23 Containers library [containers]

23.4 Associative containers [associative]

23.4.3 Class template map [map]

23.4.3.1 Overview [map.overview]

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A map is an associative container that supports unique keys (i.e., contains at most one of each key value) and provides for fast retrieval of values of another type T based on the keys.
The map class supports bidirectional iterators.
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A map meets all of the requirements of a container ([container.reqmts]), of a reversible container ([container.rev.reqmts]), of an allocator-aware container ([container.alloc.reqmts]), and of an associative container ([associative.reqmts]).
A map also provides most operations described in [associative.reqmts] for unique keys.
This means that a map supports the a_uniq operations in [associative.reqmts] but not the a_eq operations.
For a map<Key,T> the key_type is Key and the value_type is pair<const Key,T>.
Descriptions are provided here only for operations on map that are not described in one of those tables or for operations where there is additional semantic information.
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The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
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namespace std { template<class Key, class T, class Compare = less<Key>, class Allocator = allocator<pair<const Key, T>>> class map { 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; using insert_return_type = insert-return-type<iterator, node_type>; class value_compare { protected: Compare comp; constexpr value_compare(Compare c) : comp(c) {} public: constexpr bool operator()(const value_type& x, const value_type& y) const { return comp(x.first, y.first); } }; // [map.cons], construct/copy/destroy constexpr map() : map(Compare()) { } constexpr explicit map(const Compare& comp, const Allocator& = Allocator()); template<class InputIterator> constexpr map(InputIterator first, InputIterator last, const Compare& comp = Compare(), const Allocator& = Allocator()); template<container-compatible-range<value_type> R> constexpr map(from_range_t, R&& rg, const Compare& comp = Compare(), const Allocator& = Allocator()); constexpr map(const map& x); constexpr map(map&& x); explicit map(const Allocator&); constexpr map(const map&, const type_identity_t<Allocator>&); constexpr map(map&&, const type_identity_t<Allocator>&); constexpr map(initializer_list<value_type>, const Compare& = Compare(), const Allocator& = Allocator()); template<class InputIterator> constexpr map(InputIterator first, InputIterator last, const Allocator& a) : map(first, last, Compare(), a) { } template<container-compatible-range<value_type> R> constexpr map(from_range_t, R&& rg, const Allocator& a)) : map(from_range, std::forward<R>(rg), Compare(), a) { } constexpr map(initializer_list<value_type> il, const Allocator& a) : map(il, Compare(), a) { } constexpr ~map(); constexpr map& operator=(const map& x); constexpr map& operator=(map&& x) noexcept(allocator_traits<Allocator>::is_always_equal::value && is_nothrow_move_assignable_v<Compare>); constexpr map& operator=(initializer_list<value_type>); constexpr allocator_type get_allocator() const noexcept; // iterators constexpr iterator begin() noexcept; constexpr const_iterator begin() const noexcept; constexpr iterator end() noexcept; constexpr const_iterator end() const noexcept; constexpr reverse_iterator rbegin() noexcept; constexpr const_reverse_iterator rbegin() const noexcept; constexpr reverse_iterator rend() noexcept; constexpr const_reverse_iterator rend() const noexcept; constexpr const_iterator cbegin() const noexcept; constexpr const_iterator cend() const noexcept; constexpr const_reverse_iterator crbegin() const noexcept; constexpr const_reverse_iterator crend() const noexcept; // capacity constexpr bool empty() const noexcept; constexpr size_type size() const noexcept; constexpr size_type max_size() const noexcept; // [map.access], element access constexpr mapped_type& operator[](const key_type& x); constexpr mapped_type& operator[](key_type&& x); template<class K> constexpr mapped_type& operator[](K&& x); constexpr mapped_type& at(const key_type& x); constexpr const mapped_type& at(const key_type& x) const; template<class K> constexpr mapped_type& at(const K& x); template<class K> constexpr const mapped_type& at(const K& x) const; // [map.modifiers], modifiers template<class... Args> constexpr pair<iterator, bool> emplace(Args&&... args); template<class... Args> constexpr iterator emplace_hint(const_iterator position, Args&&... args); constexpr pair<iterator, bool> insert(const value_type& x); constexpr pair<iterator, bool> insert(value_type&& x); template<class P> constexpr pair<iterator, bool> insert(P&& x); constexpr iterator insert(const_iterator position, const value_type& x); constexpr iterator insert(const_iterator position, value_type&& x); template<class P> constexpr iterator insert(const_iterator position, P&&); template<class