A multimap is an associative container that supports equivalent keys (possibly containing multiple copies of the same key value) and provides for fast retrieval of values of another type T based on the keys. The multimap class supports bidirectional iterators.
A multimap satisfies all of the requirements of a container and of a reversible container, of an associative container, and of an allocator-aware container. A multimap also provides most operations described in [associative.reqmts] for equal keys. This means that a multimap supports the a_eq operations in [associative.reqmts] but not the a_uniq operations. For a multimap<Key,T> the key_type is Key and the value_type is pair<const Key,T>. Descriptions are provided here only for operations on multimap that are not described in one of those tables or for operations where there is additional semantic information.
namespace std { template <class Key, class T, class Compare = less<Key>, class Allocator = allocator<pair<const Key, T>>> class multimap { public: // types: using key_type = Key; using mapped_type = T; using value_type = pair<const Key, T>; using key_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; // 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 reverse_iterator = std::reverse_iterator<iterator>; using const_reverse_iterator = std::reverse_iterator<const_iterator>; using node_type = unspecified; class value_compare { friend class multimap; protected: Compare comp; value_compare(Compare c) : comp(c) { } public: bool operator()(const value_type& x, const value_type& y) const { return comp(x.first, y.first); } }; // [multimap.cons], construct/copy/destroy multimap() : multimap(Compare()) { } explicit multimap(const Compare& comp, const Allocator& = Allocator()); template <class InputIterator> multimap(InputIterator first, InputIterator last, const Compare& comp = Compare(), const Allocator& = Allocator()); multimap(const multimap& x); multimap(multimap&& x); explicit multimap(const Allocator&); multimap(const multimap&, const Allocator&); multimap(multimap&&, const Allocator&); multimap(initializer_list<value_type>, const Compare& = Compare(), const Allocator& = Allocator()); template <class InputIterator> multimap(InputIterator first, InputIterator last, const Allocator& a) : multimap(first, last, Compare(), a) { } multimap(initializer_list<value_type> il, const Allocator& a) : multimap(il, Compare(), a) { } ~multimap(); multimap& operator=(const multimap& x); multimap& operator=(multimap&& x) noexcept(allocator_traits<Allocator>::is_always_equal::value && is_nothrow_move_assignable_v<Compare>); multimap& 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; // [multimap.modifiers], 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); template <class P> iterator insert(P&& x); iterator insert(const_iterator position, const value_type& x); iterator insert(const_iterator position, value_type&& x); template <class P> iterator insert(const_iterator position, P&& x); 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& x); iterator erase(const_iterator first, const_iterator last); void swap(multimap&) noexcept(allocator_traits<Allocator>::is_always_equal::value && is_nothrow_swappable_v<Compare>); void clear() noexcept; template<class C2> void merge(multimap<Key, T, C2, Allocator>& source); template<class C2> void merge(multimap<Key, T, C2, Allocator>&& source); template<class C2> void merge(map<Key, T, C2, Allocator>& source); template<class C2> void merge(map<Key, T, C2, Allocator>&& source); // observers: key_compare key_comp() const; value_compare value_comp() const; // map 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; 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 InputIterator, class Compare = less<iter_key_t<InputIterator>>, class Allocator = allocator<iter_to_alloc_t<InputIterator>>> multimap(InputIterator, InputIterator, Compare = Compare(), Allocator = Allocator()) -> multimap<iter_key_t<InputIterator>, iter_val_t<InputIterator>, Compare, Allocator>; template<class Key, class T, class Compare = less<Key>, class Allocator = allocator<pair<const Key, T>>> multimap(initializer_list<pair<const Key, T>>, Compare = Compare(), Allocator = Allocator()) -> multimap<Key, T, Compare, Allocator>; template<class InputIterator, class Allocator> multimap(InputIterator, InputIterator, Allocator) -> multimap<iter_key_t<InputIterator>, iter_val_t<InputIterator>, less<iter_key_t<InputIterator>>, Allocator>; template<class Key, class T, class Allocator> multimap(initializer_list<pair<const Key, T>>, Allocator) -> multimap<Key, T, less<Key>, Allocator>; template <class Key, class T, class Compare, class Allocator> bool operator==(const multimap<Key, T, Compare, Allocator>& x, const multimap<Key, T, Compare, Allocator>& y); template <class Key, class T, class Compare, class Allocator> bool operator< (const multimap<Key, T, Compare, Allocator>& x, const multimap<Key, T, Compare, Allocator>& y); template <class Key, class T, class Compare, class Allocator> bool operator!=(const multimap<Key, T, Compare, Allocator>& x, const multimap<Key, T, Compare, Allocator>& y); template <class Key, class T, class Compare, class Allocator> bool operator> (const multimap<Key, T, Compare, Allocator>& x, const multimap<Key, T, Compare, Allocator>& y); template <class Key, class T, class Compare, class Allocator> bool operator>=(const multimap<Key, T, Compare, Allocator>& x, const multimap<Key, T, Compare, Allocator>& y); template <class Key, class T, class Compare, class Allocator> bool operator<=(const multimap<Key, T, Compare, Allocator>& x, const multimap<Key, T, Compare, Allocator>& y); // [multimap.special], specialized algorithms template <class Key, class T, class Compare, class Allocator> void swap(multimap<Key, T, Compare, Allocator>& x, multimap<Key, T, Compare, Allocator>& y) noexcept(noexcept(x.swap(y))); }
explicit multimap(const Compare& comp, const Allocator& = Allocator());
template <class InputIterator>
multimap(InputIterator first, InputIterator last,
const Compare& comp = Compare(),
const Allocator& = Allocator());
Effects: Constructs an empty multimap using the specified comparison object and allocator, and inserts elements from the range [first, last).
template <class P> iterator insert(P&& x);
template <class P> iterator insert(const_iterator position, P&& x);
Effects: The first form is equivalent to return emplace(std::forward<P>(x)). The second form is equivalent to return emplace_hint(position, std::forward<P>(x)).
template <class Key, class T, class Compare, class Allocator>
void swap(multimap<Key, T, Compare, Allocator>& x,
multimap<Key, T, Compare, Allocator>& y)
noexcept(noexcept(x.swap(y)));