of a struct type directly
contains the data of the struct, whereas a variable of a class type contains a reference to the data. They are
derived from System.ValueType class.

Enum->An enum type is a distinct type that declares a set of named constants.They are strongly typed
constants. They are unique types that allow to declare symbolic names to integral values. Enums are value
types, which means they contain their own value, can't inherit or be inherited from and assignment copies the
value of one enum to another.

public enum Grade
{
  A,
  B,
  C
}



206. What is namespaces?. Namespace is a logical naming scheme for group related types.Some class
types that logically belong together they can be put into a common namespace. They prevent namespace
collisions and they provide scoping. They are imported as "using" in C# or "Imports" in Visual Basic. It seems
as if these directives specify a particular assembly, but they don't. A namespace can span multiple assemblies,
and an assembly can define multiple namespaces. When the compiler needs the definition for a class type, it
tracks through each of the different imported namespaces to the type name and searches each referenced
assembly                         until                      it                    is                     found.
Namespaces can be nested. This is very similar to packages in Java as far as scoping is concerned.



207. How do you create shared assemblies?.
Just look through the definition of Assemblies..
  * An Assembly is a logical unit of code
  * Assembly physically exist as DLLs or EXEs
  * One assembly can contain one or more files
  * The constituent files can include any file types like image files, text files etc. along with DLLs or EXEs
  * When you compile your source code by default the exe/dll generated is actually an assembly
  * Unless your code is bundled as assembly it can not be used in any other application
  * When you talk about version of a component you are actually talking about version of the assembly to
which the component belongs.
  * Every assembly file contains information about itself. This information is called as Assembly Manifest.

Following steps are involved in creating shared assemblies :

  *   Create your DLL/EXE source code
  *   Generate unique assembly name using SN utility
  *   Sign your DLL/EXE with the private key by modifying AssemblyInfo file
  *   Compile your DLL/EXE
  *   Place the resultant DLL/EXE in global assembly cache using AL utility



208. What is global assembly cache?

Each computer where the common language runtime is installed has a machine-wide code cache called the
global assembly cache. The global assembly cache stores assemblies specifically designated to be shared by
several applications on the computer. There are several ways to deploy an assembly into the global assembly
cache: · Use an installer designed to work with the global assembly cache. This is the preferred option for
installing assemblies into the global assembly cache. Use a developer tool called the Global Assembly Cache
tool         (Gacutil.exe),        provided       by        the         .NET         Framework         SDK.
· Use Windows Explorer to drag assemblies into the cache.
209. What is MSIL?.

 When compiling to managed code, the compiler translates your source code into Microsoft intermediate
language (MSIL), which is a CPU-independent set of instructions that can be efficiently converted to native
code. MSIL includes instructions for loading, storing, initializing, and calling methods on objects, as well as
instructions for arithmetic and logical operations, control flow, direct memory access, exception handling, and
other operations. Before code can be run, MSIL must be converted to CPU-specific code, usually by a just-in-
time (JIT) compiler. Because the common language runtime supplies one or more JIT compilers for each
computer architecture it supports, the same set of MSIL can be JIT-compiled and run on any supported
architecture.
When a compiler produces MSIL, it also produces metadata. Metadata describes the types in your code,
including the definition of each type, the signatures of each type's members, the members that your code
references, and other data that the runtime uses at execution time. The MSIL and metadata are contained in a
portable executable (PE) file that is based on and extends the published Microsoft PE and common object file
format (COFF) used historically for executable content. This file format, which accommodates MSIL or native
code as well as metadata, enables the operating system to recognize common language runtime images. The
presence of metadata in the file along with the MSIL enables your code to describe itself, which means that
there is no need for type libraries or Interface Definition Language (IDL). The runtime locates and extracts the
metadata from the file as needed during execution.

210.           What        is    Jit      compilers?.how        many        are    available      in    clr?
Just-In-Time compiler- it converts the language that you write in .Net into machine language that a computer
can understand. there are tqo types of JITs one is memory optimized & other is performace optimized.

211.       What        is      tracing?Where        it     used.Explain         few      methods        available
Tracing refers to collecting information about the application while it is running. You use tracing information to
troubleshoot                                             an                                            application.
Tracing allows us to observe and correct programming errors. Tracing enables you to record information in
various log files about the errors that might occur at run time. You can analyze these log files to find the cause
of the errors.

In .NET we have objects called Trace Listeners. A listener is an object that receives the trace output and
outputs it somewhere; that somewhere could be a window in your development environment, a file on your
hard drive, a Windows Event log, a SQL Server or Oracle database, or any other customized data store.

The System.Diagnostics namespace provides the interfaces, classes, enumerations and structures that are
used for tracing The System.Diagnostics namespace provides two classes named Trace and Debug that are
used for writing errors and application execution information in logs.

All Trace Listeners have the following functions. Functionality of these functions is same except that the target
media for the tracing output is determined by the Trace Listener.

Method Name Result Fail Outputs the specified text with the Call Stack.
Write Outputs the specified text.
WriteLine Outputs the specified text and a carriage return.
Flush Flushes the output buffer to the target media.
Close Closes the output stream in order to not receive the tracing/debugging output.
                                C# AND VB.NET QUESTIONS



01. Explain the differences between Server-side and Client-side code? Server side code executes on
the server.For this to occur page has to be submitted or posted back.Events fired by the controls are executed
on the server.Client side code executes in the browser of the client without submitting the page. e.g. In
ASP.NET for webcontrols like asp:button the click event of the button is executed on the server hence the
event handler for the same in a part of the code-behind (server-side code). Along the server-side code events
one can also attach client side events which are executed in the clients browser i.e. javascript events.

02. How does VB.NET/C# achieve polymorphism? Polymorphism is also achieved through interfaces.
Like abstract classes, interfaces also describe the methods that a class needs to implement. The difference
between abstract classes and interfaces is that abstract classes always act as a base class of the related
classes in the class hierarchy. For example, consider a hierarchy-car and truck classes derived from four-
wheeler class; the classes two-wheeler and four-wheeler derived from an abstract class vehicle. So, the class
'vehicle' is the base class in the class hierarchy. On the other hand dissimilar classes can implement one
interface. For example, there is an interface that compares two objects. This interface can be implemented by
the classes like box, person and string, which are unrelated to each other.

C# allows multiple interface inheritance. It means that a class can implement more than one interface. The
methods declared in an interface are implicitly abstract. If a class implements an interface, it becomes
mandatory for the class to override all the methods declared in the interface, otherwise the derived class
would become abstract.

Can you explain what inheritance is and an example of when you might use it? The savingaccount class has
two data members-accno that stores account number, and trans that keeps track of the number of
transactions. We can create an object of savingaccount class as shown below.

          savingaccount       s   =      new      savingaccount      (   "Amar",      5600.00f      )      ;
From the constructor of savingaccount class we have called the two-argument constructor of the account class
using the base keyword and passed the name and balance to this constructor using which the data member's
name and balance are initialised.

We can write our own definition of a method that already exists in a base class. This is called method
overriding. We have overridden the deposit( ) and withdraw( ) methods in the savingaccount class so that we
can make sure that each account maintains a minimum balance of Rs. 500 and the total number of
transactions do not exceed 10. From these methods we have called the base class's methods to update the
balance using the base keyword. We have also overridden the display( ) method to display additional
information, i.e. account number.

Working of currentaccount class is more or less similar to that of savingaccount class. Using the derived
class's object, if we call a method that is not overridden in the derived class, the base class method gets
executed. Using derived class's object we can call base class's methods, but the reverse is not allowed.

Unlike C++, C# does not support multiple inheritance. So, in C# every class has exactly one base class. Now,
suppose we declare reference to the base class and store in it the address of instance of derived class as
shown below.

     account a1 = new savingaccount ( "Amar", 5600.00f ) ;
  account a2 = new currentaccount ( "MyCompany Pvt. Ltd.", 126000.00f) ;



Such a situation arises when we have to decide at run-time a method of which class in a class hierarchy should
get called. Using a1 and a2, suppose we call the method display( ), ideally the method of derived class should
get called. But it is the method of base class that gets called. This is because the compiler considers the type
of reference (account in this case) and resolves the method call. So, to call the proper method we must make
a small change in our program. We must use the virtual keyword while defining the methods in base class as
shown below.
      public virtual void display( ) { }
We must declare the methods as virtual if they are going to be overridden in derived class. To override a
virtual method in derived classes we must use the override keyword as given below.

      public override void display( ) { }
Now it is ensured that when we call the methods using upcasted reference, it is the derived class's method
that would get called. Actually, when we declare a virtual method, while calling it, the compiler considers the
contents of the reference rather than its type.

If we don't want to override base class's virtual method, we can declare it with new modifier in derived class.
The new modifier indicates that the method is new to this class and is not an override of a base class method.

03.        How         would        you        implement           inheritance        using       VB.NET/C#?
When we set out to implement a class using inheritance, we must first start with an existing class from which
we will derive our new subclass. This existing class, or base class, may be part of the .NET system class library
framework, it may be part of some other application or .NET assembly, or we may create it as part of our
existing application. Once we have a base class, we can then implement one or more subclasses based on that
base class. Each of our subclasses will automatically have all of the methods, properties, and events of that
base class ? including the implementation behind each method, property, and event. Our subclass can add new
methods, properties, and events of its own - extending the original interface with new functionality.
Additionally, a subclass can replace the methods and properties of the base class with its own new
implementation - effectively overriding the original behavior and replacing it with new behaviors. Essentially
inheritance is a way of merging functionality from an existing class into our new subclass. Inheritance also
defines rules for how these methods, properties, and events can be merged. In VB.NET we can use
implements keyword for inheritance, while in C# we can use the sign ( :: ) between subclass and baseclass.

