Standard library header <unordered_map> (C++11)

 

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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
unordered_map (C++11)	collection of key-value pairs, hashed by keys, keys are unique (class template)
unordered_multimap (C++11)	collection of key-value pairs, hashed by keys (class template)
Functions
operator==operator!= (C++11)(C++11)(removed in C++20)	compares the values in the unordered_map (function template)
std::swap(std::unordered_map) (C++11)	specializes the std::swap algorithm (function template)
erase_if(std::unordered_map) (C++20)	erases all elements satisfying specific criteria (function template)
operator==operator!= (C++11)(C++11)(removed in C++20)	compares the values in the unordered_multimap (function template)
std::swap(std::unordered_multimap) (C++11)	specializes the std::swap algorithm (function template)
erase_if(std::unordered_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 unordered_maptemplate<class Key, class T, class Hash = hash<Key>, class Pred = equal_to<Key>, class Alloc = allocator<pair<const Key, T>>>class unordered_map;   // class template unordered_multimaptemplate<class Key, class T, class Hash = hash<Key>, class Pred = equal_to<Key>, class Alloc = allocator<pair<const Key, T>>>class unordered_multimap;   template<class Key, class T, class Hash, class Pred, class Alloc>bool operator==(const unordered_map<Key, T, Hash, Pred, Alloc>& a, const unordered_map<Key, T, Hash, Pred, Alloc>& b);   template<class Key, class T, class Hash, class Pred, class Alloc>bool operator==(const unordered_multimap<Key, T, Hash, Pred, Alloc>& a, const unordered_multimap<Key, T, Hash, Pred, Alloc>& b);   template<class Key, class T, class Hash, class Pred, class Alloc>void swap(unordered_map<Key, T, Hash, Pred, Alloc>& x, unordered_map<Key, T, Hash, Pred, Alloc>& y)noexcept(noexcept(x.swap(y)));   template<class Key, class T, class Hash, class Pred, class Alloc>void swap( unordered_multimap<Key, T, Hash, Pred, Alloc>& x, unordered_multimap<Key, T, Hash, Pred, Alloc>& y)noexcept(noexcept(x.swap(y)));   // erasure for unordered_maptemplate<class K, class T, class H, class P, class A, class Predicate>typename unordered_map<K, T, H, P, A>::size_type erase_if( unordered_map<K, T, H, P, A>& c, Predicate pred);   // erasure for unordered_multimaptemplate<class K, class T, class H, class P, class A, class Predicate>typename unordered_multimap<K, T, H, P, A>::size_type erase_if( unordered_multimap<K, T, H, P, A>& c, Predicate pred);   namespace pmr {template<class Key, class T, class Hash = hash<Key>, class Pred = equal_to<Key>>using unordered_map =std::unordered_map<Key, T, Hash, Pred, polymorphic_allocator<pair<const Key, T>>>;template<class Key, class T, class Hash = hash<Key>, class Pred = equal_to<Key>>using unordered_multimap = std::unordered_multimap<Key, T, Hash, Pred, polymorphic_allocator<pair<const Key, T>>>;   }}

Class template std::unordered_map

namespace std {template<class Key, class T, class Hash = hash<Key>, class Pred = equal_to<Key>, class Allocator = allocator<pair<const Key, T>>>class unordered_map {public:// typesusing key_type = Key;using mapped_type = T;using value_type = pair<const Key, T>;using hasher = Hash;using key_equal = Pred;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 local_iterator =/* implementation-defined */;using const_local_iterator =/* implementation-defined */;using node_type =/* unspecified */;using insert_return_type =/*insert-return-type*/<iterator, node_type>;   // construct/copy/destroy unordered_map();explicit unordered_map(size_type n, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type());template<class InputIter> unordered_map(InputIter f, InputIter l, size_type n =/* see description */, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type());   template<container-compatible-range<value_type> R> unordered_map(from_range_t, R&& rg, size_type n =/* see description */, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); unordered_map(const unordered_map&); unordered_map(unordered_map&&);explicit unordered_map(const Allocator&); unordered_map(const unordered_map&, const