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					Version Control




                  26-Jan-11
        Why version control?
   Scenario 1:
       Your program is working
       You change “just one thing”
       Your program breaks
       You change it back
       Your program is still broken--why?

   Has this ever happened to you?




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        Why version control? (part 2)
   Your program worked well enough yesterday
   You made a lot of improvements last night...
       ...but you haven't gotten them to work yet
   You need to turn in your program now

   Has this ever happened to you?




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        Version control for teams
   Scenario:
       You change one part of a program--it works
       Your co-worker changes another part--it works
       You put them together--it doesn’t work
       Some change in one part must have broken something in the
        other part
       What were all the changes?




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        Teams (part 2)
   Scenario:
       You make a number of improvements to a class
       Your co-worker makes a number of different improvements
        to the same class
   How can you merge these changes?




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      diff tools
   There are a number of tools that help you spot changes
    (differences) between two files
   Tools include diff, rcsdiff, jDiff, etc.
   Of course, they won't help unless you kept a copy of the
    older version
   Differencing tools are useful for finding a small number
    of differences in a few files




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        jDiff
   jDiff is a plugin for the jEdit editor
   Advantages:
       Everything is color coded
       Uses synchronized scrolling
       It's inside an editor--you can make changes directly
   Disadvantages:
       Not stand-alone, but must be used within jDiff
       Just a diff tool, not a complete solution




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jDiff




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        Version control systems
   A version control system (often called a source code
    control system) does these things:
       Keeps multiple (older and newer) versions of everything (not
        just source code)
       Requests comments regarding every change
       Allows “check in” and “check out” of files so you know
        which files someone else is working on
       Displays differences between versions




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        sccs
   sccs is Source Code Control System (UNIX)
   sccs keeps multiple versions of a complete directory
   Storage requirements are small, because sccs:
       keeps the original documents
       keeps the changes needed to go from one version to the next
       generates any version when you ask for it




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        rcs
   rcs is Revision Control System (also UNIX)
   rcs is like sccs, and does the same things, but
       sccs keeps the originals, and applies changes to get to newer
        versions
       rcs keeps the current versions, and applies changes to get back
        to older versions
   (Opinion) You usually want to work with the newer
    versions, so rcs is usually the better choice




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        rcs commands
   Create a directory for your rcs files
   co -l file -- check out a file and lock it
       Locking means you can check the file back in
   ci file -- check in a revision (put file under rcs control)
   rcs -l file -- lock a file you already checked out
       (Needed when you checked it out and forgot the -l )
   rcsdiff files -- report differences between files
   merge files -- merges two files into original file
       Not magic--you have to check the results


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      Who cares about UNIX?
   CVS (Concurrent Versions System) is the most popular
    version control system on Windows
   CVS is built on top of rcs
   CVS is built into JBuilder and Eclipse
   “There are two ways to run CVS on Windows 95/NT.
    The first is as a client, talking to a CVS server on a
    Unix box. This is the recommended setup and is
    commonly used.”
      -- http://www.cvshome.org/dev/codewindow.html


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        CVS commands
   cvs checkout file
   cvs commit file
   cvs diff file
   These are CVS commands under UNIXPopular GUIs
    on Windows:
       tkCVS
       jCVS
       WinCVS




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     CVS home page

   http://www.cvshome.org




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The End




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