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Difference between revisions of "cpp/container/map"

From cppreference.com
< cpp‎ | container
(Added description of what unique means)
(+pmr)
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{{cpp/title|map}}
 
{{cpp/title|map}}
 
{{cpp/container/map/navbar}}
 
{{cpp/container/map/navbar}}
−
{{ddcl | header=map |
+
{{dcl begin}}
 +
{{dcl header|map}}
 +
{{dcl | num=1|
 
template<
 
template<
 
     class Key,
 
     class Key,
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> class map;
 
> class map;
 
}}  
 
}}  
 +
{{dcl|num=2|since=c++17|1=
 +
namespace pmr {
 +
    template <class Key, class T, class Compare = std::less<Key>>
 +
    using map = std::map<Key, T, Compare,
 +
                        std::polymorphic_allocator<std::pair<const Key,T>>>
 +
}
 +
}}
 +
{{dcl end}}
  
 
{{tt|std::map}} is a sorted associative container that contains key-value pairs with unique keys. Keys are sorted by using the comparison function {{tt|Compare}}.  Search, removal, and insertion operations have logarithmic complexity. Maps are usually implemented as [[enwiki:Red–black_tree|red-black trees]].
 
{{tt|std::map}} is a sorted associative container that contains key-value pairs with unique keys. Keys are sorted by using the comparison function {{tt|Compare}}.  Search, removal, and insertion operations have logarithmic complexity. Maps are usually implemented as [[enwiki:Red–black_tree|red-black trees]].

Revision as of 07:13, 16 March 2016

 
C++
 
Containers library
 
std::map
Member functions
Non-member functions
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Deduction guides (C++17)
 
Defined in header <map>
template<

    class Key,
    class T,
    class Compare = std::less<Key>,
    class Allocator = std::allocator<std::pair<const Key, T> >

> class map;
 (1)
namespace pmr {

    template <class Key, class T, class Compare = std::less<Key>>
    using map = std::map<Key, T, Compare,
                         std::polymorphic_allocator<std::pair<const Key,T>>>

}
 (2) (since C++17)

std::map is a sorted associative container that contains key-value pairs with unique keys. Keys are sorted by using the comparison function Compare. Search, removal, and insertion operations have logarithmic complexity. Maps are usually implemented as red-black trees.

Everywhere the standard library uses the Template:concept concept, uniqueness is determined by using the equivalence relation. In imprecise terms, two objects a and b are considered equivalent (not unique) if neither compares less than the other: !comp(a, b) && !comp(b, a).

std::map meets the requirements of Template:concept, Template:concept, Template:concept and Template:concept.

Contents

Member types

Member type Definition
key_type Key[edit]
mapped_type T[edit]
value_type std::pair<const Key, T>[edit]
size_type Unsigned integer type (usually std::size_t)[edit]
difference_type Signed integer type (usually std::ptrdiff_t)[edit]
key_compare Compare[edit]
allocator_type Allocator[edit]
reference value_type&[edit]
const_reference const value_type&[edit]
pointer

Allocator::pointer

(until C++11)

std::allocator_traits<Allocator>::pointer

(since C++11)
[edit]
const_pointer

Allocator::const_pointer

(until C++11)

std::allocator_traits<Allocator>::const_pointer

(since C++11)
[edit]
iterator LegacyBidirectionalIterator to value_type[edit]
const_iterator LegacyBidirectionalIterator to const value_type[edit]
reverse_iterator std::reverse_iterator<iterator>[edit]
const_reverse_iterator std::reverse_iterator<const_iterator>[edit]

Member classes

 compares objects of type value_type
(class) [edit]

Member functions

 constructs the map
(public member function) [edit]
destructs the map
(public member function) [edit]
assigns values to the container
(public member function) [edit]
returns the associated allocator
(public member function) [edit]
Element access
access specified element with bounds checking
(public member function) [edit]
access or insert specified element
(public member function) [edit]
Iterators
(C++11)
 returns an iterator to the beginning
(public member function) [edit]
(C++11)
 returns an iterator to the end
(public member function) [edit]
(C++11)
 returns a reverse iterator to the beginning
(public member function) [edit]
(C++11)
 returns a reverse iterator to the end
(public member function) [edit]
Capacity
checks whether the container is empty
(public member function) [edit]
returns the number of elements
(public member function) [edit]
returns the maximum possible number of elements
(public member function) [edit]
Modifiers
clears the contents
(public member function) [edit]
inserts elements or nodes(since C++17)
(public member function) [edit]
(C++17)
 inserts an element or assigns to the current element if the key already exists
(public member function) [edit]
(C++11)
 constructs element in-place
(public member function) [edit]
(C++11)
 constructs elements in-place using a hint
(public member function) [edit]
(C++17)
 inserts in-place if the key does not exist, does nothing if the key exists
(public member function) [edit]
erases elements
(public member function) [edit]
swaps the contents
(public member function) [edit]
Lookup
returns the number of elements matching specific key
(public member function) [edit]
finds element with specific key
(public member function) [edit]
returns range of elements matching a specific key
(public member function) [edit]
returns an iterator to the first element not less than the given key
(public member function) [edit]
returns an iterator to the first element greater than the given key
(public member function) [edit]
Observers
returns the function that compares keys
(public member function) [edit]
returns the function that compares keys in objects of type value_type
(public member function) [edit]

Non-member functions

(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)
 lexicographically compares the values of two maps
(function template) [edit]
specializes the std::swap algorithm
(function template) [edit]
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