04. How is a property designated as read-only?
In VB.NET:

Private mPropertyName as DataType
Public ReadOnly Property PropertyName() As DataType
   Get Return mPropertyName
   End Get
End Property

In C#

Private DataType mPropertyName;
public returntype PropertyName
{
    get{
                 //property implementation goes here
                 return mPropertyName;
         }
         // Do not write the set implementation
}



05. What is hiding in CSharp ?

Hiding is also called as Shadowing. This is the concept of Overriding the methods. It is a concept used in the
Object Oriented Programming.

E.g.
 public class ClassA {
 public virtual void MethodA() {
  Trace.WriteLine("ClassA Method");
 }
}
public class ClassB : ClassA {
 public new void MethodA() {
  Trace.WriteLine("SubClass ClassB Method");
 }
}

public class TopLevel {
 static void Main(string[] args) {
  TextWriter tw = Console.Out;
  Trace.Listeners.Add(new TextWriterTraceListener(tw));

 ClassA obj = new ClassB();
 obj.MethodA(); // Outputs ―Class A Method"

  ClassB obj1 = new ClassB();
  obj.MethodA(); // Outputs ―SubClass ClassB Method‖
 }
}

06. What is the difference between an XML "Fragment" and an XML "Document." An XML fragment is
an XML document with no single top-level root element. To put it simple it is a part (fragment) of a well-
formed xml document. (node) Where as a well-formed xml document must have only one root element.

07.       What       does       it    meant       to    say       “the     canonical”     form      of     XML?
"The purpose of Canonical XML is to define a standard format for an XML document. Canonical XML is a very
strict    XML     syntax,     which    lets   documents      in    canonical   XML    be   compared      directly.
Using this strict syntax makes it easier to see whether two XML documents are the same. For example, a
section of text in one document might read Black & White, whereas the same section of text might read Black
& White in another document, and even in another. If you compare those three documents byte by byte,
they'll be different. But if you write them all in canonical XML, which specifies every aspect of the syntax you
can use, these three documents would all have the same version of this text (which would be Black & White)
and could be compared without problem. This Comparison is especially critical when xml documents are
digitally signed. The digital signal may be interpreted in different way and the document may be rejected.



08. Why is the XML InfoSet specification different from the Xml DOM? What does the InfoSet
attempt to solve? "The XML Information Set (Infoset) defines a data model for XML. The Infoset describes
the abstract representation of an XML Document. Infoset is the generalized representation of the XML
Document, which is primarily meant to act as a set of definitions used by XML technologies to formally
describe      what       parts     of     an        XML        document        they       operate       upon.
The Document Object Model (DOM) is one technology for representing an XML Document in memory and to
programmatically read, modify and manipulate a xml document. Infoset helps defining generalized standards
on how to use XML that is not dependent or tied to a particular XML specification or API. The Infoset tells us
what part of XML Document should be considered as significant information.

09. Contrast DTDs versus XSDs. What are their similarities and differences? Which is preferred and
why? Document Type Definition (DTD) describes a model or set of rules for an XML document. XML Schema
Definition (XSD) also describes the structure of an XML document but XSDs are much more powerful. The
disadvantage with the Document Type Definition is it doesn‘t support data types beyond the basic 10 primitive
types. It cannot properly define the type of data contained by the tag. An Xml Schema provides an Object
Oriented approach to defining the format of an xml document. The Xml schema support most basic
programming types like integer, byte, string, float etc., We can also define complex types of our own which
can be used to define a xml document. Xml Schemas are always preferred over DTDs as a document can be
more precisely defined using the XML Schemas because of its rich support for data representation.

10. Speaking of Boolean data types, what's different between C# and C/C++?
There's no conversion between 0 and false, as well as any other number and true, like in C/C++.

11. How do you convert a string into an integer in .NET?
Int32.Parse(string)
12.    Can      you      declare      a       C++       type     destructor      in    C#    like    ~MyClass()?
Yes, but what's the point, since it will call Finalize(), and Finalize() has no guarantees when the memory will be
cleaned up, plus, it introduces additional load on the garbage collector.

13. What's different about namespace declaration when comparing that to package declaration in
Java?
No semicolon.

14. What's the difference between const and readonly?

 The readonly keyword is different from the const keyword. A const field can only be initialized at the
declaration of the field. A readonly field can be initialized either at the declaration or in a constructor.
Therefore, readonly fields can have different values depending on the constructor used. Also, while a const
field is a compile-time constant, the readonly field can be used for runtime constants as in the following
example:
public static readonly uint l1 = (uint) DateTime.Now.Ticks;

15. What does \a character do?
On most systems, produces a rather annoying beep.

16. Can you create enumerated data types in C#?
Yes.

17. What's different about switch statements in C#?
No fall-throughs allowed.

18. What happens when you encounter a continue statement inside the for loop?
The code for the rest of the loop is ignored, the control is transferred back to the beginning of the loop.

19. How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.

20. Will finally block get executed if the exception had not occurred?
Yes.

21. What's the C# equivalent of C++ catch (…), which was a catch-all statement for any possible
exception?
A catch block that catches the exception of type System.Exception. You can also omit the parameter data type
in this case and just write catch {}.

22. Can multiple catch blocks be executed?
No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and
then whatever follows the finally block.

23. Why is it a bad idea to throw your own exceptions?
Well, if at that point you know that an error has occurred, then why not write the proper code to handle that
error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies
some design flaws in the project.

24. What's the difference between // comments, /* */ comments and /// comments?
Single-line, multi-line and XML documentation comments.

25. How do you generate documentation from the C# file commented properly with a command-
line compiler?
Compile it with a /doc switch.

26. Can you change the value of a variable while debugging a C# application?
Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.
27. What's the implicit name of the parameter that gets passed into the class' set method?
Value, and it's datatype depends on whatever variable we're changing.

28. How do you inherit from a class in C#?
Place a colon and then the name of the base class. Notice that it's double colon in C++.

29. Does C# support multiple inheritance?
No, use interfaces instead.

30. So how do you retrieve the customized properties of a .NET application from XML .config file?
Can                     you                    automate                       this               process?
Initialize an instance of AppSettingsReader class. Call the GetValue method of AppSettingsReader class,
passing in the name of the property and the type expected. Assign the result to the appropriate variable. In
Visual Studio yes, use Dynamic Properties for automatic .config creation, storage and retrieval.

31. Why is it not a good idea to insert code into InitializeComponent method when working with
Visual                                                                                                 Studio?
The designer will likely through it away, most of the code inside InitializeComponent is auto-generated.

32. Where do you add an event handler?
It's the Attributesproperty, the Add function inside that property.
e.g. btnSubmit.Attributes.Add(""onMouseOver"",""someClientCode();"")

33. What are jagged array?

First      lets    us        answer       the       question     that       what      an      array         is?
The dictionary meaning of array is an orderly arrangement or sequential arrangement of elements.

In                              computer                            science                             term:
An array is a data structure that contains a number of variables, which are accessed through computed
indices. The variables contained in an array, also called the elements of the array, are all of the same type,
and this type is called the element type of the array.

An array has a rank that determines the number of indices associated with each array element. The rank of an
array is also referred to as the dimensions of the array. An array with a rank of one is called a single-
dimensional array. An array with a rank greater than one is called a multi-dimensional array. Specific sized
multidimensional arrays are often referred to as two-dimensional arrays, three-dimensional arrays, and so on.

Now             let            us           answer             What            are         jagged       arrays?
 A jagged array is an array whose elements are arrays. The elements of jagged array can be of different
dimensions and sizes. A jagged array is sometimes called as ―array-of-arrays‖. It is called jagged because each
of its rows is of different size so the final or graphical representation is not a square.

 When you create a jagged array you declare the number of rows in your array. Each row will hold an array
that will be on any length. Before filling the values in the inner arrays you must declare them.

Jagged array declaration in C#:

For e.g. : int [] [] myJaggedArray = new int [3][];

Declaration of inner arrays:

myJaggedArray[0] = new int[5] ; // First inner array will be of length 5.
myJaggedArray[1] = new int[4] ; // Second inner array will be of length 4.
myJaggedArray[2] = new int[3] ; // Third inner array will be of length 3.

Now to access third element of second row we write:
 int value = myJaggedArray[1][2];
Note that while declaring the array the second dimension is not supplied because this you will declare later on
in the code.

Jagged array are created out of single dimensional arrays so be careful while using them. Don‘t confuse it with
multi-dimensional arrays because unlike them jagged arrays are not rectangular arrays.

For more information on arrays:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/csref/html/vclrfarrayspg.asp

34. What is a delegate, why should you use it and how do you call it ? A delegate is a reference type
that refers to a Shared method of a type or to an instance method of an object. Delegate is like a function
pointer in C and C++. Pointers are used to store the address of a thing. Delegate lets some other code call
your function without needing to know where your function is actually located. All events in .NET actually use
delegates in the background to wire up events. Events are really just a modified form of a delegate. It should
give you an idea of some different areas in which delegates may be appropriate:


        They enable callback functionality in multi-tier applications as demonstrated in the examples above.
         <o:p></o:p>
        The CacheItemRemoveCallback delegate can be used in ASP.NET to keep cached information up to
         date. When the cached information is removed for any reason, the associated callback is exercised
         and could contain a reload of the cached information. <o:p></o:p>
        Use delegates to facilitate asynchronous processing for methods that do not offer asynchronous
         behavior.
        Events use delegates so clients can give the application events to call when the event is fired.
         Exposing custom events within your applications requires the use of delegates.