type_identity_t<Allocator>&); unordered_map(unordered_map&&, const type_identity_t<Allocator>&); unordered_map(initializer_list<value_type> il, size_type n =/* see description */, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); unordered_map(size_type n, const allocator_type& a): unordered_map(n, hasher(), key_equal(), a){} unordered_map(size_type n, const hasher& hf, const allocator_type& a): unordered_map(n, hf, key_equal(), a){}template<class InputIter> unordered_map(InputIter f, InputIter l, size_type n, const allocator_type& a): unordered_map(f, l, n, hasher(), key_equal(), a){}template<class InputIter> unordered_map(InputIter f, InputIter l, size_type n, const hasher& hf, const allocator_type& a): unordered_map(f, l, n, hf, key_equal(), a){}template<container-compatible-range<value_type> R> unordered_map(from_range_t, R&& rg, size_type n, const allocator_type& a): unordered_map(from_range, std::forward<R>(rg), n, hasher(), key_equal(), a){}template<container-compatible-range<value_type> R> unordered_map(from_range_t, R&& rg, size_type n, const hasher& hf, const allocator_type& a): unordered_map(from_range, std::forward<R>(rg), n, hf, key_equal(), a){} unordered_map(initializer_list<value_type> il, size_type n, const allocator_type& a): unordered_map(il, n, hasher(), key_equal(), a){} unordered_map(initializer_list<value_type> il, size_type n, const hasher& hf, const allocator_type& a): unordered_map(il, n, hf, key_equal(), a){} ~unordered_map(); unordered_map& operator=(const unordered_map&); unordered_map& operator=(unordered_map&&)noexcept( allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_move_assignable_v<Hash>&& is_nothrow_move_assignable_v<Pred>); unordered_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; const_iterator cbegin()constnoexcept; const_iterator cend()constnoexcept;   // capacitybool empty()constnoexcept; size_type size()constnoexcept; size_type max_size()constnoexcept;   // 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& obj); pair<iterator, bool> insert(value_type&& obj);template<class P> pair<iterator, bool> insert(P&& obj); iterator insert(const_iterator hint, const value_type& obj); iterator insert(const_iterator hint, value_type&& obj);template<class P> iterator insert(const_iterator hint, P&& obj);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& k);template<class K> size_type erase(K&& x); iterator erase(const_iterator first, const_iterator last);void swap(unordered_map&)noexcept( allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_swappable_v<Hash>&& is_nothrow_swappable_v<Pred>);void clear()noexcept;   template<class H2, class P2>void merge(unordered_map<Key, T, H2, P2, Allocator>& source);template<class H2, class P2>void merge(unordered_map<Key, T, H2, P2, Allocator>&& source);template<class H2, class P2>void merge(unordered_multimap<Key, T, H2, P2, Allocator>& source);template<class H2, class P2>void merge(unordered_multimap<Key, T, H2, P2, Allocator>&& source);   // observers hasher hash_function()const; key_equal key_eq()const;   // map operations iterator find(const key_type& k); const_iterator find(const key_type& k)const;template<class K> iterator find(const K& k);template<class K> const_iterator find(const K& k)const; size_type count(const key_type& k)const;template<class K> size_type count(const K& k)const;bool contains(const key_type& k)const;template<class K>bool contains(const K& k)const; pair<iterator, iterator> equal_range(const key_type& k); pair<const_iterator, const_iterator> equal_range(const key_type& k)const;template<class K> pair<iterator, iterator> equal_range(const K& k);template<class K> pair<const_iterator, const_iterator> equal_range(const K& k)const;   // element access mapped_type& operator[](const key_type& k); mapped_type& operator[](key_type&& k);template<class K> mapped_type& operator[](K&& k); mapped_type& at(const key_type& k);const mapped_type& at(const key_type& k)const;template<class K> mapped_type& at(const K& k);template<class K>const mapped_type& at(const K& k)const;   // bucket interface size_type bucket_count()constnoexcept; size_type max_bucket_count()constnoexcept; size_type bucket_size(size_type n)const; size_type bucket(const