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Standard library headers

Language support <cfloat> <climits> <compare> (C++20) <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) <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) <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) <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
set	collection of unique keys, sorted by keys (class template)
multiset	collection of keys, 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 sets (function template)
std::swap(std::set)	specializes the std::swap algorithm (function template)
erase_if(std::set) (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 multisets (function template)
std::swap(std::multiset)	specializes the std::swap algorithm (function template)
erase_if(std::multiset) (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 set
  template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
  class set;
 
  template<class Key, class Compare, class Allocator>
  bool operator==(const set<Key, Compare, Allocator>& x,
                  const set<Key, Compare, Allocator>& y);
  template<class Key, class Compare, class Allocator>
  /*synth-three-way-result*/<Key> operator<=>(const set<Key, Compare, Allocator>& x,
                                              const set<Key, Compare, Allocator>& y);
 
  template<class Key, class Compare, class Allocator>
  void swap(set<Key, Compare, Allocator>& x,
            set<Key, Compare, Allocator>& y) noexcept(noexcept(x.swap(y)));
 
  // erasure for set
  template<class Key, class Compare, class Allocator, class Predicate>
  typename set<Key, Compare, Allocator>::size_type erase_if(
    set<Key, Compare, Allocator>& c,
    Predicate pred);
 
  // class template multiset
  template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
  class multiset;
 
  template<class Key, class Compare, class Allocator>
  bool operator==(const multiset<Key, Compare, Allocator>& x,
                  const multiset<Key, Compare, Allocator>& y);
  template<class Key, class Compare, class Allocator>
  /*synth-three-way-result*/<Key> operator<=>(const multiset<Key, Compare, Allocator>& x,
                                              const multiset<Key, Compare, Allocator>& y);
 
  template<class Key, class Compare, class Allocator>
  void swap(multiset<Key, Compare, Allocator>& x,
            multiset<Key, Compare, Allocator>& y) noexcept(noexcept(x.swap(y)));
 
  // erasure for multiset
  template<class Key, class Compare, class Allocator, class Predicate>
  typename multiset<Key, Compare, Allocator>::size_type erase_if(
    multiset<Key, Compare, Allocator>& c,
    Predicate pred);
 
  namespace pmr {
    template<class Key, class Compare = less<Key>>
    using set = std::set<Key, Compare, polymorphic_allocator<Key>>;
 
    template<class Key, class Compare = less<Key>>
    using multiset = std::multiset<Key, Compare, polymorphic_allocator<Key>>;
  }
}

Class template std::set

namespace std {
  template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
  class set
  {
  public:
    // types
    using key_type               = Key;
    using key_compare            = Compare;
    using value_type             = Key;
    using value_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>;
 
    // construct/copy/destroy
    set()
      : set(Compare())
    {
    }
    explicit set(const Compare& comp, const Allocator& = Allocator());
    template<class InputIter>
    set(InputIter first,
        InputIter last,
        const Compare& comp = Compare(),
        const Allocator&    = Allocator());
    template<container-compatible-range<value_type> R>
    set(from_range_t,
        R&& rg,
        const Compare& comp = Compare(),
        const Allocator&    = Allocator());
    set(const set& x);
    set(set&& x);
    explicit set(const Allocator&);
    set(const set&, const type_identity_t<Allocator>&);
    set(set&&, const type_identity_t<Allocator>&);
    set(initializer_list<value_type>,
        const Compare&   = Compare(),
        const Allocator& = Allocator());
    template<class InputIter>
    set(InputIter first, InputIter last, const Allocator& a)
      : set(first, last, Compare(), a)
    {
    }
    template<container-compatible-range<value_type> R>
      set(from_range_t, R&& rg, const Allocator& a))
        : set(from_range, std::forward<R>(rg), Compare(), a)
    {
    }
    set(initializer_list<value_type> il, const Allocator& a)
      : set(il, Compare(), a)
    {
    }
    ~set();
    set& operator=(const set& x);
    set& operator=(set&& x) noexcept(allocator_traits<Allocator>::is_always_equal::value&&
                                       is_nothrow_move_assignable_v<Compare>);
    set& 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>
    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 K>
    pair<iterator, bool> insert(K&& x);
    iterator insert(const_iterator position, const value_type& x);
    iterator insert(const_iterator position, value_type&& x);
    template<class K>
    iterator insert(const_iterator position, K&& 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);
    insert_return_type insert(node_type&& nh);
    iterator insert(const_iterator hint, node_type&& nh);
 
    iterator erase(iterator position)
      requires(!same_as<iterator, const_iterator>);
    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(set&) noexcept(allocator_traits<Allocator>::is_always_equal::value&&
                               is_nothrow_swappable_v<Compare>);
    void clear() noexcept;
 
    template<class C2>
    void merge(set<Key, C2, Allocator>& source);
    template<class C2>
    void merge(set<Key, C2, Allocator>&& source);
    template<class C2>
    void merge(multiset<Key, C2, Allocator>& source);
    template<class C2>
    void merge(multiset<Key, C2, Allocator>&& source);
 
    // observers
    key_compare key_comp() const;
    value_compare value_comp() const;
 
