Standard library header <map>

 

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Standard library headers

Language support <cfloat> <climits> <compare>(C++20) <contracts>(C++26) <coroutine>(C++20) <csetjmp> <csignal> <cstdarg> <cstddef> <cstdint>(C++11) <cstdlib> <exception> <initializer_list>(C++11)    <limits> <new> <source_location>(C++20) <stdfloat>(C++23) <typeinfo> <version>(C++20) Concepts <concepts>(C++20) Diagnostics <cassert> <cerrno> <debugging>(C++26) <stacktrace>(C++23) <stdexcept> <system_error>(C++11) Memory management <memory> <memory_resource>(C++17) <scoped_allocator>(C++11) Metaprogramming <type_traits>(C++11) <ratio>(C++11)

General utilities <any>(C++17) <bitset> <bit>(C++20) <charconv>(C++17) <expected>(C++23) <format>(C++20) <functional> <optional>(C++17) <stdbit.h>(C++26) <tuple>(C++11) <typeindex>(C++11) <utility> <variant>(C++17) Containers <array>(C++11) <deque> <flat_map>(C++23) <flat_set>(C++23) <forward_list>(C++11) <hive>(C++26) <inplace_vector>(C++26)    <list> <map> <mdspan>(C++23) <queue> <set> <span>(C++20) <stack> <unordered_map>(C++11) <unordered_set>(C++11) <vector> Iterators <iterator> Ranges <generator>(C++23) <ranges>(C++20)

Algorithms <algorithm> <numeric> Strings <cctype> <cstring> <cuchar>(C++11) <cwchar> <cwctype> <string_view>(C++17) <string> Text processing <clocale> <codecvt>(C++11/17/26*) <locale> <regex>(C++11) <text_encoding>(C++26)    Numerics <cfenv>(C++11) <cmath> <complex> <linalg>(C++26) <numbers>(C++20) <random>(C++11) <simd>(C++26) <stdckdint.h>(C++26) <valarray> Time <chrono>(C++11) <ctime> C compatibility <ccomplex>(C++11/17/20*) <ciso646>(until C++20) <cstdalign>(C++11/17/20*) <cstdbool>(C++11/17/20*) <ctgmath>(C++11/17/20*)

Input/output <cinttypes>(C++11) <cstdio> <filesystem>(C++17) <fstream> <iomanip> <iosfwd> <iostream> <ios> <istream> <ostream> <print>(C++23) <spanstream>(C++23) <sstream> <streambuf> <strstream>(C++98/26*) <syncstream>(C++20) Concurrency support <atomic>(C++11) <barrier>(C++20) <condition_variable>(C++11) <future>(C++11) <hazard_pointer>(C++26) <latch>(C++20) <mutex>(C++11) <rcu>(C++26) <semaphore>(C++20) <shared_mutex>(C++14) <stdatomic.h>(C++23) <stop_token>(C++20) <thread>(C++11) Execution support <execution>(C++17)

 

This header is part of the containers library.

Includes
<compare> (C++20)	Three-way comparison operator support
<initializer_list> (C++11)	std::initializer_list class template
Classes
map	collection of key-value pairs, sorted by keys, keys are unique (class template)
multimap	collection of key-value pairs, sorted by keys (class template)
Functions
operator==operator!=operator<operator<=operator>operator>=operator<=> (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)
std::swap(std::map)	specializes the std::swap algorithm (function template)
erase_if(std::map) (C++20)	erases all elements satisfying specific criteria (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (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 multimaps (function template)
std::swap(std::multimap)	specializes the std::swap algorithm (function template)
erase_if(std::multimap) (C++20)	erases all elements satisfying specific criteria (function template)
Range access
begincbegin (C++11)(C++14)	returns an iterator to the beginning of a container or array (function template)
endcend (C++11)(C++14)	returns an iterator to the end of a container or array (function template)
rbegincrbegin (C++14)	returns a reverse iterator to the beginning of a container or array (function template)
rendcrend (C++14)	returns a reverse end iterator for a container or array (function template)
sizessize (C++17)(C++20)	returns the size of a container or array (function template)
empty (C++17)	checks whether the container is empty (function template)
data (C++17)	obtains the pointer to the underlying array (function template)