34. How does the XmlSerializer work? XmlSerializer in the .NET Framework is a great tool to convert Xml
into runtime objects and vice versa

35. If you define integer variable and a object variable and a structure then how those will be
plotted in memory.

Integer , structure – System.ValueType -- Allocated memory on stack , infact integer is primitive type
recognized and allocated memory by compiler itself .

Infact , System.Int32 definition is as follows :

[C#]
[Serializable]
public struct Int32 : IComparable, IFormattable, IConvertible

So , it‘s a struct by definition , which is the same case with various other value types .

Object – Base class , that is by default reference type , so at runtime JIT compiler allocates memory on the
―Heap‖ Data structure .

Reference types are defined as class , derived directly or indirectly by System.ReferenceType
                                           COM And COM+



01. What are different transaction options available for services components ? There are 5
transactions types that can be used with COM+. Whenever an object is registered with COM+ it has to abide
either to these 5 transaction types.

Disabled: - There is no transaction. COM+ does not provide transaction support for this component.

Not Supported: - Component does not support transactions. Hence even if the calling component in the
hierarchy is transaction enabled this component will not participate in the transaction.

Supported: - Components with transaction type supported will be a part of the transaction if the calling
component                      has                    an                   active                    transaction.
If the calling component is not transaction enabled this component will not start a new transaction.

Required: - Components with this attribute require a transaction i.e. either the calling should have a
transaction in place else this component will start a new transaction.

Required New: - Components enabled with this transaction type always require a new transaction.
Components with required new transaction type instantiate a new transaction for themselves every time.



02. Can we use com Components in .net?.How ?.can we use .net components in vb?.Explain how ?
COM components have different internal architecture from .NET components hence they are not innately
compatible. However .NET framework supports invocation of unmanaged code from managed code (and vice-
versa) through COM/.NET interoperability. .NET application communicates with a COM component through a
managed wrapper of the component called Runtime Callable Wrapper (RCW); it acts as managed proxy to the
unmanaged COM component. When a method call is made to COM object, it goes onto RCW and not the object
itself. RCW manages the lifetime management of the COM component. Implementation Steps -

Create Runtime Callable Wrapper out of COM component. Reference the metadata assembly Dll in the project
and use its methods & properties RCW can be created using Type Library Importer utility or through VS.NET.
Using VS.NET, add reference through COM tab to select the desired DLL. VS.NET automatically generates
metadata assembly putting the classes provided by that component into a namespace with the same name as
COM dll (XYZRCW.dll)

.NET components can be invoked by unmanaged code through COM Callable Wrapper (CCW) in COM/.NET
interop. The unmanaged code will talk to this proxy, which translates call to managed environment. We can
use COM components in .NET through COM/.NET interoperability. When managed code calls an unmanaged
component, behind the scene, .NET creates proxy called COM Callable wrapper (CCW), which accepts
commands from a COM client, and forwards it to .NET component. There are two prerequisites to creating .NET
component,              to             be            used            in            unmanaged               code:
1. .NET class should be implement its functionality through interface. First define interface in code, then have
the class to imlpement it. This way, it prevents breaking of COM client, if/when .NET component changes.

2.Secondly, .NET class, which is to be visible to COM clients must be declared public. The tools that create the
CCW                       only                      define                     types                      based
on public classes. The same rule applies to methods, properties, and events that will be used by COM clients.

Implementation Steps - 1. Generate type library of .NET component, using TLBExporter utility. A type library is
the COM equivalent of the metadata contained within a .NET assembly. Type libraries are generally contained
in files with the extension .tlb. A type library contains the necessary information to allow a COM client to
determine which classes are located in a particular server, as well as the methods, properties, and events
supported by those classes. 2. Secondly, use Assembly Registration tool (regasm) to create the type library
and                                                    register                                             it.
3. Lastly install .NET assembly in GAC, so it is available as shared assembly.
03.       What       is      Runtime        Callable     wrapper?.when           it     will       created?.
The common language runtime exposes COM objects through a proxy called the runtime callable wrapper
(RCW). Although the RCW appears to be an ordinary object to .NET clients, its primary function is to marshal
calls between a .NET client and a COM object. This wrapper turns the COM interfaces exposed by the COM
component into .NET-compatible interfaces. For oleautomation (attribute indicates that an interface is
compatible with Automation) interfaces, the RCW can be generated automatically from a type library. For non-
oleautomation interfaces, it may be necessary to develop a custom RCW which manually maps the types
exposed by the COM interface to .NET-compatible types.

04. What is Com Callable wrapper?when it will created? .NET components are accessed from COM via a
COM Callable Wrapper (CCW). This is similar to a RCW, but works in the opposite direction. Again, if the
wrapper cannot be automatically generated by the .NET development tools, or if the automatic behaviour is
not desirable, a custom CCW can be developed. Also, for COM to 'see' the .NET component, the .NET
component must be registered in the registry.CCWs also manage the object identity and object lifetime of the
managed objects they wrap.

05. What is a primary interop ? A primary interop assembly is a collection of types that are deployed,
versioned, and configured as a single unit. However, unlike other managed assemblies, an interop assembly
contains type definitions (not implementation) of types that have already been defined in COM. These type
definitions allow managed applications to bind to the COM types at compile time and provide information to
the common language runtime about how the types should be marshaled at run time.

06. What are tlbimp and tlbexp tools used for ? The Type Library Exporter generates a type library that
describes the types defined in a common language runtime assembly. The Type Library Importer converts the
type definitions found within a COM type library into equivalent definitions in a common language runtime
assembly. The output of Tlbimp.exe is a binary file (an assembly) that contains runtime metadata for the types
defined within the original type library.

07. What benefit do you get from using a Primary Interop Assembly (PIA)? PIAs are important
because they provide unique type identity. The PIA distinguishes the official type definitions from counterfeit
definitions provided by other interop assemblies. Having a single type identity ensures type compatibility
between applications that share the types defined in the PIA. Because the PIA is signed by its publisher and
labeled with the PrimaryInteropAssembly attribute, it can be differentiated from other interop assemblies that
define the same types.




                                          WinForms FAQ :



01. What base class do all Web Forms inherit from?
System.Windows.Forms.Form

02. What is the difference between Debug.Write and Trace.Write? When should each be used? The
Debug.Write call won't be compiled when the DEBUGsymbol is not defined (when doing a release build).
Trace.Write calls will be compiled. Debug.Write is for information you want only in debug builds, Trace.Write is
for when you want it in release build as well.

03. Difference between Anchor and Dock Properties? Dock Property->Gets or sets which edge of the
parent container a control is docked to. A control can be docked to one edge of its parent container or can be
docked to all edges and fill the parent container. For example, if you set this property to DockStyle.Left, the
left                                edge                                   of                               the
control will be docked to the left edge of its parent control. Additionally, the docked edge of the control is
resized               to           match               that             of            its            container
control.
Anchor Property->Gets or sets which edges of the control are anchored to the edges of its container. A control
can be anchored to one or more edges of its parent container. Anchoring a control to its parent ensures that
the anchored edges remain in the same position relative to the edges of the parent container when the parent
container is resized.
04. When would you use ErrorProvider control? ErrorProvider control is used in Windows Forms
application. It is like Validation Control for ASP.NET pages. ErrorProvider control is used to provide validations
in Windows forms and display user friendly messages to the user if the validation fails. E.g If we went to
validate the textBox1 should be empty, then we can validate as below

 1). You need to place the errorprovide control on the form
 private void textBox1_Validating(object sender, System.ComponentModel.CancelEventArgs e)
{
ValidateName();
}
private bool ValidateName()
{
bool bStatus = true;
if (textBox1.Text == "")
{
errorProvider1.SetError (textBox1,"Please enter your Name");
bStatus = false;
}
else
errorProvider1.SetError (textBox1,"");
return bStatus;
}
 it check the textBox1 is empty . If it is empty, then a message Please enter your name is displayed.

05. Can you write a class without specifying namespace? Which namespace does it belong to by
default? Yes, you can, then the class belongs to global namespace which has no name. For commercial
products, naturally, you wouldn't want global namespace.

06. You are designing a GUI application with a windows and several widgets on it. The user then
resizes the app window and sees a lot of grey space, while the widgets stay in place. What's the
problem? One should use anchoring for correct resizing. Otherwise the default property of a widget on a form
is top-left, so it stays at the same location when resized.

07.    How      can   you   save the desired            properties     of   Windows      Forms application?
.config files in .NET are supported through the API to allow storing and retrieving information. They are
nothing more than simple XML files, sort of like what .ini files were before for Win32 apps.

08. So how do you retrieve the customized properties of a .NET application from XML .config file?
Initialize an instance of AppSettingsReader class. Call the GetValue method of AppSettingsReader class,
passing in the name of the property and the type expected. Assign the result to the appropriate variable.

09. Can you automate this process?
In Visual Studio yes, use Dynamic Properties for automatic .config creation, storage and retrieval.

10. My progress bar freezes up and dialog window shows blank, when an intensive background
process takes over.
Yes, you should've multi-threaded your GUI, with taskbar and main form being one thread, and the
background process being the other.

11.         What's       the      safest      way      to     deploy        a  Windows   Forms      app?
Web deployment: the user always downloads the latest version of the code, the program runs within security
sandbox, properly written app will not require additional security privileges.

12. Why is it not a good idea to insert code into InitializeComponent method when working with
Visual                                                                                                 Studio?
The designer will likely through it away, most of the code inside InitializeComponent is auto-generated.