    // set 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-value-type*/<InputIter>>,
           class Allocator = allocator</*iter-value-type*/<InputIter>>>
  set(InputIter, InputIter, Compare = Compare(), Allocator = Allocator())
    -> set</*iter-value-type*/<InputIter>, Compare, Allocator>;
 
  template<ranges::input_range R,
           class Compare   = less<ranges::range_value_t<R>>,
           class Allocator = allocator<ranges::range_value_t<R>>>
  set(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())
    -> set<ranges::range_value_t<R>, Compare, Allocator>;
 
  template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
  set(initializer_list<Key>, Compare = Compare(), Allocator = Allocator())
    -> set<Key, Compare, Allocator>;
 
  template<class InputIter, class Allocator>
  set(InputIter, InputIter, Allocator) -> set</*iter-value-type*/<InputIter>,
                                              less</*iter-value-type*/<InputIter>>,
                                              Allocator>;
 
  template<ranges::input_range R, class Allocator>
  set(from_range_t, R&&, Allocator)
    -> set<ranges::range_value_t<R>, less<ranges::range_value_t<R>>, Allocator>;
 
  template<class Key, class Allocator>
  set(initializer_list<Key>, Allocator) -> set<Key, less<Key>, Allocator>;
}

Class template std::multiset

namespace std {
  template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
  class multiset
  {
  public:
    // types
    using key_type               = Key;
    using key_compare            = Compare;
    using value_type             = Key;
    using value_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 */;
 
    // construct/copy/destroy
    multiset()
      : multiset(Compare())
    {
    }
    explicit multiset(const Compare& comp, const Allocator& = Allocator());
    template<class InputIter>
    multiset(InputIter first,
             InputIter last,
             const Compare& comp = Compare(),
             const Allocator&    = Allocator());
    template<container-compatible-range<value_type> R>
    multiset(from_range_t,
             R&& rg,
             const Compare& comp = Compare(),
             const Allocator&    = Allocator());
    multiset(const multiset& x);
    multiset(multiset&& x);
    explicit multiset(const Allocator&);
    multiset(const multiset&, const type_identity_t<Allocator>&);
    multiset(multiset&&, const type_identity_t<Allocator>&);
    multiset(initializer_list<value_type>,
             const Compare&   = Compare(),
             const Allocator& = Allocator());
    template<class InputIter>
    multiset(InputIter first, InputIter last, const Allocator& a)
      : multiset(first, last, Compare(), a)
    {
    }
    template<container-compatible-range<value_type> R>
      multiset(from_range_t, R&& rg, const Allocator& a))
        : multiset(from_range, std::forward<R>(rg), Compare(), a)
    {
    }
    multiset(initializer_list<value_type> il, const Allocator& a)
      : multiset(il, Compare(), a)
    {
    }
    ~multiset();
    multiset& operator=(const multiset& x);
    multiset& operator=(multiset&& x) noexcept(
      allocator_traits<Allocator>::is_always_equal::value&&
        is_nothrow_move_assignable_v<Compare>);
    multiset& 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);
    iterator insert(const_iterator position, const value_type& x);
    iterator insert(const_iterator position, value_type&& 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)
      requires(!same_as<iterator, const_iterator>);
    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(multiset&) noexcept(allocator_traits<Allocator>::is_always_equal::value&&
                                    is_nothrow_swappable_v<Compare>);
    void clear() noexcept;
 
    template<class C2>
    void merge(multiset<Key, C2, Allocator>& source);
    template<class C2>
    void merge(multiset<Key, C2, Allocator>&& source);
    template<class C2>
    void merge(set<Key, C2, Allocator>& source);
    template<class C2>
    void merge(set<Key, C2, Allocator>&& source);
 
    // observers
    key_compare key_comp() const;
    value_compare value_comp() const;
 
    // set 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-value-type*/<InputIter>>,
           class Allocator = allocator</*iter-value-type*/<InputIter>>>
  multiset(InputIter, InputIter, Compare = Compare(), Allocator = Allocator())
    -> multiset</*iter-value-type*/<InputIter>, Compare, Allocator>;
 
  template<ranges::input_range R,
           class Compare   = less<ranges::range_value_t<R>>,
           class Allocator = allocator<ranges::range_value_t<R>>>
  multiset(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())
    -> multiset<ranges::range_value_t<R>, Compare, Allocator>;
 
  template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
  multiset(initializer_list<Key>, Compare = Compare(), Allocator = Allocator())
    -> multiset<Key, Compare, Allocator>;
 
  template<class InputIter, class Allocator>
  multiset(InputIter, InputIter, Allocator)
    -> multiset</*iter-value-type*/<InputIter>,
                less</*iter-value-type*/<InputIter>>,
                Allocator>;
 
  template<ranges::input_range R, class Allocator>
  multiset(from_range_t, R&&, Allocator)
    -> multiset<ranges::range_value_t<R>, less<ranges::range_value_t<R>>, Allocator>;
 
  template<class Key, class Allocator>
  multiset(initializer_list<Key>, Allocator) -> multiset<Key, 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 214	C++98	the declarations of the members find, lower_bound, upper_bound and equal_range of std::set and std::multiset in the synopsis did not match the requirements on associative containers	corrected