An unordered_multiset is an unordered associative container that supports equivalent keys (an instance of unordered_multiset may contain multiple copies of the same key value) and in which each element's key is the element itself. The unordered_multiset class supports forward iterators.
An unordered_multiset satisfies all of the requirements of a container, of an unordered associative container, and of an allocator-aware container. It provides the operations described in the preceding requirements table for equivalent keys; that is, an unordered_multiset supports the a_eq operations in that table, not the a_uniq operations. For an unordered_multiset<Key> the key type and the value type are both Key. The iterator and const_iterator types are both constant iterator types. It is unspecified whether they are the same type.
This section only describes operations on unordered_multiset that are not described in one of the requirement tables, or for which there is additional semantic information.
namespace std { template <class Key, class Hash = hash<Key>, class Pred = equal_to<Key>, class Allocator = allocator<Key>> class unordered_multiset { public: // types: using key_type = Key; using value_type = Key; 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; // see [container.requirements] using difference_type = implementation-defined; // see [container.requirements] using iterator = implementation-defined; // see [container.requirements] using const_iterator = implementation-defined; // see [container.requirements] using local_iterator = implementation-defined; // see [container.requirements] using const_local_iterator = implementation-defined; // see [container.requirements] using node_type = unspecified; // [unord.multiset.cnstr], construct/copy/destroy unordered_multiset(); explicit unordered_multiset(size_type n, 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> il, size_type n = see below, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); unordered_multiset(size_type n, const allocator_type& a) : unordered_multiset(n, hasher(), key_equal(), a) { } unordered_multiset(size_type n, const hasher& hf, const allocator_type& a) : unordered_multiset(n, hf, key_equal(), a) { } template <class InputIterator> unordered_multiset(InputIterator f, InputIterator l, size_type n, const allocator_type& a) : unordered_multiset(f, l, n, hasher(), key_equal(), a) { } template <class InputIterator> unordered_multiset(InputIterator f, InputIterator l, size_type n, const hasher& hf, const allocator_type& a) : unordered_multiset(f, l, n, hf, key_equal(), a) { } unordered_multiset(initializer_list<value_type> il, size_type n, const allocator_type& a) : unordered_multiset(il, n, hasher(), key_equal(), a) { } unordered_multiset(initializer_list<value_type> il, size_type n, const hasher& hf, const allocator_type& a) : unordered_multiset(il, n, hf, key_equal(), a) { } ~unordered_multiset(); unordered_multiset& operator=(const unordered_multiset&); unordered_multiset& operator=(unordered_multiset&&) noexcept(allocator_traits<Allocator>::is_always_equal::value && is_nothrow_move_assignable_v<Hash> && is_nothrow_move_assignable_v<Pred>); unordered_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; const_iterator cbegin() const noexcept; const_iterator cend() 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& 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>); node_type extract(const_iterator position); node_type extract(const key_type& 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); iterator erase(const_iterator first, const_iterator last); void swap(unordered_multiset&) 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_multiset<Key, H2, P2, Allocator>& source); template<class H2, class P2> void merge(unordered_multiset<Key, H2, P2, Allocator>&& source); template<class H2, class P2> void merge(unordered_set<Key, H2, P2, Allocator>& source); template<class H2, class P2> void merge(unordered_set<Key, H2, P2, Allocator>&& source); // observers: hasher hash_function() const; key_equal key_eq() const; // set operations: iterator find(const key_type& k); const_iterator find(const key_type& k) const; size_type count(const key_type& k) const; pair<iterator, iterator> equal_range(const key_type& k); 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); }; template<class InputIterator, class Hash = hash<typename iterator_traits<InputIterator>::value_type>, class Pred = equal_to<typename iterator_traits<InputIterator>::value_type>, class Allocator = allocator<typename iterator_traits<InputIterator>::value_type>> unordered_multiset(InputIterator, InputIterator, see below::size_type = see below, Hash = Hash(), Pred = Pred(), Allocator = Allocator()) -> unordered_multiset<typename iterator_traits<InputIterator>::value_type, Hash, Pred, Allocator>; template<class T, class Hash = hash<T>, class Pred = equal_to<T>, class Allocator = allocator<T>> unordered_multiset(initializer_list<T>, typename see below::size_type = see below, Hash = Hash(), Pred = Pred(), Allocator = Allocator()) -> unordered_multiset<T, Hash, Pred, Allocator>; template<class InputIterator, class Allocator> unordered_multiset(InputIterator, InputIterator, typename see below::size_type, Allocator) -> unordered_multiset<typename iterator_traits<InputIterator>::value_type, hash<typename iterator_traits<InputIterator>::value_type>, equal_to<typename iterator_traits<InputIterator>::value_type>, Allocator>; template<class InputIterator, class Hash, class Allocator> unordered_multiset(InputIterator, InputIterator, typename see below::size_type, Hash, Allocator) -> unordered_multiset<typename iterator_traits<InputIterator>::value_type, Hash, equal_to<typename iterator_traits<InputIterator>::value_type>, Allocator>; template<class T, class Allocator> unordered_multiset(initializer_list<T>, typename see below::size_type, Allocator) -> unordered_multiset<T, hash<T>, equal_to<T>, Allocator>; template<class T, class Hash, class Allocator> unordered_multiset(initializer_list<T>, typename see below::size_type, Hash, Allocator) -> unordered_multiset<T, Hash, equal_to<T>, Allocator>; 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); // [unord.multiset.swap], swap 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) noexcept(noexcept(x.swap(y))); }