13. What's the difference between WindowsDefaultLocation and WindowsDefaultBounds?
WindowsDefaultLocation tells the form to start up at a location selected by OS, but with internally specified
size. WindowsDefaultBounds delegates both size and starting position choices to the OS.

14. What's the difference between Move and LocationChanged? Resize and Size Changed? Both
methods do the same, Move and Resize are the names adopted from VB to ease migration to C#.
15. How would you create a non-rectangular window, let's say an ellipse? Create a rectangular form,
set the TransparencyKey property to the same value as BackColor, which will effectively make the background
of the form transparent. Then set the FormBorderStyle to FormBorderStyle.None, which will remove
the contour and contents of the form.

16. How do you create a separator in the Menu Designer? A hyphen '-' would do it. Also, an ampersand
'&\' would underline the next letter.

17. How's anchoring different from docking? Anchoring treats the component as having the absolute size
and adjusts its location relative to the parent form. Docking treats the component location as absolute and
disregards the component size. So if a status bar must always be at the bottom no matter what, use docking.
If a button should be on the top right, but change its position with the form being resized, use anchoring.

18.      How        do       you      trigger       the        Paint     event      in      System.Drawing?
Invalidate the current form, the OS will take care of repainting. The Update method forces the repaint.

19. With these events, why wouldn't Microsoft combine Invalidate and Paint, so that you wouldn't
have to tell it to repaint, and then to force it to repaint? Painting is the slowest thing the OS does, so
usually telling it to repaint, but not forcing it allows for the process to take place in the background.

20. How can you assign an RGB color to a System.Drawing.Color object? Call the static method
FromArgb of this class and pass it the RGB values.

21. What class does Icon derive from? Isn't it just a Bitmap with a wrapper name around it? No, Icon
lives in System.Drawing namespace. It's not a Bitmap by default, and is treated separately by .NET. However,
you can use ToBitmap method to get a valid Bitmap object from a valid Icon object.

22. Before in my VB app I would just load the icons from DLL. How can I load the icons provided by
.NET     dynamically?      By    using     System.Drawing.SystemIcons          class, for  example
System.Drawing.SystemIcons.Warning produces an Icon with a warning sign in it.

23. When displaying fonts, what's the difference between pixels, points and ems? A pixel is the
lowest-resolution dot the computer monitor supports. Its size depends on user's settings and monitor
size. A point is always 1/72 of an inch. An em is the number of pixels that it takes to display the letter M.




                                         Remoting FAQ's



01. What distributed process frameworks outside .NET do you know? Distributed Computing
Environment/Remote Procedure Calls (DEC/RPC), Microsoft Distributed Component Object Model (DCOM),
Common Object Request Broker Architecture (CORBA), and Java Remote Method Invocation (RMI).

02. What are possible implementations of distributed applications in .NET? .NET Remoting and
ASP.NET Web Services. If we talk about the Framework Class Library, noteworthy classes are in
 System.Runtime.Remoting and System.Web.Services.

03.     When      would      you     use     .NET     Remoting     and      when       Web       services?
Use remoting for more efficient exchange of information when you control both ends of the application. Use
Web services for   open-protocol-based information exchange when you are just a client or a server with the
other end belonging to someone else.

04.       What's      a      proxy      of      the     server       object     in     .NET       Remoting?
 It's a fake copy of the server object that resides on the client side and behaves as if it was the server. It
handles the communication between real server object and the client object. This process is also known as
marshaling.

05.         What          are         remotable            objects      in        .NET         Remoting?
Remotable objects are the objects that can be marshaled across the application domains. You can marshal by
value, where a deep copy of the object is created and then passed to the receiver. You can also marshal by
reference, where just a reference to an existing object is passed.
06.            What             are             channels          in          .NET            Remoting?
Channels represent the objects that transfer the other serialized objects from one application domain to
another and from one computer to another, as well as one process to another on the same box. A channel
must exist before an object can be transferred.

07. What security measures exist for .NET Remoting in System.Runtime.Remoting?
 None. Security should be taken care of at the application level. Cryptography and other security techniques
can be applied at application or server level.

08. What is a formatter? A formatter is an object that is responsible for encoding and serializing data into
messages on one end, and deserializing and decoding messages into data on the other end.

09. Choosing between HTTP and TCP for protocols and Binary and SOAP for formatters, what are
the trade-offs? Binary over TCP is the most effiecient, SOAP over HTTP is the most interoperable.

10. What's SingleCall activation mode used for? If the server object is instantiated for responding to just
one single request, the request should be made in SingleCall mode.

11. What's Singleton activation mode? A single object is instantiated regardless of the number of clients
accessing it. Lifetime of this object is determined by lifetime lease.

12. How do you define the lease of the object?
By implementing ILease interface when writing the class code.

13. Can you configure a .NET Remoting object via XML file?
Yes, via machine.config and application level .config file (or web.config in ASP.NET). Application-level XML
settings take precedence over machine.config.

14. How can you automatically generate interface for the remotable object in .NET with Microsoft
tools?
Use the Soapsuds tool.

15.          What           are        CAO's         i.e.        Client        Activated           Objects          ?
Client-activated objects are objects whose lifetimes are controlled by the calling application domain, just as
they would be if the object were local to the client. With client activation, a round trip to the server occurs
when the client tries to create an instance of the server object, and the client proxy is created using an object
reference (ObjRef) obtained on return from the creation of the remote object on the server. Each time a client
creates an instance of a client-activated type, that instance will service only that particular reference in that
particular client until its lease expires and its memory is recycled. If a calling application domain creates two
new instances of the remote type, each of the client references will invoke only the particular instance in the
server application domain from which the reference was returned.
In COM, clients hold an object in memory by holding a reference to it. When the last client releases its last
reference, the object can delete itself. Client activation provides the same client control over the server
object's lifetime, but without the complexity of maintaining references or the constant pinging to confirm the
continued existence of the server or client. Instead, client-activated objects use lifetime leases to determine
how long they should continue to exist. When a client creates a remote object, it can specify a default length
of time that the object should exist. If the remote object reaches its default lifetime limit, it contacts the client
to ask whether it should continue to exist, and if so, for how much longer. If the client is not currently
available, a default time is also specified for how long the server object should wait while trying to contact the
client before marking itself for garbage collection. The client might even request an indefinite default lifetime,
effectively preventing the remote object from ever being recycled until the server application domain is torn
down. The difference between this and a server-activated indefinite lifetime is that an indefinite server-
activated object will serve all client requests for that type, whereas the client-activated instances serve only
the client and the reference that was responsible for their creation. For more information, see Lifetime Leases.
To create an instance of a client-activated type, clients either configure their application programmatically (or
using a configuration file) and call new (New in Visual Basic), or they pass the remote object's configuration in
a call to Activator.CreateInstance. The following code example shows such a call, assuming a TcpChannel has
been registered to listen on port 8080.


16. How many processes can listen on a single TCP/IP port?
One.
17.      What       technology       enables         out-of-proc        communication           in      .NET?
Most usually Remoting;.NET remoting enables client applications to use objects in other processes on the same
computer or on any other computer available on its network.While you could implement an out-of-proc
component in any number of other ways, someone using the term almost always means Remoting.

18. How can objects in two diff. App Doimains communicate with each other? .Net framework
provides various ways to communicate with objects in different app domains. First is XML Web Service on
internet, its good method because it is built using HTTP protocol and SOAP formatting.
If the performance is the main concern then go for second option which is .Net remoting because it gives you
the option of using binary encoding and the default TcpChannel, which offers the best interprocess
communication performance
19. What is the difference between .Net Remoting and Web Services? Although we can develop an
application using both technologies, each of them has its distinct advantages. Yes you can look at them in
terms of performance but you need to consider your need first. There are many other factors such
authentications, authorizing in process that need to be considered.

Point                            Remoting                                  Webservices
 If your application needs                                                  Yes, Choose Web Services because
interoperability with other      No                                        it is more flexible in that they are
platforms or operating systems                                             support SOAP.
 If performance is the main       You should use the TCP channel and the
                                                                           No
requirement with security        binary formatter
Complex Programming              Yes                                       No
                                  Supports a range of state management,
                                                                         Its stateless service management
                                 depending on what object lifetime
State Management                                                        (does not inherently correlate
                                 scheme you choose (single call or
                                                                        multiple calls from the same user)
                                 singleton call).
                                  It can access through TCP or HTTP        It can be access only through
Transport Protocol
                                 channel.                                  HTTP channel.




                      Basic .NET and ASP.NET interview questions


     1. How many languages .NET is supporting now? - When .NET was introduced it came with several
        languages. VB.NET, C#, COBOL and Perl, etc. The site DotNetLanguages.Net says 44 languages are
        supported.

   2. How is .NET able to support multiple languages?
      -   a language should comply with the Common Language Runtime standard to become a .NET
          language. In .NET, code is compiled to Microsoft Intermediate Language (MSIL for short). This is
          called as Managed Code. This Managed code is run in .NET environment. So after compilation to this
          IL the language is not a barrier. A code can call or use a function written in another language.
      -
     3. How ASP .NET different from ASP?
        Scripting is separated from the HTML, Code is compiled as a DLL, and these DLLs can be executed on
     the server.

     4. What is smart navigation? - The cursor position is maintained when the page gets refreshed due to
        the server side validation and the page gets refreshed.