InputIterator> constexpr void insert(InputIterator first, InputIterator last); template<container-compatible-range<value_type> R> constexpr void insert_range(R&& rg); constexpr void insert(initializer_list<value_type>); constexpr node_type extract(const_iterator position); constexpr node_type extract(const key_type& x); template<class K> constexpr node_type extract(K&& x); constexpr insert_return_type insert(node_type&& nh); constexpr iterator insert(const_iterator hint, node_type&& nh); template<class... Args> constexpr pair<iterator, bool> try_emplace(const key_type& k, Args&&... args); template<class... Args> constexpr pair<iterator, bool> try_emplace(key_type&& k, Args&&... args); template<class K, class... Args> constexpr pair<iterator, bool> try_emplace(K&& k, Args&&... args); template<class... Args> constexpr iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args); template<class... Args> constexpr iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args); template<class K, class... Args> constexpr iterator try_emplace(const_iterator hint, K&& k, Args&&... args); template<class M> constexpr pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj); template<class M> constexpr pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj); template<class K, class M> constexpr pair<iterator, bool> insert_or_assign(K&& k, M&& obj); template<class M> constexpr iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj); template<class M> constexpr iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj); template<class K, class M> constexpr iterator insert_or_assign(const_iterator hint, K&& k, M&& obj); constexpr iterator erase(iterator position); constexpr iterator erase(const_iterator position); constexpr size_type erase(const key_type& x); template<class K> constexpr size_type erase(K&& x); constexpr iterator erase(const_iterator first, const_iterator last); constexpr void swap(map&) noexcept(allocator_traits<Allocator>::is_always_equal::value && is_nothrow_swappable_v<Compare>); constexpr void clear() noexcept; template<class C2> constexpr void merge(map<Key, T, C2, Allocator>& source); template<class C2> constexpr void merge(map<Key, T, C2, Allocator>&& source); template<class C2> constexpr void merge(multimap<Key, T, C2, Allocator>& source); template<class C2> constexpr void merge(multimap<Key, T, C2, Allocator>&& source); // observers constexpr key_compare key_comp() const; constexpr value_compare value_comp() const; // map operations constexpr iterator find(const key_type& x); constexpr const_iterator find(const key_type& x) const; template<class K> constexpr iterator find(const K& x); template<class K> constexpr const_iterator find(const K& x) const; constexpr size_type count(const key_type& x) const; template<class K> constexpr size_type count(const K& x) const; constexpr bool contains(const key_type& x) const; template<class K> constexpr bool contains(const K& x) const; constexpr iterator lower_bound(const key_type& x); constexpr const_iterator lower_bound(const key_type& x) const; template<class K> constexpr iterator lower_bound(const K& x); template<class K> constexpr const_iterator lower_bound(const K& x) const; constexpr iterator upper_bound(const key_type& x); constexpr const_iterator upper_bound(const key_type& x) const; template<class K> constexpr iterator upper_bound(const K& x); template<class K> constexpr const_iterator upper_bound(const K& x) const; constexpr pair<iterator, iterator> equal_range(const key_type& x); constexpr pair<const_iterator, const_iterator> equal_range(const key_type& x) const; template<class K> constexpr pair<iterator, iterator> equal_range(const K& x); template<class K> constexpr pair<const_iterator, const_iterator> equal_range(const K& x) const; }; template<class InputIterator, class Compare = less<iter-key-type<InputIterator>>, class Allocator = allocator<iter-to-alloc-type<InputIterator>>> map(InputIterator, InputIterator, Compare = Compare(), Allocator = Allocator()) -> map<iter-key-type<InputIterator>, iter-mapped-type<InputIterator>, Compare, Allocator>; template<ranges::input_range R, class Compare = less<range-key-type<R>, class Allocator = allocator<range-to-alloc-type<R>>> map(from_range_t, R&&, Compare = Compare(), Allocator = Allocator()) -> map<range-key-type<R>, range-mapped-type<R>, Compare, Allocator>; template<class Key, class T, class Compare = less<Key>, class Allocator = allocator<pair<const Key, T>>> map(initializer_list<pair<Key, T>>, Compare = Compare(), Allocator = Allocator()) -> map<Key, T, Compare, Allocator>; template<class InputIterator, class Allocator> map(InputIterator, InputIterator, Allocator) -> map<iter-key-type<InputIterator>, iter-mapped-type<InputIterator>, less<iter-key-type<InputIterator>>, Allocator>; template<ranges::input_range R, class Allocator> map(from_range_t, R&&, Allocator) -> map<range-key-type<R>, range-mapped-type<R>, less<range-key-type<R>>, Allocator>; template<class Key, class T, class Allocator> map(initializer_list<pair<Key, T>>, Allocator) -> map<Key, T, less<Key>, Allocator>; }