Standard library header <unordered_set>

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

Standard Library header files

Language Support
<cstddef> <limits> <climits> <contract>	<cfloat> <cstdint> <new> <version>	<typeinfo> <exception> <initializer_list>	<csignal> <csetjmp> <cstdarg>
Concepts
<concepts>
Diagnostics
<stdexcept>	<cassert>	<cerrno>	<system_error>
General utilities
<utility> <memory> <memory_resource> <scoped_allocator> <compare>	<bitset> <tuple> <optional> <any> <variant>	<type_traits> <ratio> <chrono> <typeindex> <functional>	<ctime> <cstdlib>
Strings
<string> <string_view>	<cctype> <cwctype>	<cwchar> <cuchar>	<cstring> <charconv>
Localization
<locale>	<codecvt>	<clocale>
Containers
<span> <array> <vector>	<deque> <forward_list> <list>	<map> <set> <queue>	<unordered_map> <unordered_set> <stack>
Iterators
<iterator>
Algorithms
<algorithm>	<execution>
Numerics
<complex> <random>	<valarray> <numeric>	<cfenv> <cmath>	<bit>
Input/Output
<iosfwd> <ios> <iomanip> <streambuf>	<istream> <ostream> <iostream>	<sstream> <fstream> <syncstream>	<cstdio> <cinttypes> <strstream>
Regular expressions
<regex>
Filesystem support
<filesystem>
Thread support
<thread> <atomic>	<mutex> <shared_mutex>	<condition_variable> <future>
C compatibility
<ciso646> <cstdalign>	<cstdbool> <ccomplex>	<ctgmath>

This header is part of the containers library.

Includes
<initializer_list> (C++11)
Classes
unordered_set (C++11)	collection of unique keys, hashed by keys (class template)
unordered_multiset (C++11)	collection of keys, hashed by keys (class template)
Functions
operator==operator!=	compares the values in the unordered_set (function template)
std::swap(std::unordered_set) (C++11)	specializes the std::swap algorithm (function template)
operator==operator!=	compares the values in the unordered_multiset (function template)
std::swap(std::unordered_multiset) (C++11)	specializes the std::swap algorithm (function template)

Synopsis

#include <initializer_list>

namespace std {
    // class template unordered_set:
    template <class Key,
            class Hash = hash<Key>,
            class Pred = std::equal_to<Key>,
            class Alloc = std::allocator<Key> >
        class unordered_set;

    // class template unordered_multiset:
    template <class Key,
            class Hash = hash<Key>,
            class Pred = std::equal_to<Key>,
            class Alloc = std::allocator<Key> >
        class unordered_multiset;

    template <class Key, class Hash, class Pred, class Alloc>
        void swap(unordered_set<Key, Hash, Pred, Alloc>& x,
                unordered_set<Key, Hash, Pred, Alloc>& y);
    template <class Key, class Hash, class Pred, class Alloc>
        void swap(unordered_multiset<Key, Hash, Pred, Alloc>& x,
                unordered_multiset<Key, Hash, Pred, Alloc>& y);

    template <class Key, class Hash, class Pred, class Alloc>
        bool operator==(const unordered_set<Key, Hash, Pred, Alloc>& a,
                        const unordered_set<Key, Hash, Pred, Alloc>& b);
    template <class Key, class Hash, class Pred, class Alloc>
        bool operator!=(const unordered_set<Key, Hash, Pred, Alloc>& a,
                        const unordered_set<Key, Hash, Pred, Alloc>& b);
    template <class Key, class Hash, class Pred, class Alloc>
        bool operator==(const unordered_multiset<Key, Hash, Pred, Alloc>& a,
                        const unordered_multiset<Key, Hash, Pred, Alloc>& b);
    template <class Key, class Hash, class Pred, class Alloc>
        bool operator!=(const unordered_multiset<Key, Hash, Pred, Alloc>& a,
                        const unordered_multiset<Key, Hash, Pred, Alloc>& b);
} // namespace std