     5. What is view state?
      The web is stateless. But in ASP.NET, the state of a page is maintained in the in the page itself
      automatically. How? The values are encrypted and saved in hidden controls. this is done automatically by
      the ASP.NET. This can be switched off / on for a single control
     6. How do you validate the controls in an ASP .NET page?
      -  Using special validation controls that are meant for this. We have Range Validator, Email Validator.

     7. Can the validation be done in the server side? Or this can be done only in the Client side? -
        Client side is done by default. Server side validation is also possible. We can switch off the client side
        and server side can be done.

     8. How to manage pagination in a page?
      -  Using pagination option in DataGrid control. We have to set the number of records for a page, then
         it takes care of pagination by itself.


     9. What is ADO .NET and what is difference between ADO and ADO.NET? - ADO.NET is stateless
        mechanism. I can treat the ADO.Net as a separate in-memory database where in I can use
        relationships between the tables and select insert and updates to the database. I can update the
        actual database as a batch.



   Describe the role of inetinfo.exe, aspnet_isapi.dll andaspnet_wp.exe
    in the page loading process. inetinfo.exe is theMicrosoft IIS server running,
    handling ASP.NET requests among other things.When an ASP.NET request is received (usually a file with
    .aspx extension),the ISAPI filter aspnet_isapi.dll takes
    care of it by passing the request tothe actual worker process aspnet_wp.exe.

   What’s the difference between Response.Write() andResponse.Output.Write()?
    The latter one allows you to write formatted output.

   What methods are fired during the page load? Init() - when the pageis
    instantiated, Load() - when the page is loaded into server memory,PreRender()
    - the brief moment before the page is displayed to the user asHTML, Unload()
    - when page finishes loading.

   Where does the Web page belong in the .NET Framework class hierarchy?System.Web.UI.Page

   Where do you store the information about the user’s locale? System.Web.UI.Page.Culture

   What’s the difference between Codebehind="MyCode.aspx.cs"                     andSrc="MyCode.aspx.cs"?
    CodeBehind is relevant to Visual Studio.NET only.

   What’s       a   bubbled   event?      When       you     have    a    complex      control,   likeDataGrid,
    writing     an    event  processing      routine     for    each    object    (cell,    button,row,     etc.)
    is    quite    tedious.  The     controls     can      bubble    up     their   eventhandlers,      allowing
    the main DataGrid event handler to take care of itsconstituents

   Suppose you want a certain ASP.NET function executed on MouseOver over a
    certain button. Where do you add an event handler? It‘s the Attributesproperty,
    the Add function inside that property. So

       btnSubmit.Attributes.Add("onMouseOver","someClientCode();")A
       simple”Javascript:ClientCode();” in the button control of                                      the
       .aspx
       page will attach the handler (javascript function)to                                           the
       onmouseover event.

   What data type does the RangeValidator control support?
   Integer,String
    and Date.

   Where would you use an iHTTPModule, and what are the limitations of any
    approach you might take in implementing one?
    One of ASP.NET‘s most useful features is the extensibility of the HTTP pipeline, the path that data takes
    between                           client                            and                           server.
    You can use them to extend your ASP.NET applications by adding pre- and post-processing to each HTTP
    request coming into your application. For example, if you wanted custom authentication facilities for your
    application,                         the                         best                           technique
    would     be  to   intercept   the   request  when      it  comes    in  and   process    the      request
    in a custom HTTP module.

   Explain    what       a    diffgram      is    and      a    good     use      for    one?      A    DiffGram      is
    an   XML    format      that    is   used    to    identify    current   and      original    versions    of    data
    elements. The DataSet uses the DiffGram format to load and persist its contents,
    and    to   serialize    its    contents    for     transport    across     a     network     connection.      When
    a   DataSet     is    written     as   a    DiffGram,     it   populates      the    DiffGram      with    all   the
    necessary     information       to    accurately       recreate     the      contents,      though       not     the
    schema,    of     the    DataSet,     including      column     values    from      both     the    Original     and
    Current row versions, row error information, and row order.




                                    ASP.NET DataGrid questions

   What is datagrid? The DataGrid Web server control is a powerful tool for displaying information from a
    data source. It is easy to use; you can display editable data in a professional-looking grid by setting only a
    few properties. At the same time, the grid has a sophisticated object model that provides you with great
    flexibility in how you display the data.

   What’s the difference between the System.Web.UI.WebControls.DataGrid and and
    System.Windows.Forms.DataGrid? The Web UI control does not inherently support master-detail data
    structures. As with other Web server controls, it does not support two-way data binding. If you want to
    update data, you must write code to do this yourself. You can only edit one row at a time. It does not
    inherently support sorting, although it raises events you can handle in order to sort the grid contents. You
    can bind the Web Forms DataGrid to any object that supports the IEnumerable interface. The Web Forms
    DataGrid control supports paging. It is easy to customize the appearance and layout of the Web Forms
    DataGrid control as compared to the Windows Forms one.

   How do you customize the column content inside the datagrid? If you want to customize the content
    of a column, make the column a template column. Template columns work like item templates in the
    DataList or Repeater control, except that you are defining the layout of a column rather than a row.

   How do you apply specific formatting to the data inside the cells? You cannot specify formatting for
    columns generated when the grid‘s AutoGenerateColumns property is set to true, only for bound or
    template columns. To format, set the column‘s DataFormatString property to a string-formatting
    expression suitable for the data type of the data you are formatting.

   How do you hide the columns? One way to have columns appear dynamically is to create them at
    design time, and then to hide or show them as needed. You can do this by setting a column‘s Visible
    property.

   How do you display an editable drop-down list? Displaying a drop-down list requires a template
    column in the grid. Typically, the ItemTemplate contains a control such as a data-bound Label control to
    show the current value of a field in the record. You then add a drop-down list to the EditItemTemplate. In
    Visual Studio, you can add a template column in the Property builder for the grid, and then use standard
    template editing to remove the default TextBox control from the EditItemTemplate and drag a
    DropDownList control into it instead. Alternatively, you can add the template column in HTML view. After
    you have created the template column with the drop-down list in it, there are two tasks. The first is to
    populate the list. The second is to preselect the appropriate item in the list — for example, if a book‘s
    genre is set to ―fiction,‖ when the drop-down list displays, you often want ―fiction‖ to be preselected.

   How do you check whether the row data has been changed? The definitive way to determine
    whether a row has been dirtied is to handle the changed event for the controls in a row. For example, if
    your grid row contains a TextBox control, you can respond to the control‘s TextChanged event. Similarly,
    for check boxes, you can respond to a CheckedChanged event. In the handler for these events, you
    maintain a list of the rows to be updated. Generally, the best strategy is to track the primary keys of the
    affected rows. For example, you can maintain an ArrayList object that contains the primary keys of the
    rows to update.
                              .NET deployment questions


1. What do you know about .NET assemblies?
 Assemblies are the smallest units of versioning and deployment in the .NET application. Assemblies are
also the building blocks for programs such as Web services, Windows services, serviced components, and
.NET remoting applications.

2. What’s the difference between private and shared assembly?
 Private assembly is used inside an application only and does not have to be identified by a strong name.
Shared assembly can be used by multiple applications and has to have a strong name.

3. What’s a strong name?
A strong name includes the name of the assembly, version number, culture identity, and a public key
token.

4. How can you tell the application to look for assemblies at the locations other than its own
   install?
 Use the
directive in the XML .config file for a given application.
           <probing privatePath=‖c:\mylibs; bin\debug‖ />

   should do the trick. Or you can add additional search paths in the Properties box of the deployed
   application.

5. How can you debug failed assembly binds?
 Use the Assembly Binding Log Viewer (fuslogvw.exe) to find out the paths searched.

6. Where are shared assemblies stored?
Global assembly cache.

7. How can you create a strong name for a .NET assembly?
With the help of Strong Name tool (sn.exe).

8. Where’s global assembly cache located on the system? Usually C:\winnt\assembly or
   C:\windows\assembly.

9. Can you have two files with the same file name in GAC?
 Yes, remember that GAC is a very special folder, and while normally you would not be able to place two
files with the same name into a Windows folder, GAC differentiates by version number as well, so it‘s
possible for MyApp.dll and MyApp.dll to co-exist in GAC if the first one is version 1.0.0.0 and the second
one is 1.1.0.0.

10. So let’s say I have an application that uses MyApp.dll assembly, version 1.0.0.0. There is a
    security bug in that assembly, and I publish the patch, issuing it under name MyApp.dll
    1.1.0.0. How do I tell the client applications that are already installed to start using this
    new MyApp.dll?

 Use publisher policy. To configure a publisher policy, use the publisher policy configuration file, which
uses a format similar app .config file. But unlike the app .config file, a publisher policy file needs to be
compiled into an assembly and placed in the GAC.

11. What is delay signing?
 Delay signing allows you to place a shared assembly in the GAC by signing the assembly with just the
public key. This allows the assembly to be signed with the private key at a later stage, when the
development process is complete and the component or assembly is ready to be deployed. This process
enables developers to work with shared assemblies as if they were strongly named, and it secures the
private key of the signature from being accessed at different stages of development.
                             Windows code security questions


     1. What’s the difference between code-based security and role-based security? Which one is
         better?
      Code security is the approach of using permissions and permission sets for a given code to run. The
     admin, for example, can disable running executables off the Internet or restrict access to corporate
     database to only few applications. Role-based security most of the time involves the code running with
     the privileges of the current user. This way the code cannot supposedly do more harm than mess up a
     single user account. There‘s no better, or 100% thumbs-up approach, depending on the nature of
     deployment, both code-based and role-based security could be implemented to an extent.

