Namespaces
Variants
Views
Actions

Standard library header <set>

From cppreference.com
< cpp‎ | header
 
 
Standard Library headers
Note: a slash '/' in a revision mark means that the header was deprecated and/or removed.
Language support
Concepts
<concepts> (C++20)
Diagnostics
<system_error> (C++11)

Memory management
<memory_resource> (C++17)  
Metaprogramming
<type_traits> (C++11)
<ratio> (C++11)
General utilities
<utility>
<tuple> (C++11)
<optional> (C++17)
<variant> (C++17)
<any> (C++17)
<expected> (C++23)
<bitset>

<charconv> (C++17)
<format> (C++20)
<bit> (C++20)

Strings
<cuchar> (C++11)

Containers
<flat_set> (C++23)
<span> (C++20)
<mdspan> (C++23)

Iterators
<iterator>
Ranges
<ranges> (C++20)
<generator> (C++23)
Algorithms
Numerics
<cfenv> (C++11)
<complex>
<numbers> (C++20)

Time
<chrono> (C++11)
Localization
<codecvt> (C++11/17)
Input/output
<filesystem> (C++17)
<cstdio>
<cinttypes> (C++11)
<strstream> (C++98/)
Regular expressions
<regex> (C++11)
Concurrency support
<stop_token> (C++20)
<thread> (C++11)
<atomic> (C++11)
<stdatomic.h> (C++23)
<mutex> (C++11)
<shared_mutex> (C++14)
<condition_variable> (C++11)  
<semaphore> (C++20)
<latch> (C++20)
<barrier> (C++20)
<future> (C++11)

C compatibility
<cstdbool> (C++11/17/20)  
<ccomplex> (C++11/17/20)
<ctgmath> (C++11/17/20)

<cstdalign> (C++11/17/20)

<ciso646> (until C++20)

 

This header is part of the containers library.

Contents

Includes

(C++20)
Three-way comparison operator support [edit]
std::initializer_list class template [edit]

Classes

collection of unique keys, sorted by keys
(class template) [edit]
collection of keys, sorted by keys
(class template) [edit]

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 in the set
(function template) [edit]
specializes the std::swap algorithm
(function template) [edit]
Erases all elements satisfying specific criteria
(function template) [edit]
(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 in the multiset
(function template) [edit]
specializes the std::swap algorithm
(function template) [edit]
Erases all elements satisfying specific criteria
(function template) [edit]
Range access
(C++11)(C++14)
returns an iterator to the beginning of a container or array
(function template) [edit]
(C++11)(C++14)
returns an iterator to the end of a container or array
(function template) [edit]
returns a reverse iterator to the beginning of a container or array
(function template) [edit]
(C++14)
returns a reverse end iterator for a container or array
(function template) [edit]
(C++17)(C++20)
returns the size of a container or array
(function template) [edit]
(C++17)
checks whether the container is empty
(function template) [edit]
(C++17)
obtains the pointer to the underlying array
(function template) [edit]

[edit] 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>>;
  }
}

[edit] 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 InputIt>
      set(InputIt first, InputIt 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 InputIt>
      set(InputIt first, InputIt 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
    [[nodiscard]] 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);
    iterator insert(const_iterator position, const value_type& x);
    iterator insert(const_iterator position, value_type&& x);
    template<class InputIt>
      void insert(InputIt first, InputIt 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 InputIt,
           class Compare = less<__iter_value_type<InputIt>>,
           class Allocator = allocator<__iter_value_type<InputIt>>>
    set(InputIt, InputIt,
        Compare = Compare(), Allocator = Allocator())
      -> set<__iter_value_type<InputIt>, 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 InputIt, class Allocator>
    set(InputIt, InputIt, Allocator)
      -> set<__iter_value_type<InputIt>,
             less<__iter_value_type<InputIt>>, 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>;
}

[edit] 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 InputIt>
      multiset(InputIt first, InputIt 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 InputIt>
      multiset(InputIt first, InputIt 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
    [[nodiscard]] 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 InputIt>
      void insert(InputIt first, InputIt 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 InputIt,
           class Compare = less<__iter_value_type<InputIt>>,
           class Allocator = allocator<__iter_value_type<InputIt>>>
    multiset(InputIt, InputIt,
             Compare = Compare(), Allocator = Allocator())
      -> multiset<__iter_value_type<InputIt>, 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 InputIt, class Allocator>
    multiset(InputIt, InputIt, Allocator)
      -> multiset<__iter_value_type<InputIt>,
                  less<__iter_value_type<InputIt>>, 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>;
}

[edit] 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