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multimap
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set
stack
vector map class template
map <map>
comparison operators Map
map::map
map::~map Maps are a kind of associative containers that stores elements formed by the combination of a key value and a mapped value.
member functions:
map::begin In a map, the key value is generally used to uniquely identify the element, while the mapped value is some sort of value
map::clear associated to this key. Types of key and mapped value may differ. For example, a typical example of a map is a telephone guide
map::count where the name is the key and the telephone number is the mapped value.
map::empty
map::end Internally, the elements in the map are sorted from lower to higher key value following a specific strict weak ordering criterion
map::equal_range set on construction.
map::erase
map::find As associative containers, they are especially designed to be efficient accessing its elements by their key (unlike sequence
map::get_allocator
containers, which are more efficient accessing elements by their relative or absolute position).
map::insert
map::key_comp
Therefore, the main characteristics of a map as an associative container are:
map::lower_bound
map::max_size
map::operator= Unique key values: no two elements in the map have keys that compare equal to each other. For a similar associative
map::operator[] container allowing for multiple elements with equivalent keys, see multimap.
map::rbegin Each element is composed of a key and a mapped value. For a simpler associative container where the element value
map::rend itself is its key, see set.
map::size Elements follow a strict weak ordering at all times. Unordered associative arrays, like unordered_map, are available in
map::swap implementations following TR1.
map::upper_bound
map::value_comp
Maps are also unique among associative containers in that they implement the direct access operator (operator[]) which allows
for direct access of the mapped value.
In their implementation in the C++ Standard Template Library, map containers take four template parameters:
1 template < class Key, class T, class Compare = less<Key>,
2 class Allocator = allocator<pair<const Key,T> > > class map;
Where the template parameters have the following meanings:
Key: Type of the key values. Each element in a map is uniquely identified by its key value.
T: Type of the mapped value. Each element in a map is used to store some data as its mapped value.
Compare: Comparison class: A class that takes two arguments of the key type and returns a bool. The expression
comp(a,b), where comp is an object of this comparison class and a and b are key values, shall return true if a is to be
placed at an earlier position than b in a strict weak ordering operation. This can either be a class implementing a function
call operator or a pointer to a function (see constructor for an example). This defaults to less<Key>, which returns the
same as applying the less-than operator (a<b).
The map object uses this expression to determine the position of the elements in the container. All elements in a map
container are ordered following this rule at all times.
Allocator: Type of the allocator object used to define the storage allocation model. By default, the allocator class
template is used, which defines the simplest memory allocation model and is value-independent.
In the reference for the map member functions, these same names (Key, T, Compare and Allocator) are assumed for the
template parameters.
This container class supports bidirectional iterators.
Iterators to elements of map containers access to both the key and the mapped value. For this, the class defines what is called its
value_type, which is a pair class with its first value corresponding to the const version of the key type (template parameter
Key) and its second value corresponding to the mapped value (template parameter T):
typedef pair<const Key, T> value_type;
Iterators of a map container point to elements of this value_type. Thus, for an iterator called it that points to an element of a
map, its key and mapped value can be accessed respectively with:
1 map<Key,T>::iterator it;
2 (*it).first; // the key value (of type Key)
3 (*it).second; // the mapped value (of type T)
4 (*it); // the "element value" (of type pair<const Key,T>)
Naturally, any other direct access operator, such as -> or [] can be used, for example:
1 it->first; // same as (*it).first (the key value)
2 it->second; // same as (*it).second (the mapped value)
Member functions
(constructor) Construct map (public member function)
(destructor) Map destructor (public member function)
operator= Copy container content (public member function)
Iterators:
begin Return iterator to beginning (public member function)
end Return iterator to end (public member function)
rbegin Return reverse iterator to reverse beginning (public member function)
rend Return reverse iterator to reverse end (public member function)
Capacity:
empty Test whether container is empty (public member function)
size Return container size (public member function)
max_size Return maximum size (public member function)
Element access:
operator[] Access element (public member function)
Modifiers:
insert Insert element (public member function)
erase Erase elements (public member function)
swap Swap content (public member function)
clear Clear content (public member function)
Observers:
key_comp Return key comparison object (public member function)
value_comp Return value comparison object (public member function)
Operations:
find Get iterator to element (public member function)
count Count elements with a specific key (public member function)
lower_bound Return iterator to lower bound (public member function)
upper_bound Return iterator to upper bound (public member function)
equal_range Get range of equal elements (public member function)
Allocator:
get_allocator Get allocator (public member function)
Member types
of template <class Key, class T, class Compare=less<Key>, class Allocator=allocator<pair <const Key, T> > >
class map;
member type definition
key_type Key
mapped_type T
value_type pair<const Key,T>
key_compare Compare
value_compare Nested class to compare elements (see member function value_comp)
allocator_type Allocator
reference Allocator::reference
const_reference Allocator::const_reference
iterator Bidirectional iterator
const_iterator Constant bidirectional iterator
size_type Unsigned integral type (usually same as size_t)
difference_type Signed integral type (usually same as ptrdiff_t)
pointer Allocator::pointer
const_pointer Allocator::const_pointer
reverse_iterator reverse_iterator<iterator>
const_reverse_iterator reverse_iterator<const_iterator>
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