Class std::unordered_set

template <class Key,
    class Hash = hash<Key>,
    class Pred = std::equal_to<Key>,
    class Allocator = std::allocator<Key> >
class unordered_set
{
public:
    // types
    typedef Key                                         key_type;
    typedef Key                                         value_type;
    typedef Hash                                        hasher;
    typedef Pred                                        key_equal;
    typedef Allocator                                   allocator_type;
    typedef typename allocator_type::pointer            pointer;
    typedef typename allocator_type::const_pointer      const_pointer;
    typedef typename allocator_type::reference          reference;
    typedef typename allocator_type::const_reference    const_reference;
    typedef /*implementation-defined*/                  size_type;
    typedef /*implementation-defined*/                  difference_type;

    typedef /*implementation-defined*/                  iterator;
    typedef /*implementation-defined*/                  const_iterator;
    typedef /*implementation-defined*/                  local_iterator;
    typedef /*implementation-defined*/                  const_local_iterator;

    // construct/destroy/copy
    explicit unordered_set(size_type n = implementation-defined,
                           const hasher& hf = hasher(),
                           const key_equal& eql = key_equal(),
                           const allocator_type& a = allocator_type());
    template <class InputIterator>
    unordered_set(InputIterator f, InputIterator l,
                  size_type n = see below,
                  const hasher& hf = hasher(),
                  const key_equal& eql = key_equal(),
                  const allocator_type& a = allocator_type());
    unordered_set(const unordered_set&);
    unordered_set(unordered_set&&);
    explicit unordered_set(const Allocator&);
    unordered_set(const unordered_set&, const Allocator&);
    unordered_set(unordered_set&&, const Allocator&);
    unordered_set(initializer_list<value_type>,
                  size_type = see below,
                  const hasher& hf = hasher(),
                  const key_equal& eql = key_equal(),
                  const allocator_type& a = allocator_type());
    ~unordered_set();
    unordered_set& operator=(const unordered_set&);
    unordered_set& operator=(unordered_set&&);
    unordered_set& operator=(initializer_list<value_type>);
    allocator_type get_allocator() const noexcept;

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

    // iterators
    iterator       begin() noexcept;
    const_iterator begin() const noexcept;
    iterator       end() noexcept;
    const_iterator end() const noexcept;
    const_iterator cbegin() const noexcept;
    const_iterator cend() 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& obj);
    pair<iterator, bool> insert(value_type&& obj);
    iterator insert(const_iterator hint, const value_type& obj);
    iterator insert(const_iterator hint, value_type&& obj);
    template <class InputIterator> void insert(InputIterator first, InputIterator last);
    void insert(initializer_list<value_type>);

    iterator erase(const_iterator position);
    size_type erase(const key_type& k);
    iterator erase(const_iterator first, const_iterator last);
    void clear() noexcept;

    void swap(unordered_set&);

    // observers
    hasher hash_function() const;
    key_equal key_eq() const;

    // lookup
    iterator       find(const key_type& k);
    const_iterator find(const key_type& k) const;
    size_type count(const key_type& k) const;
    std::pair<iterator, iterator> equal_range(const key_type& k);
    std::pair<const_iterator, const_iterator> equal_range(const key_type& k) const;

    // bucket interface
    size_type bucket_count() const noexcept;
    size_type max_bucket_count() const noexcept;
    size_type bucket_size(size_type n) const;
    size_type bucket(const key_type& k) const;
    local_iterator begin(size_type n);
    const_local_iterator begin(size_type n) const;
    local_iterator end(size_type n);
    const_local_iterator end(size_type n) const;
    const_local_iterator cbegin(size_type n) const;
    const_local_iterator cend(size_type n) const;

    // hash policy
    float load_factor() const noexcept;
    float max_load_factor() const noexcept;
    void max_load_factor(float z);
    void rehash(size_type n);
    void reserve(size_type n);
};