     2. How can you work with permissions from your .NET application?
     You can request permission to do something and you can demand certain permissions from other apps.
     You can also refuse permissions so that your app is not inadvertently used to destroy some data.


     3. How can C# app request minimum permissions?
                using System.Security.Permissions;
                [assembly:FileDialogPermissionAttribute(SecurityAction.RequestMinimum,
                Unrestricted=true)]

     4. What’s a code group?
     A code group is a set of assemblies that share a security context.

     5. What’s the difference between authentication and authorization?
      Authentication happens first. You verify user‘s identity based on credentials. Authorization is making sure
     the user only gets access to the resources he has credentials for.


     6. What are the authentication modes in ASP.NET?
      None, Windows, Forms and Passport.

     7. Are the actual permissions for the application defined at run-time or compile-time?
      The CLR computes actual permissions at runtime based on code group membership and the calling chain
     of the code.




                                  ASP.NET questions, part 2


Explain the differences between Server-side and Client-side code?
 Server side scripting means that all the script will be executed by the server and interpreted as needed. ASP
doesn‘t have some of the functionality like sockets, uploading, etc. For these you have to make a custom
components usually in VB or VC++. Client side scripting means that the script will be executed immediately in
the browser such as form field validation, clock, email validation, etc. Client side scripting is usually done in
VBScript or JavaScript. Download time, browser compatibility, and visible code - since JavaScript and VBScript
code is included in the HTML page, then anyone can see the code by viewing the page source. Also a possible
security hazards for the client computer.



 What type of code (server or client) is found in a Code-Behind class?
C#

   Should validation (did the user enter a real date) occur server-side or client-side? Why?
 Client-side validation because there is no need to request a server side date when you could obtain a date
from the client machine.
 What does the "EnableViewState" property do? Why would I want it on or off?
Enable ViewState turns on the automatic state management feature that enables server controls to re-
populate their values on a round trip without requiring you to write any code. This feature is not free however,
since the state of a control is passed to and from the server in a hidden form field. You should be aware of
when ViewState is helping you and when it is not. For example, if you are binding a control to data on every
round trip (as in the datagrid example in tip #4), then you do not need the control to maintain it‘s view state,
since you will wipe out any re-populated data in any case. ViewState is enabled for all server controls by
default. To disable it, set the EnableViewState property of the control to false.


   What is the difference between Server.Transfer and Response.Redirect? Why would I choose
    one over the other?
 Server.Transfer() : client is shown as it is on the requesting page only, but the all the content is of the
requested page. Data can be persist accros the pages using Context.Item collection, which is one of the best
way to transfer data from one page to another keeping the page state alive. Response.Dedirect() :client know
the physical loation (page name and query string as well). Context.Items loses the persisitance when nevigate
to destination page. In earlier versions of IIS, if we wanted to send a user to a new Web page, the only option
we had was Response.Redirect. While this method does accomplish our goal, it has several important
drawbacks. The biggest problem is that this method causes each page to be treated as a separate transaction.
Besides making it difficult to maintain your transactional integrity, Response.Redirect introduces some
additional headaches. First, it prevents good encapsulation of code. Second, you lose access to all of the
properties in the Request object. Sure, there are workarounds, but they‘re difficult. Finally, Response.Redirect
necessitates a round trip to the client, which, on high-volume sites, causes scalability problems. As you might
suspect, Server.Transfer fixes all of these problems. It does this by performing the transfer on the server
without requiring a roundtrip to the client.


   Can you give an example of when it would be appropriate to use a web service as opposed to a
    non-serviced .NET component?
When to Use Web Services:

        Communicating through a Firewall When building a distributed application with 100s/1000s of
         users spread over multiple locations, there is always the problem of communicating between client
         and server because of firewalls and proxy servers. Exposing your middle tier components as Web
         Services and invoking the directly from a Windows UI is a very valid option.

        Application Integration When integrating applications written in various languages and running on
         disparate systems. Or even applications running on the same platform that have been written by
         separate vendors.


        Business-to-Business Integration This is an enabler for B2B intergtation which allows one to
         expose vital business processes to authorized supplier and customers. An example would be exposing
         electronic ordering and invoicing, allowing customers to send you purchase orders and suppliers to
         send you invoices electronically.

        Software Reuse This takes place at multiple levels. Code Reuse at the Source code level or binary
         componet-based resuse. The limiting factor here is that you can reuse the code but not the data
         behind it. Webservice overcome this limitation. A scenario could be when you are building an app that
         aggregates the functionality of serveral other Applicatons. Each of these functions could be performed
         by individual apps, but there is value in perhaps combining the the multiple apps to present a unifiend
         view in a Portal or Intranet.


     When not to use Web Services:


     Single machine Applicatons When the apps are running on the same machine and need to
     communicate with each other use a native API. You also have the options of using component
     technologies such as COM or .NET Componets as there is very little overhead.


        Homogeneous Applications on a LAN If you have Win32 or Winforms apps that want to
         communicate to their server counterpart. It is much more efficient to use DCOM in the case of Win32
         apps and .NET Remoting in the case of .NET Apps.
   Can you explain the difference between an ADO.NET Dataset and an ADO Recordset?
 In ADO, the in-memory representation of data is the recordset. In ADO.NET, it is the dataset. There are
important differences between them.

        A recordset looks like a single table. If a recordset is to contain data from multiple database tables, it
         must use a JOIN query, which assembles the data from the various database tables into a single
         result table. In contrast, a dataset is a collection of one or more tables. The tables within a dataset
         are called data tables; specifically, they are DataTable objects. If a dataset contains data from
         multiple database tables, it will typically contain multiple DataTable objects. That is, each DataTable
         object typically corresponds to a single database table or view. In this way, a dataset can mimic the
         structure of the underlying database. A dataset usually also contains relationships. A relationship
         within a dataset is analogous to a foreign-key relationship in a database —that is, it associates rows
         of the tables with each other. For example, if a dataset contains a table about investors and another
         table about each investor‘s stock purchases, it could also contain a relationship connecting each row
         of the investor table with the corresponding rows of the purchase table. Because the dataset can hold
         multiple, separate tables and maintain information about relationships between them, it can hold
         much richer data structures than a recordset, including self-relating tables and tables with many-to-
         many relationships.

        In ADO you scan sequentially through the rows of the recordset using the ADO MoveNext method. In
         ADO.NET, rows are represented as collections, so you can loop through a table as you would through
         any collection, or access particular rows via ordinal or primary key index. DataRelation objects
         maintain information about master and detail records and provide a method that allows you to get
         records related to the one you are working with. For example, starting from the row of the Investor
         table for "Nate Sun," you can navigate to the set of rows of the Purchase table describing his
         purchases. A cursor is a database element that controls record navigation, the ability to update data,
         and the visibility of changes made to the database by other users. ADO.NET does not have an
         inherent cursor object, but instead includes data classes that provide the functionality of a traditional
         cursor. For example, the functionality of a forward-only, read-only cursor is available in the ADO.NET
         DataReader object. For more information about cursor functionality, see Data Access Technologies.


        Minimized Open Connections: In ADO.NET you open connections only long enough to perform a
         database operation, such as a Select or Update. You can read rows into a dataset and then work with
         them without staying connected to the data source. In ADO the recordset can provide disconnected
         access, but ADO is designed primarily for connected access. There is one significant difference
         between disconnected processing in ADO and ADO.NET. In ADO you communicate with the database
         by making calls to an OLE DB provider. In ADO.NET you communicate with the database through a
         data adapter (an OleDbDataAdapter, SqlDataAdapter, OdbcDataAdapter, or OracleDataAdapter
         object), which makes calls to an OLE DB provider or the APIs provided by the underlying data source.
         The important difference is that in ADO.NET the data adapter allows you to control how the changes
         to the dataset are transmitted to the database — by optimizing for performance, performing data
         validation checks, or adding any other extra processing. Data adapters, data connections, data
         commands, and data readers are the components that make up a .NET Framework data provider.
         Microsoft and third-party providers can make available other .NET Framework data providers that can
         be integrated into Visual Studio.


        Sharing Data Between Applications. Transmitting an ADO.NET dataset between applications is much
         easier than transmitting an ADO disconnected recordset. To transmit an ADO disconnected recordset
         from one component to another, you use COM marshalling. To transmit data in ADO.NET, you use a
         dataset, which can transmit an XML stream.


        Richer data types.COM marshalling provides a limited set of data types — those defined by the COM
         standard. Because the transmission of datasets in ADO.NET is based on an XML format, there is no
         restriction on data types. Thus, the components sharing the dataset can use whatever rich set of data
         types they would ordinarily use.


        Performance. Transmitting a large ADO recordset or a large ADO.NET dataset can consume network
         resources; as the amount of data grows, the stress placed on the network also rises. Both ADO and
         ADO.NET let you minimize which data is transmitted. But ADO.NET offers another performance
         advantage, in that ADO.NET does not require data-type conversions. ADO, which requires COM
         marshalling to transmit records sets among components, does require that ADO data types be
         converted to COM data types.
        Penetrating Firewalls.A firewall can interfere with two components trying to transmit disconnected
         ADO recordsets. Remember, firewalls are typically configured to allow HTML text to pass, but to
         prevent system-level requests (such as COM marshalling) from passing.



  Can you give an example of what might be best suited to place in the Application_Start and
   Session_Start subroutines?
The Application_Start event is guaranteed to occur only once throughout the lifetime of the application. It‘s a
good place to initialize global variables. For example, you might want to retrieve a list of products from a
database table and place the list in application state or the Cache object. SessionStateModule exposes both
Session_Start and Session_End events.