key_type& k)const;template<class K> size_type bucket(const K& 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 policyfloat load_factor()constnoexcept;float max_load_factor()constnoexcept;void max_load_factor(float z);void rehash(size_type n);void reserve(size_type n);};   template<class InputIter, class Hash = hash</*iter-key-type*/<InputIter>>, class Pred = equal_to</*iter-key-type*/<InputIter>>, class Allocator = allocator</*iter-to-alloc-type*/<InputIter>>> unordered_map(InputIter, InputIter, typename/* see description */::size_type=/* see description */, Hash = Hash(), Pred = Pred(), Allocator = Allocator())-> unordered_map</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, Hash, Pred, Allocator>;   template<ranges::input_range R, class Hash = hash</*range-key-type*/<R>>, class Pred = equal_to</*range-key-type*/<R>>, class Allocator = allocator</*range-to-alloc-type*/<R>>> unordered_map(from_range_t, R&&, typename/* see description */::size_type=/* see description */, Hash = Hash(), Pred = Pred(), Allocator = Allocator())-> unordered_map</*range-key-type*/<R>, /*range-mapped-type*/<R>, Hash, Pred, Allocator>;   template<class Key, class T, class Hash = hash<Key>, class Pred = equal_to<Key>, class Allocator = allocator<pair<const Key, T>>> unordered_map(initializer_list<pair<Key, T>>, typename/* see description */::size_type=/* see description */, Hash = Hash(), Pred = Pred(), Allocator = Allocator())-> unordered_map<Key, T, Hash, Pred, Allocator>;   template<class InputIter, class Allocator> unordered_map(InputIter, InputIter, typename/* see description */::size_type, Allocator)-> unordered_map</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, hash</*iter-key-type*/<InputIter>>, equal_to</*iter-key-type*/<InputIter>>, Allocator>;   template<class InputIter, class Allocator> unordered_map(InputIter, InputIter, Allocator)-> unordered_map</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, hash</*iter-key-type*/<InputIter>>, equal_to</*iter-key-type*/<InputIter>>, Allocator>;   template<class InputIter, class Hash, class Allocator> unordered_map(InputIter, InputIter, typename/* see description */::size_type, Hash, Allocator)-> unordered_map</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, Hash, equal_to</*iter-key-type*/<InputIter>>, Allocator>;   template<ranges::input_range R, class Allocator> unordered_map(from_range_t, R&&, typename/* see description */::size_type, Allocator)-> unordered_map</*range-key-type*/<R>, /*range-mapped-type*/<R>, hash</*range-key-type*/<R>>, equal_to</*range-key-type*/<R>>, Allocator>;   template<ranges::input_range R, class Allocator> unordered_map(from_range_t, R&&, Allocator)-> unordered_map</*range-key-type*/<R>, /*range-mapped-type*/<R>, hash</*range-key-type*/<R>>, equal_to</*range-key-type*/<R>>, Allocator>;   template<ranges::input_range R, class Hash, class Allocator> unordered_map(from_range_t, R&&, typename/* see description */::size_type, Hash, Allocator)-> unordered_map</*range-key-type*/<R>, /*range-mapped-type*/<R>, Hash, equal_to</*range-key-type*/<R>>, Allocator>;   template<class Key, class T, class Allocator> unordered_map(initializer_list<pair<Key, T>>, typename/* see description */::size_type, Allocator)-> unordered_map<Key, T, hash<Key>, equal_to<Key>, Allocator>;   template<class Key, class T, class Allocator> unordered_map(initializer_list<pair<Key, T>>, Allocator)-> unordered_map<Key, T, hash<Key>, equal_to<Key>, Allocator>;   template<class Key, class T, class Hash, class Allocator> unordered_map(initializer_list<pair<Key, T>>, typename/* see description */::size_type, Hash, Allocator)-> unordered_map<Key, T, Hash, equal_to<Key>, Allocator>;}

Class template std::unordered_multimap