Class std::unordered_multiset

template <class Key,
    class Hash = hash<Key>,
    class Pred = std::equal_to<Key>,
    class Allocator = std::allocator<Key> >
class unordered_multiset
{
public:
    // types
    typedef Key                                         key_type;
    typedef Key                                         value_type;
    typedef Hash                                        hasher;
    typedef Pred                                        key_equal;
    typedef Allocator                                   allocator_type;
    typedef typename allocator_type::pointer            pointer;
    typedef typename allocator_type::const_pointer      const_pointer;
    typedef typename allocator_type::reference          reference;
    typedef typename allocator_type::const_reference    const_reference;
    typedef /*implementation-defined*/                  size_type;
    typedef /*implementation-defined*/                  difference_type;
    typedef /*implementation-defined*/                  iterator;
    typedef /*implementation-defined*/                  const_iterator;
    typedef /*implementation-defined*/                  local_iterator;
    typedef /*implementation-defined*/                  const_local_iterator;

    // construct/destroy/copy
    explicit unordered_multiset(size_type n = /*implementation-defined*/,
                                const hasher& hf = hasher(),
                                const key_equal& eql = key_equal(),
                                const allocator_type& a = allocator_type());
    template <class InputIterator>
    unordered_multiset(InputIterator f, InputIterator l,
                       size_type n = see below,
                       const hasher& hf = hasher(),
                       const key_equal& eql = key_equal(),
                       const allocator_type& a = allocator_type());
    unordered_multiset(const unordered_multiset&);
    unordered_multiset(unordered_multiset&&);
    explicit unordered_multiset(const Allocator&);
    unordered_multiset(const unordered_multiset&, const Allocator&);
    unordered_multiset(unordered_multiset&&, const Allocator&);
    unordered_multiset(initializer_list<value_type>,
                       size_type = see below,
                       const hasher& hf = hasher(),
                       const key_equal& eql = key_equal(),
                       const allocator_type& a = allocator_type());
    ~unordered_multiset();
    unordered_multiset& operator=(const unordered_multiset&);
    unordered_multiset operator=(unordered_multiset&&);
    unordered_multiset& operator=(initializer_list<value_type>);
    allocator_type get_allocator() const noexcept;

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

    // iterators
    iterator       begin() noexcept;
    const_iterator begin() const noexcept;
    iterator       end() noexcept;
    const_iterator end() const noexcept;
    const_iterator cbegin() const noexcept;
    const_iterator cend() 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& obj);
    iterator insert(value_type&& obj);
    iterator insert(const_iterator hint, const value_type& obj);
    iterator insert(const_iterator hint, value_type&& obj);
    template <class InputIterator> void insert(InputIterator first, InputIterator last);
    void insert(initializer_list<value_type>);

    iterator erase(const_iterator position);
    size_type erase(const key_type& k);
    iterator erase(const_iterator first, const_iterator last);
    void clear() noexcept;

    void swap(unordered_multiset&);

    // observers
    hasher hash_function() const;
    key_equal key_eq() const;

    // lookup
    iterator        find(const key_type& k);
    const_iterator  find(const key_type& k) const;
    size_type count(const key_type& k) const;
    std::pair<iterator, iterator>             equal_range(const key_type& k);
    std::pair<const_iterator, const_iterator> equal_range(const key_type& k) const;

    // bucket interface
    size_type bucket_count() const noexcept;
    size_type max_bucket_count() const noexcept;
    size_type bucket_size(size_type n) const;
    size_type bucket(const key_type& k) const;
    local_iterator       begin(size_type n);
    const_local_iterator begin(size_type n) const;
    local_iterator       end(size_type n);
    const_local_iterator end(size_type n) const;
    const_local_iterator cbegin(size_type n) const;
    const_local_iterator cend(size_type n) const;

    // hash policy
    float load_factor() const noexcept;
    float max_load_factor() const noexcept;
    void max_load_factor(float z);
    void rehash(size_type n);
    void reserve(size_type n);
};