  If I’m developing an application that must accomodate multiple security levels though secure
   login and my ASP.NET web appplication is spanned across three web-servers (using round-
   robbin load balancing) what would be the best approach to maintain login-in state for the
   users?
 What are ASP.NET Web Forms? How is this technology different than what is available though
   ASP?
Web Forms are the heart and soul of ASP.NET. Web Forms are the User Interface (UI) elements that give your
Web applications their look and feel. Web Forms are similar to Windows Forms in that they provide properties,
methods, and events for the controls that are placed onto them. However, these UI elements render
themselves in the appropriate markup language required by the request, e.g. HTML. If you use Microsoft Visual
Studio .NET, you will also get the familiar drag-and-drop interface used to create your UI for your Web
application.


  How does VB.NET/C# achieve polymorphism?
By using Abstract classes/functions.

   Can you explain what inheritance is and an example of when you might use it? Inheritance is a
    fundamental feature of an object oriented system and it is simply the ability to inherit data and
    functionality from a parent object. Rather than developing new objects from scratch, new code can be
    based on the work of other programmers, adding only new features that are needed.

   How would you implement inheritance using VB.NET/C#?
When we set out to implement a class using inheritance, we must first start with an existing class from which
we will derive our new subclass. This existing class, or base class, may be part of the .NET system class library
framework, it may be part of some other application or .NET assembly, or we may create it as part of our
existing application. Once we have a base class, we can then implement one or more subclasses based on that
base class. Each of our subclasses will automatically have all of the methods, properties, and events of that
base class ? including the implementation behind each method, property, and event. Our subclass can add new
methods, properties, and events of its own - extending the original interface with new functionality.
Additionally, a subclass can replace the methods and properties of the base class with its own new
implementation - effectively overriding the original behavior and replacing it with new behaviors. Essentially
inheritance is a way of merging functionality from an existing class into our new subclass. Inheritance also
defines rules for how these methods, properties, and events can be merged.




                                  ASP.NET questions, part 3


     1. Whats an assembly?

     Assemblies are the building blocks of .NET Framework applications; they form the fundamental unit of
     deployment, version control, reuse, activation scoping, and security permissions. An assembly is a
     collection of types and resources that are built to work together and form a logical unit of functionality.
     An assembly provides the common language runtime with the information it needs to be aware of type
     implementations. To the runtime, a type does not exist outside the context of an assembly.
2. Describe the difference between inline and code behind - which is best in a loosely coupled
   solution?
 ASP.NET supports two modes of page development: Page logic code that is written inside <script
runat=server> blocks within an .aspx file and dynamically compiled the first time the page is requested
on the server. Page logic code that is written within an external class that is compiled prior to deployment
on a server and linked "behind" the .aspx file at run time.


3. Explain what a diffgram is, and a good use for one?
A DiffGram is an XML format that is used to identify current and original versions of data elements. The
DataSet uses the DiffGram format to load and persist its contents, and to serialize its contents for
transport across a network connection. When a DataSet is written as a DiffGram, it populates the
DiffGram with all the necessary information to accurately recreate the contents, though not the schema,
of the DataSet, including column values from both the Original and Current row versions, row error
information, and row order.

4. Where would you use an iHTTPModule, and what are the limitations of anyapproach you
   might take in implementing one?
One of ASP.NET‘s most useful features is the extensibility of the HTTP pipeline, the path that data takes
between client and server. You can use them to extend your ASP.NET applications by adding pre- and
post-processing to each HTTP request coming into your application. For example, if you wanted custom
authentication facilities for your application, the best technique would be to intercept the request when it
comes in and process the request in a custom HTTP module.


5. What are the disadvantages of viewstate/what are the benefits?

6. Describe session handling in a webfarm, how does it work and what are the limits?

7. How would you get ASP.NET running in Apache web servers - why would you even do this?

8. Whats MSIL, and why should my developers need an appreciation of it if at all?

9. In what order do the events of an ASPX page execute. As a developer is it important to
undertsand these events?

Every Page object (which your .aspx page is) has nine events, most of which you will not have to worry
about in your day to day dealings with ASP.NET. The three that you will deal with the most are:
Page_Init, Page_Load, Page_PreRender.
10. Which method do you invoke on the DataAdapter control to load your generated dataset
   with data?
          System.Data.Common.DataAdapter.Fill(System.Data.DataSet);

   If my DataAdapter is sqlDataAdapter and my DataSet is dsUsers then it is called this way:
          sqlDataAdapter.Fill(dsUsers);

data in the Repeater control?


11. Which template must you provide, in order to display data in a Repeater control?
    ItemTemplate


12. How can you provide an alternating color scheme in a Repeater control?
    AlternatingItemTemplate Like the ItemTemplate element, but rendered for every other
    row (alternating items) in the Repeater control. You can specify a different appearance
    for the AlternatingItemTemplate element by setting its style properties.


13. What property must you set, and what method must you call in your code, in order to bind
    the data from some data source to the Repeater control?
    You must set the DataMember property which Gets or sets the specific table in the DataSource to bind
    to the control and the DataBind method to bind data from a source to a server control. This method is
    commonly used after retrieving a data set through a database query.
14. What base class do all Web Forms inherit from?
System.Web.UI.Page

15. What method do you use to explicitly kill a user’s session?
    The Abandon method destroys all the objects stored in a Session object and releases their resources.
    If you do not call the Abandon method explicitly, the server destroys these objects when the session
    times out.

Syntax: Session.Abandon


16. How do you turn off cookies for one page in your site?
    Use the Cookie.Discard Property which Gets or sets the discard flag set by the server. When true, this
    property instructs the client application not to save the Cookie on the user‘s hard disk when a session
    ends.

17. Which two properties are on every validation control?
ControlToValidate & ErrorMessage properties

18. What tags do you need to add within the asp:datagrid tags to bind columns manually?

19. How do you create a permanent cookie?
 Setting the Expires property to MinValue means that the Cookie never expires.


20. What tag do you use to add a hyperlink column to the DataGrid?

21. What is the standard you use to wrap up a call to a Web service?

22. Which method do you use to redirect the user to another page without performing a round
    trip to the client?
 Server.transfer()


23. What is the transport protocol you use to call a Web service?

 SOAP. Transport Protocols: It is essential for the acceptance of Web Services that they are based on
established Internet infrastructure. This in fact imposes the usage of of the HTTP, SMTP and FTP protocols
based on the TCP/IP family of transports. Messaging Protocol: The format of messages exchanged
between Web Services clients and Web Services should be vendor neutral and should not carry details
about the technology used to implement the service. Also, the message format should allow for
extensions and different bindings to specific transport protocols. SOAP and ebXML Transport are
specifications which fulfill these requirements. We expect that the W3C XML Protocol Working Group
defines a successor standard.


24. True or False: A Web service can only be written in .NET.
 False.

25. What does WSDL stand for?
Web Services Description Language

26. What property do you have to set to tell the grid which page to go to when using the Pager
    object?

27. Where on the Internet would you look for Web services?

 UDDI repositaries like uddi.microsoft.com, IBM UDDI node, UDDI Registries in Google Directory,
enthusiast sites like XMethods.net.


28. What tags do you need to add within the asp:datagrid tags to bind columns manually?
    Column tag and an ASP:databound tag.
29. Which property on a Combo Box do you set with a column name, prior to setting the
    DataSource, to display data in the combo box?


30. How is a property designated as read-only? In VB.NET:
             Public ReadOnly Property PropertyName As ReturnType
                   Get         ‗Your Property Implementation goes in here
                   End Get
             End Property

   in C#
             public returntype PropertyName
             {
                   get{
                         //property implementation goes here
                   }
                   // Do not write the set implementation
             }




31. Which control would you use if you needed to make sure the values in two different
    controls matched?

Use the CompareValidator control to compare the values of 2 different controls.



True or False:

To test a Web service you must create a windows application or Web application to consume
this service?
 False.



32. How many classes can a single .NET DLL contain?


Unlimited.
                              Operating System



1. What are the basic functions of an operating system? - Operating system controls and
   coordinates the use of the hardware among the various applications programs for various
   uses. Operating system acts as resource allocator and manager. Since there are many
   possibly conflicting requests for resources the operating system must decide which requests
   are allocated resources to operating the computer system efficiently and fairly. Also
   operating system is control program which controls the user programs to prevent errors and
   improper use of the computer. It is especially concerned with the operation and control of
   I/O devices.




2. Why paging is used? - Paging is solution to external fragmentation problem which is to
   permit the logical address space of a process to be noncontiguous, thus allowing a process
   to be allocating physical memory wherever the latter is available.




3. While running DOS on a PC, which command would be used to duplicate the entire
   diskette? diskcopy




4. What resources are used when a thread created? How do they differ from those
   when a process is created? - When a thread is created the threads does not require any
   new resources to execute the thread shares the resources like memory of the process to
   which they belong to. The benefit of code sharing is that it allows an application to have
   several different threads of activity all within the same address space. Whereas if a new
   process creation is very heavyweight because it always requires new address space to be
   created and even if they share the memory then the inter process communication is
   expensive when compared to the communication between the threads.




5. What is virtual memory? - Virtual memory is hardware technique where the system
   appears to have more memory that it actually does. This is done by time-sharing, the
   physical memory and storage parts of the memory one disk when they are not actively
   being used.




6. What is Throughput, Turnaround time, waiting time and Response time? -
   Throughput – number of processes that complete their execution per time unit. Turnaround
   time – amount of time to execute a particular process. Waiting time – amount of time a
   process has been waiting in the ready queue. Response time – amount of time it takes from
   when a request was submitted until the first response is produced, not output (for time-
   sharing environment).