Synopsis

#include <compare>#include <initializer_list>   namespace std {// class template maptemplate<class Key, class T, class Compare = less<Key>, class Allocator = allocator<pair<const Key, T>>>class map;   template<class Key, class T, class Compare, class Allocator>bool operator==(const map<Key, T, Compare, Allocator>& x, const map<Key, T, Compare, Allocator>& y);template<class Key, class T, class Compare, class Allocator>/*synth-three-way-result*/<pair<const Key, T>> operator<=>(const map<Key, T, Compare, Allocator>& x, const map<Key, T, Compare, Allocator>& y);   template<class Key, class T, class Compare, class Allocator>void swap(map<Key, T, Compare, Allocator>& x, map<Key, T, Compare, Allocator>& y)noexcept(noexcept(x.swap(y)));   // erasure for maptemplate<class Key, class T, class Compare, class Allocator, class Predicate>typename map<Key, T, Compare, Allocator>::size_type erase_if( map<Key, T, Compare, Allocator>& c, Predicate pred);   // class template multimaptemplate<class Key, class T, class Compare = less<Key>, class Allocator = allocator<pair<const Key, T>>>class multimap;   template<class Key, class T, class Compare, class Allocator>bool operator==(const multimap<Key, T, Compare, Allocator>& x, const multimap<Key, T, Compare, Allocator>& y);template<class Key, class T, class Compare, class Allocator>/*synth-three-way-result*/<pair<const Key, T>> operator<=>(const multimap<Key, T, Compare, Allocator>& x, const multimap<Key, T, Compare, Allocator>& y);   template<class Key, class T, class Compare, class Allocator>void swap(multimap<Key, T, Compare, Allocator>& x, multimap<Key, T, Compare, Allocator>& y)noexcept(noexcept(x.swap(y)));   // erasure for multimaptemplate<class Key, class T, class Compare, class Allocator, class Predicate>typename multimap<Key, T, Compare, Allocator>::size_type erase_if( multimap<Key, T, Compare, Allocator>& c, Predicate pred);   namespace pmr {template<class Key, class T, class Compare = less<Key>>using map =std::map<Key, T, Compare, polymorphic_allocator<pair<const Key, T>>>;   template<class Key, class T, class Compare = less<Key>>using multimap =std::multimap<Key, T, Compare, polymorphic_allocator<pair<const Key, T>>>;}}