namespace std {template<class Key, class T, class Hash = hash<Key>, class Pred = equal_to<Key>, class Allocator = allocator<pair<const Key, T>>>class unordered_multimap {public:// typesusing key_type = Key;using mapped_type = T;using value_type = pair<const Key, T>;using hasher = Hash;using key_equal = Pred;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 local_iterator =/* implementation-defined */;using const_local_iterator =/* implementation-defined */;using node_type =/* unspecified */;   // construct/copy/destroy unordered_multimap();explicit unordered_multimap(size_type n, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type());template<class InputIter> unordered_multimap(InputIter f, InputIter l, size_type n =/* see description */, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type());template<container-compatible-range<value_type> R> unordered_multimap(from_range_t, R&& rg, size_type n =/* see description */, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); unordered_multimap(const unordered_multimap&); unordered_multimap(unordered_multimap&&);explicit unordered_multimap(const Allocator&); unordered_multimap(const unordered_multimap&, const type_identity_t<Allocator>&); unordered_multimap(unordered_multimap&&, const type_identity_t<Allocator>&); unordered_multimap(initializer_list<value_type> il, size_type n =/* see description */, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); unordered_multimap(size_type n, const allocator_type& a): unordered_multimap(n, hasher(), key_equal(), a){} unordered_multimap(size_type n, const hasher& hf, const allocator_type& a): unordered_multimap(n, hf, key_equal(), a){}template<class InputIter> unordered_multimap(InputIter f, InputIter l, size_type n, const allocator_type& a): unordered_multimap(f, l, n, hasher(), key_equal(), a){}template<class InputIter> unordered_multimap(InputIter f, InputIter l, size_type n, const hasher& hf, const allocator_type& a): unordered_multimap(f, l, n, hf, key_equal(), a){}template<container-compatible-range<value_type> R> unordered_multimap(from_range_t, R&& rg, size_type n, const allocator_type& a): unordered_multimap(from_range, std::forward<R>(rg), n, hasher(), key_equal(), a){}template<container-compatible-range<value_type> R> unordered_multimap(from_range_t, R&& rg, size_type n, const hasher& hf, const allocator_type& a): unordered_multimap(from_range, std::forward<R>(rg), n, hf, key_equal(), a){} unordered_multimap(initializer_list<value_type> il, size_type n, const allocator_type& a): unordered_multimap(il, n, hasher(), key_equal(), a){} unordered_multimap(initializer_list<value_type> il, size_type n, const hasher& hf, const allocator_type& a): unordered_multimap(il, n, hf, key_equal(), a){} ~unordered_multimap(); unordered_multimap& operator=(const unordered_multimap&); unordered_multimap& operator=(unordered_multimap&&)noexcept( allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_move_assignable_v<Hash>&& is_nothrow_move_assignable_v<Pred>); unordered_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; const_iterator cbegin()constnoexcept; const_iterator cend()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& obj); iterator insert(value_type&& obj);template<class P> iterator insert(P&& obj); iterator insert(const_iterator hint, const value_type& obj); iterator insert(const_iterator hint, value_type&& obj);template<class P> iterator insert(const_iterator hint, P&& obj);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& k);template<class K> size_type erase(K&& x); iterator erase(const_iterator first, const_iterator last);void swap(unordered_multimap&)noexcept( allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_swappable_v<Hash>&& is_nothrow_swappable_v<Pred>);void clear()noexcept;   template<class H2, class P2>void merge(unordered_multimap<Key, T, H2, P2, Allocator>& source);template<class H2, class P2>void merge(unordered_multimap<Key, T, H2, P2, Allocator>&& source);template<class H2, class P2>void merge(unordered_map<Key, T, H2, P2, Allocator>& source);template<class H2, class P2>void merge(unordered_map<Key, T, H2, P2, Allocator>&& source);   // observers hasher hash_function()const; key_equal key_eq()const;   // map operations iterator find(const key_type& k); const_iterator find(const key_type& k)const;template<class K> iterator find(const K& k);template<class K> const_iterator find(const K& k)const; size_type count(const key_type& k)const;template<class K> size_type count(const K& k)const;bool contains(const key_type& k)const;template<class K>bool contains(const K& k)const; pair<iterator, iterator> equal_range(const