7. What is the state of the processor, when a process is waiting for some event to
   occur? - Waiting state
8. What is the important aspect of a real-time system or Mission Critical Systems? - A
   real time operating system has well defined fixed time constraints. Process must be done
   within the defined constraints or the system will fail. An example is the operating system for
   a flight control computer or an advanced jet airplane. Often used as a control device in a
   dedicated application such as controlling scientific experiments, medical imaging systems,
   industrial control systems, and some display systems. Real-Time systems may be either
   hard or soft real-time.

Hard real-time: Secondary storage limited or absent, data stored in short term memory, or
read-only memory (ROM), Conflicts with time-sharing systems, not supported by general-
purpose operating systems.

 Soft real-time: Limited utility in industrial control of robotics, Useful in applications
(multimedia, virtual reality) requiring advanced operating-system features.




9. What is the difference between Hard and Soft real-time systems? - A hard real-time
   system guarantees that critical tasks complete on time. This goal requires that all delays in
   the system be bounded from the retrieval of the stored data to the time that it takes the
   operating system to finish any request made of it. A soft real time system where a critical
   real-time task gets priority over other tasks and retains that priority until it completes. As in
   hard real time systems kernel delays need to be bounded




10. What is the cause of thrashing? How does the system detect thrashing? Once it
    detects thrashing, what can the system do to eliminate this problem? - Thrashing is
    caused by under allocation of the minimum number of pages required by a process, forcing
    it to continuously page fault. The system can detect thrashing by evaluating the level of CPU
    utilization as compared to the level of multiprogramming. It can be eliminated by reducing
    the level of multiprogramming.




11. What is multi tasking, multi programming, multi threading? - Multi programming:
    Multiprogramming is the technique of running several programs at a time using
    timesharing. It allows a computer to do several things at the same time. Multiprogramming
    creates logical parallelism. The concept of multiprogramming is that the operating system
    keeps several jobs in memory simultaneously. The operating system selects a job from the
    job pool and starts executing a job, when that job needs to wait for any i/o operations the
    CPU is switched to another job. So the main idea here is that the CPU is never idle.




Multi tasking: Multitasking is the logical extension of multiprogramming .The concept of
multitasking is quite similar to multiprogramming but difference is that the switching between
jobs occurs so frequently that the users can interact with each program while it is running. This
concept is also known as time-sharing systems. A time-shared operating system uses CPU
scheduling and multiprogramming to provide each user with a small portion of time-shared
system.
 Multi threading: An application typically is implemented as a separate process with several
threads of control. In some situations a single application may be required to perform several
similar tasks for example a web server accepts client requests for web pages, images, sound,
and so forth. A busy web server may have several of clients concurrently accessing it. If the web
server ran as a traditional single-threaded process, it would be able to service only one client at
a time. The amount of time that a client might have to wait for its request to be serviced could
be enormous. So it is efficient to have one process that contains multiple threads to serve the
same purpose. This approach would multithread the web-server process, the server would
create a separate thread that would listen for client requests when a request was made rather
than creating another process it would create another thread to service the request. To get the
advantages like responsiveness, Resource sharing economy and utilization of multiprocessor
architectures multithreading concept can be used.




12. What is hard disk and what is its purpose? - Hard disk is the secondary storage device,
    which holds the data in bulk, and it holds the data on the magnetic medium of the disk.Hard
    disks have a hard platter that holds the magnetic medium, the magnetic medium can be
    easily erased and rewritten, and a typical desktop machine will have a hard disk with a
    capacity of between 10 and 40 gigabytes. Data is stored onto the disk in the form of files

.

13. What is fragmentation? Different types of fragmentation? - Fragmentation occurs in a
    dynamic memory allocation system when many of the free blocks are too small to satisfy
    any request.

 External Fragmentation: External Fragmentation happens when a dynamic memory
allocation algorithm allocates some memory and a small piece is left over that cannot be
effectively used. If too much external fragmentation occurs, the amount of usable memory is
drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous.

Internal Fragmentation: Internal fragmentation is the space wasted inside of allocated
memory blocks because of restriction on the allowed sizes of allocated blocks. Allocated memory
may be slightly larger than requested memory; this size difference is memory internal to a
partition, but not being used




14. What is DRAM? In which form does it store data? - DRAM is not the best, but it‘s cheap,
    does the job, and is available almost everywhere you look. DRAM data resides in a cell
    made of a capacitor and a transistor. The capacitor tends to lose data unless it‘s recharged
    every couple of milliseconds, and this recharging tends to slow down the performance of
    DRAM compared to speedier RAM types.




15. What is Dispatcher? - Dispatcher module gives control of the CPU to the process selected
    by the short-term scheduler; this involves: Switching context, Switching to user mode,
    Jumping to the proper location in the user program to restart that program, dispatch
    latency – time it takes for the dispatcher to stop one process and start another running.
16. What is CPU Scheduler? - Selects from among the processes in memory that are ready to
    execute, and allocates the CPU to one of them. CPU scheduling decisions may take place
    when a process: 1.Switches from running to waiting state. 2.Switches from running to ready
    state. 3.Switches from waiting to ready. 4.Terminates. Scheduling under 1 and 4 is non-
    preemptive. All other scheduling is preemptive.




17. What is Context Switch? - Switching the CPU to another process requires saving the state
    of the old process and loading the saved state for the new process. This task is known as a
    context switch. Context-switch time is pure overhead, because the system does no useful
    work while switching. Its speed varies from machine to machine, depending on the memory
    speed, the number of registers which must be copied, the existed of special
    instructions(such as a single instruction to load or store all registers).




18. What is cache memory? - Cache memory is random access memory (RAM) that a
    computer microprocessor can access more quickly than it can access regular RAM. As the
    microprocessor processes data, it looks first in the cache memory and if it finds the data
    there (from a previous reading of data), it does not have to do the more time-consuming
    reading of data from larger memory.




19. What is a Safe State and what is its use in deadlock avoidance? - When a process
    requests an available resource, system must decide if immediate allocation leaves the
    system in a safe state. System is in safe state if there exists a safe sequence of all
    processes. Deadlock Avoidance: ensure that a system will never enter an unsafe state.




20. What is a Real-Time System? - A real time process is a process that must respond to the
    events within a certain time period. A real time operating system is an operating system
    that can run real time processes successfully




                                   Linux Internals



21. How do you list the files in an UNIX directory while also showing hidden files? ls -
     ltra




22. How do you execute a UNIX command in the background? Use the ―&‖.
23. What UNIX command will control the default file permissions when files are
    created? umask




24. Explain the read, write, and execute permissions on a UNIX directory. Read allows
     you to see and list the directory contents. Write allows you to create, edit and delete files
     and subdirectories in the directory. Execute gives you the permissions to run programs or
     shells from the directory.




25. What is the difference between a soft link and a hard link? A symbolic (soft) linked file
    and the targeted file can be located on the same or different file system while for a hard link
    they must be located on the same file system.




26. Give the command to display space usage on the UNIX file system. df -lk




27. Explain iostat, vmstat and netstat. iostat reports on terminal, disk and tape I/O activity.
     vmstat reports on virtual memory statistics for processes, disk, tape and CPU activity.
     netstat reports on the contents of network data structures.




28. How would you change all occurrences of a value using VI? %s/(old value)/(new
     value)/g




29. Give two UNIX kernel parameters that effect an Oracle install. SHMMAX & SHMMNI




30. Briefly, how do you install Oracle software on UNIX? Basically, set up disks, kernel
     parameters, and run orainst.
   31. first command:
       ls -a (or -A if you don‘t care about . and .. directories). -l gives more detail, r reverses sort
       order, t sorts by modification time. They are unimportant to the question, the only thing that
       matters is the a parameter.




ls ................. show directory, in alphabetical order
logout ............. logs off system
mkdir .............. make a directory
rmdir .............. remove directory (rm -r to delete folders with files)
rm ................. remove files
cd ................. change current directory
man (command) ...... shows help on a specific command
talk (user) ........ pages user for chat - (user) is a email address
write (user) ....... write a user on the local system (control-c to
 end)
pico (filename) .... easy to use text editor to edit files
pine ............... easy to use mailer
more (file) ........ views a file, pausing every screenful
sz ................. send a file (to you) using zmodem
rz ................. recieve a file (to the unix system) using zmodem
telnet (host) ...... connect to another Internet site
ftp (host) ......... connects to a FTP site
archie (filename) .. search the Archie database for a file on a FTP site
irc ................ connect to Internet Relay Chat
lynx ............... a textual World Wide Web browser
gopher ............. a Gopher database browser
tin, trn ........... read Usenet newsgroups

passwd ............. change your password
chfn ............... change your "Real Name" as seen on finger
chsh ............... change the shell you log into
grep ............... search for a string in a file
tail ............... show the last few lines of a file
who ................ shows who is logged into the local system
w ..................
 shows who is logged on and what they're doing
finger (emailaddr).. shows more information about a user
df ................. shows disk space available on the system
du ................. shows how much disk space is being used up by folders
chmod .............. changes permissions on a file
bc ................. a simple calculator
make ............... compiles source
 code
gcc (file.c) ....... compiles C source into a file named 'a.out'
gzip ............... best compression for UNIX files
zip ................ zip for IBM files
tar ................ combines multiple files into one or vice-versa
lharc, lzh, lha .... un-arc'ers, may not be on your system
dos2unix (file) (new) - strips CR's out of dos text files
unix2dos (file) (new) - adds CR's to unix text files

				
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