Class template std::map

namespace std {template<class Key, class T, class Compare = less<Key>, class Allocator = allocator<pair<const Key, T>>>class map {public:// typesusing key_type = Key;using mapped_type = T;using value_type = pair<const Key, T>;using key_compare = Compare;using allocator_type = Allocator;using pointer =typename allocator_traits<Allocator>::pointer;using const_pointer =typename allocator_traits<Allocator>::const_pointer;using reference = value_type&;using const_reference =const value_type&;using size_type =/* implementation-defined */;using difference_type =/* implementation-defined */;using iterator =/* implementation-defined */;using const_iterator =/* implementation-defined */;using reverse_iterator =std::reverse_iterator<iterator>;using const_reverse_iterator =std::reverse_iterator<const_iterator>;using node_type =/* unspecified */;using insert_return_type =/*insert-return-type*/<iterator, node_type>;   class value_compare {protected: Compare comp; value_compare(Compare c): comp(c){}   public:bool operator()(const value_type& x, const value_type& y)const{return comp(x.first, y.first);}};   // construct/copy/destroy map(): map(Compare()){}explicit map(const Compare& comp, const Allocator&= Allocator());template<class InputIter> map(InputIter first, InputIter last, const Compare& comp = Compare(), const Allocator&= Allocator());template<container-compatible-range<value_type> R> map(from_range_t, R&& rg, const Compare& comp = Compare(), const Allocator&= Allocator()); map(const map& x); map(map&& x);explicit map(const Allocator&); map(const map&, const type_identity_t<Allocator>&); map(map&&, const type_identity_t<Allocator>&); map(initializer_list<value_type>, const Compare&= Compare(), const Allocator&= Allocator());template<class InputIter> map(InputIter first, InputIter last, const Allocator& a): map(first, last, Compare(), a){}template<container-compatible-range<value_type> R> map(from_range_t, R&& rg, const Allocator& a)): map(from_range, std::forward<R>(rg), Compare(), a){} map(initializer_list<value_type> il, const Allocator& a): map(il, Compare(), a){} ~map(); map& operator=(const map& x); map& operator=(map&& x)noexcept(allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_move_assignable_v<Compare>); map& operator=(initializer_list<value_type>); allocator_type get_allocator()constnoexcept;   // iterators iterator begin()noexcept; const_iterator begin()constnoexcept; iterator end()noexcept; const_iterator end()constnoexcept;   reverse_iterator rbegin()noexcept; const_reverse_iterator rbegin()constnoexcept; reverse_iterator rend()noexcept; const_reverse_iterator rend()constnoexcept;   const_iterator cbegin()constnoexcept; const_iterator cend()constnoexcept; const_reverse_iterator crbegin()constnoexcept; const_reverse_iterator crend()constnoexcept;   // capacitybool empty()constnoexcept; size_type size()constnoexcept; size_type max_size()constnoexcept;   // element access mapped_type& operator[](const key_type& x); mapped_type& operator[](key_type&& x);template<class K> mapped_type& operator[](K&& x); mapped_type& at(const key_type& x);const mapped_type& at(const key_type& x)const;template<class K> mapped_type& at(const K& x);template<class K>const mapped_type& at(const K& x)const;   // modifierstemplate<class... Args> pair<iterator, bool> emplace(Args&&... args);template<class... Args> iterator emplace_hint(const_iterator position, Args&&... args); pair<iterator, bool> insert(const value_type& x); pair<iterator, bool> insert(value_type&& x);template<class P> pair<iterator, bool> insert(P&& x); iterator insert(const_iterator position, const value_type& x); iterator insert(const_iterator position, value_type&& x);template<class P> iterator insert(const_iterator position, P&&);template<class InputIter>void insert(InputIter first, InputIter last);template<container-compatible-range<value_type> R>void insert_range(R&& rg);void insert(initializer_list<value_type>);   node_type extract(const_iterator position); node_type extract(const key_type& x);template<class K> node_type extract(K&& x); insert_return_type