key_type& k); pair<const_iterator, const_iterator> equal_range(const key_type& k)const;template<class K> pair<iterator, iterator> equal_range(const K& k);template<class K> pair<const_iterator, const_iterator> equal_range(const K& k)const;   // bucket interface size_type bucket_count()constnoexcept; size_type max_bucket_count()constnoexcept; size_type bucket_size(size_type n)const; size_type bucket(const key_type& k)const;template<class K> size_type bucket(const K& 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 policyfloat load_factor()constnoexcept;float max_load_factor()constnoexcept;void max_load_factor(float z);void rehash(size_type n);void reserve(size_type n);};   template<class InputIter, class Hash = hash</*iter-key-type*/<InputIter>>, class Pred = equal_to</*iter-key-type*/<InputIter>>, class Allocator = allocator</*iter-to-alloc-type*/<InputIter>>> unordered_multimap(InputIter, InputIter, typename/* see description */::size_type=/* see description */, Hash = Hash(), Pred = Pred(), Allocator = Allocator())-> unordered_multimap</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, Hash, Pred, Allocator>;   template<ranges::input_range R, class Hash = hash</*range-key-type*/<R>>, class Pred = equal_to</*range-key-type*/<R>>, class Allocator = allocator</*range-to-alloc-type*/<R>>> unordered_multimap(from_range_t, R&&, typename/* see description */::size_type=/* see description */, Hash = Hash(), Pred = Pred(), Allocator = Allocator())-> unordered_multimap</*range-key-type*/<R>, /*range-mapped-type*/<R>, Hash, Pred, Allocator>;   template<class Key, class T, class Hash = hash<Key>, class Pred = equal_to<Key>, class Allocator = allocator<pair<const Key, T>>> unordered_multimap(initializer_list<pair<Key, T>>, typename/* see description */::size_type=/* see description */, Hash = Hash(), Pred = Pred(), Allocator = Allocator())-> unordered_multimap<Key, T, Hash, Pred, Allocator>;   template<class InputIter, class Allocator> unordered_multimap(InputIter, InputIter, typename/* see description */::size_type, Allocator)-> unordered_multimap</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, hash</*iter-key-type*/<InputIter>>, equal_to</*iter-key-type*/<InputIter>>, Allocator>;   template<class InputIter, class Allocator> unordered_multimap(InputIter, InputIter, Allocator)-> unordered_multimap</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, hash</*iter-key-type*/<InputIter>>, equal_to</*iter-key-type*/<InputIter>>, Allocator>;   template<class InputIter, class Hash, class Allocator> unordered_multimap(InputIter, InputIter, typename/* see description */::size_type, Hash, Allocator)-> unordered_multimap</*iter-key-type*/<InputIter>, /*iter-mapped-type*/<InputIter>, Hash, equal_to</*iter-key-type*/<InputIter>>, Allocator>;   template<ranges::input_range R, class Allocator> unordered_multimap(from_range_t, R&&, typename/* see description */::size_type, Allocator)-> unordered_multimap</*range-key-type*/<R>, /*range-mapped-type*/<R>, hash</*range-key-type*/<R>>, equal_to</*range-key-type*/<R>>, Allocator>;   template<ranges::input_range R, class Allocator> unordered_multimap(from_range_t, R&&, Allocator)-> unordered_multimap</*range-key-type*/<R>, /*range-mapped-type*/<R>, hash</*range-key-type*/<R>>, equal_to</*range-key-type*/<R>>, Allocator>;   template<ranges::input_range R, class Hash, class Allocator> unordered_multimap(from_range_t, R&&, typename/* see description */::size_type, Hash, Allocator)-> unordered_multimap</*range-key-type*/<R>, /*range-mapped-type*/<R>, Hash, equal_to</*range-key-type*/<R>>, Allocator>;   template<class Key, class T, class Allocator> unordered_multimap(initializer_list<pair<Key, T>>, typename/* see description */::size_type, Allocator)-> unordered_multimap<Key, T, hash<Key>, equal_to<Key>, Allocator>;   template<class Key, class T, class Allocator> unordered_multimap(initializer_list<pair<Key, T>>, Allocator)-> unordered_multimap<Key, T, hash<Key>, equal_to<Key>, Allocator>;   template<class Key, class T, class Hash, class Allocator> unordered_multimap(initializer_list<pair<Key, T>>, typename/* see description */::size_type, Hash, Allocator)-> unordered_multimap<Key, T, Hash, equal_to<Key>, Allocator>;}