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)

 

See More

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 map
  template<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 map
  template<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 multimap
  template<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 multimap
  template<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:
    // types
    using 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() const noexcept;

    // iterators
    iterator begin() noexcept;
    const_iterator begin() const noexcept;
    iterator end() noexcept;
    const_iterator end() const noexcept;

    reverse_iterator rbegin() noexcept;
    const_reverse_iterator rbegin() const noexcept;
    reverse_iterator rend() noexcept;
    const_reverse_iterator rend() const noexcept;

    const_iterator cbegin() const noexcept;
    const_iterator cend() const noexcept;
    const_reverse_iterator crbegin() const noexcept;
    const_reverse_iterator crend() const noexcept;

    // capacity
    bool empty() const noexcept;
    size_type size() const noexcept;
    size_type max_size() const noexcept;

    // 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;

    // modifiers
    template<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:
    // types
    using 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() const noexcept;

    // iterators
    iterator begin() noexcept;
    const_iterator begin() const noexcept;
    iterator end() noexcept;
    const_iterator end() const noexcept;

    reverse_iterator rbegin() noexcept;
    const_reverse_iterator rbegin() const noexcept;
    reverse_iterator rend() noexcept;
    const_reverse_iterator rend() const noexcept;

    const_iterator cbegin() const noexcept;
    const_iterator cend() const noexcept;
    const_reverse_iterator crbegin() const noexcept;
    const_reverse_iterator crend() const noexcept;

    // capacity
    bool empty() const noexcept;
    size_type size() const noexcept;
    size_type max_size() const noexcept;

    // modifiers
    template<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