insert(node_type&& nh); iterator insert(const_iterator hint, node_type&& nh);   template<class... Args> pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);template<class... Args> pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);template<class K, class... Args> pair<iterator, bool> try_emplace(K&& k, Args&&... args);template<class... Args> iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);template<class... Args> iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);template<class K, class... Args> iterator try_emplace(const_iterator hint, K&& k, Args&&... args);template<class M> pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);template<class M> pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);template<class K, class M> pair<iterator, bool> insert_or_assign(K&& k, M&& obj);template<class M> iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);template<class M> iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);template<class K, class M> iterator insert_or_assign(const_iterator hint, K&& k, M&& obj);   iterator erase(iterator position); iterator erase(const_iterator position); size_type erase(const key_type& x);template<class K> size_type erase(K&& x); iterator erase(const_iterator first, const_iterator last);void swap(map&)noexcept(allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_swappable_v<Compare>);void clear()noexcept;   template<class C2>void merge(map<Key, T, C2, Allocator>& source);template<class C2>void merge(map<Key, T, C2, Allocator>&& source);template<class C2>void merge(multimap<Key, T, C2, Allocator>& source);template<class C2>void merge(multimap<Key, T, C2, Allocator>&& source);   // observers key_compare key_comp()const; value_compare value_comp()const;   // map operations iterator find(const key_type& x); const_iterator find(const key_type& x)const;template<class K> iterator find(const K& x);template<class K> const_iterator find(const K& x)const;   size_type count(const key_type& x)const;template<class K> size_type count(const K& x)const;   bool contains(const key_type& x)const;template<class K>bool contains(const K& x)const;   iterator lower_bound(const key_type& x); const_iterator lower_bound(const key_type& x)const;template<class K> iterator lower_bound(const K& x);template<class K> const_iterator lower_bound(const K& x)const;   iterator upper_bound(const key_type& x); const_iterator upper_bound(const key_type& x)const;template<class K> iterator upper_bound(const K& x);template<class K> const_iterator upper_bound(const K& x)const;   pair<iterator, iterator> equal_range(const key_type& x); pair<const_iterator, const_iterator> equal_range(const key_type& x)const;template<class K> pair<iterator, iterator> equal_range(const K& x);template<class K> pair<const_iterator, const_iterator> equal_range(const K& x)const;};   template<class InputIter, class Compare = less</*iter-key-type*/<InputIter>>, class Allocator = allocator</*iter-to-alloc-type*/<InputIter>>> map(InputIter, InputIter, Compare = Compare(), Allocator = Allocator())-> map</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, Compare, Allocator>;   template<ranges::input_range R, class Compare = less</*range-key-type*/<R>, class Allocator = allocator</*range-to-alloc-type*/<R>>> map(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())-> map</*range-key-type*/<R>, /*range-mapped-type*/<R>, Compare, Allocator>;   template<class Key, class T, class Compare = less<Key>, class Allocator = allocator<pair<const Key, T>>> map(initializer_list<pair<Key, T>>, Compare = Compare(), Allocator = Allocator())-> map<Key, T, Compare, Allocator>;   template<class InputIter, class Allocator> map(InputIter, InputIter, Allocator)-> map</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, less</*iter-key-type*/<InputIter>>, Allocator>;   template<ranges::input_range R, class Allocator> map(from_range_t, R&&, Allocator)-> map</*range-key-type*/<R>, /*range-mapped-type*/<R>, less</*range-key-type*/<R>>, Allocator>;   template<class Key, class T, class Allocator> map(initializer_list<pair<Key, T>>, Allocator)-> map<Key, T, less<Key>, Allocator>;}

Class template std::multimap

namespace std {template<class Key, class T, class Compare = less<Key>, class Allocator = allocator<pair<const Key, T>>>class multimap {public:// typesusing key_type = Key;using mapped_type = T;using value_type = pair<const Key, T>;using key_compare = Compare;using allocator_type = Allocator;using pointer =typename allocator_traits<Allocator>::pointer;using const_pointer =typename allocator_traits<Allocator>::const_pointer;using reference = value_type&;using const_reference =const value_type&;using size_type =/* implementation-defined */;using difference_type =/* implementation-defined */;using iterator =/* implementation-defined */;using const_iterator =/* implementation-defined */;using reverse_iterator =std::reverse_iterator<iterator>;using const_reverse_iterator =std::reverse_iterator<const_iterator>;using node_type =/* unspecified */;   class value_compare {protected: Compare comp; value_compare(Compare c): comp(c){}   public:bool operator()(const value_type& x, const value_type& y)const{return comp(x.first, y.first);}};   // construct/copy/destroy multimap(): multimap(Compare()){}explicit multimap(const Compare& comp, const Allocator&= Allocator());template<class InputIter> multimap(InputIter first, InputIter last, const Compare& comp = Compare(), const Allocator&= Allocator());template<container-compatible-range<value_type> R> multimap(from_range_t, R&& rg, const Compare& comp = Compare(), const Allocator&= Allocator()); multimap(const multimap& x); multimap(multimap&& x);explicit multimap(const Allocator&); multimap(const multimap&, const type_identity_t<Allocator>&); multimap(multimap&&, const type_identity_t<Allocator>&); multimap(initializer_list<value_type>, const Compare&= Compare(), const Allocator&= Allocator());template<class InputIter> multimap(InputIter first, InputIter last, const Allocator& a): multimap(first, last, Compare(), a){}template<container-compatible-range<value_type> R> multimap(from_range_t, R&& rg, const Allocator& a)): multimap(from_range, std::forward<R>(rg), Compare(), a){} multimap(initializer_list<value_type> il, const Allocator& a): multimap(il, Compare(), a){} ~multimap(); multimap& operator=(const multimap& x); multimap& operator=(multimap&& x)noexcept( allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_move_assignable_v<Compare>); multimap& operator=(initializer_list<value_type>); allocator_type get_allocator()constnoexcept;   // iterators iterator begin()noexcept; const_iterator begin()constnoexcept; iterator end()noexcept; const_iterator end()constnoexcept;   reverse_iterator rbegin()noexcept; const_reverse_iterator rbegin()constnoexcept; reverse_iterator rend()noexcept; const_reverse_iterator rend()constnoexcept;   const_iterator cbegin()constnoexcept; const_iterator cend()constnoexcept; const_reverse_iterator crbegin()constnoexcept; const_reverse_iterator crend()constnoexcept;   // capacitybool empty()constnoexcept; size_type size()constnoexcept; size_type max_size()constnoexcept;   // modifierstemplate<class... Args> iterator emplace(Args&&... args);template<class... Args> iterator emplace_hint(const_iterator position, Args&&... args); iterator insert(const value_type& x); iterator insert(value_type&& x);template<class P> iterator insert(P&& x); iterator insert(const_iterator position, const value_type& x); iterator insert(const_iterator position, value_type&& x);template<class P> iterator insert(const_iterator position, P&& x);template<class InputIter>void insert(InputIter first, InputIter last);template<container-compatible-range<value_type> R>void insert_range(R&& rg);void insert(initializer_list<value_type>);   node_type extract(const_iterator position); node_type extract(const key_type& x);template<class K> node_type extract(K&& x); iterator insert(node_type&& nh); iterator insert(const_iterator hint, node_type&& nh);   iterator erase(iterator position); iterator erase(const_iterator position); size_type erase(const key_type& x);template<class K> size_type erase(K&& x); iterator erase(const_iterator first, const_iterator last);void swap(multimap&)noexcept(allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_swappable_v<Compare>);void clear()noexcept;   template<class C2>void merge(multimap<Key, T, C2, Allocator>& source);template<class C2>void merge(multimap<Key, T, C2, Allocator>&& source);template<class C2>void merge(map<Key, T, C2, Allocator>& source);template<class C2>void merge(map<Key, T, C2, Allocator>&& source);   // observers key_compare key_comp()const; value_compare value_comp()const;   // map operations iterator find(const key_type& x); const_iterator find(const key_type& x)const;template<class K> iterator find(const K& x);template<class K> const_iterator find(const K& x)const;   size_type count(const key_type& x)const;template<class K> size_type count(const K& x)const;   bool contains(const key_type& x)const;template<class K>bool contains(const K& x)const;   iterator lower_bound(const key_type& x); const_iterator lower_bound(const key_type& x)const;template<class K> iterator lower_bound(const K& x);template<class K> const_iterator lower_bound(const K& x)const;   iterator upper_bound(const key_type& x); const_iterator upper_bound(const key_type& x)const;template<class K> iterator upper_bound(const K& x);template<class K> const_iterator upper_bound(const K& x)const;   pair<iterator, iterator> equal_range(const key_type& x); pair<const_iterator, const_iterator> equal_range(const key_type& x)const;template<class K> pair<iterator, iterator> equal_range(const K& x);template<class K> pair<const_iterator, const_iterator> equal_range(const K& x)const;};   template<class InputIter, class Compare = less</*iter-key-type*/<InputIter>>, class Allocator = allocator</*iter-to-alloc-type*/<InputIter>>> multimap(InputIter, InputIter, Compare = Compare(), Allocator = Allocator())-> multimap</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, Compare, Allocator>;   template<ranges::input_range R, class Compare = less</*range-key-type*/<R>>, class Allocator = allocator</*range-to-alloc-type*/<R>>> multimap(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())-> multimap</*range-key-type*/<R>, /*range-mapped-type*/<R>, Compare, Allocator>;   template<class Key, class T, class Compare = less<Key>, class Allocator = allocator<pair<const Key, T>>> multimap(initializer_list<pair<Key, T>>, Compare = Compare(), Allocator = Allocator())-> multimap<Key, T, Compare, Allocator>;   template<class InputIter, class Allocator> multimap(InputIter, InputIter, Allocator)-> multimap</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, less</*iter-key-type*/<InputIter>>, Allocator>;   template<ranges::input_range R, class Allocator> multimap(from_range_t, R&&, Allocator)-> multimap</*range-key-type*/<R>, /*range-mapped-type*/<R>, less</*range-key-type*/<R>>, Allocator>;   template<class Key, class T, class Allocator> multimap(initializer_list<pair<Key, T>>, Allocator)-> multimap<Key, T, less<Key>, Allocator>;}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 133	C++98	map::get_allocator was missing in the synopsis	added