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# Standard library header <map>

From cppreference.com
< cpp‎ | header

This header is part of the containers library.

### Classes
map | collection of key-value pairs, sorted by keys, keys are unique (class template) [edit]
multimap | collection of key-value pairs, sorted by keys (class template) [edit]
### Functions
operator==operator!=operator<operator<=operator>operator>= | lexicographically compares the values in the map (function template) [edit]
std::swap(std::map) | specializes the std::swap algorithm (function template) [edit]
operator==operator!=operator<operator<=operator>operator>= | lexicographically compares the values in the multimap (function template) [edit]
std::swap(std::multimap) | specializes the std::swap algorithm (function template) [edit]

### [edit] Synopsis

    #include <initializer_list>

    namespace std {
        template <class Key, class T, class Compare = less<Key>,
                  class Allocator = allocator<pair<const Key, T> > >
            class map;

        template <class Key, class T, class Compare, class Allocator>
            bool operator==(const map<Key,T,Compare,Allocator>& x,
                            const map<Key,T,Compare,Allocator>& y);
        template <class Key, class T, class Compare, class Allocator>
            bool operator< (const map<Key,T,Compare,Allocator>& x,
                            const map<Key,T,Compare,Allocator>& y);
        template <class Key, class T, class Compare, class Allocator>
            bool operator!=(const map<Key,T,Compare,Allocator>& x,
                            const map<Key,T,Compare,Allocator>& y);
        template <class Key, class T, class Compare, class Allocator>
            bool operator> (const map<Key,T,Compare,Allocator>& x,
                            const map<Key,T,Compare,Allocator>& y);
        template <class Key, class T, class Compare, class Allocator>
            bool operator>=(const map<Key,T,Compare,Allocator>& x,
                            const map<Key,T,Compare,Allocator>& y);
        template <class Key, class T, class Compare, class Allocator>
            bool operator<=(const map<Key,T,Compare,Allocator>& x,
                            const map<Key,T,Compare,Allocator>& y);

        template <class Key, class T, class Compare, class Allocator>
            void swap(map<Key,T,Compare,Allocator>& x,
                      map<Key,T,Compare,Allocator>& y);

        template <class Key, class T, class Compare = less<Key>,
                  class Allocator = allocator<pair<const Key, T> > >
            class multimap;

        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);

        template <class Key, class T, class Compare, class Allocator>
            void swap(multimap<Key,T,Compare,Allocator>& x,
                      multimap<Key,T,Compare,Allocator>& y);
    }

#### [edit] Class std::map

    template <class Key, class T, class Compare = less<Key>,
              class Allocator = allocator<pair<const Key, T> > >
    class map {
    public:
        // types:
        typedef Key                                                 key_type;
        typedef T                                                   mapped_type;
        typedef pair<const Key, T>                                  value_type;
        typedef Compare                                             key_compare;
        typedef Allocator                                           allocator_type;
        typedef value_type&                                         reference;
        typedef const value_type&                                   const_reference;
        typedef /*implementation-defined*/                          iterator;
        typedef /*implementation-defined*/                          const_iterator;
        typedef /*implementation-defined*/                          size_type;
        typedef /*implementation-defined*/                          difference_type;
        typedef typename allocator_traits<Allocator>::pointer       pointer;
        typedef typename allocator_traits<Allocator>::const_pointer const_pointer;
        typedef std::reverse_iterator<iterator>                     reverse_iterator;
        typedef std::reverse_iterator<const_iterator>               const_reverse_iterator;

        class value_compare {
            friend class map;
        protected:
            Compare comp;
            value_compare(Compare c) : comp(c) {}
        public:
            typedef bool        result_type;
            typedef value_type  first_argument_type;
            typedef value_type  second_argument_type;
            bool operator()(const value_type& x, const value_type& y) const {
                return comp(x.first, y.first);
            }
        };

        explicit map(const Compare& comp = Compare(),
                     const Allocator& = Allocator());
        template <class InputIterator>
            map(InputIterator first, InputIterator last,
                const Compare& comp = Compare(), const Allocator& = Allocator());
        map(const map<Key,T,Compare,Allocator>& x);
        map(map<Key,T,Compare,Allocator>&& x);
        explicit map(const Allocator&);
        map(const map&, const Allocator&);
        map(map&&, const Allocator&);
        map(initializer_list<value_type>,
            const Compare& = Compare(),
            const Allocator& = Allocator());

        ~map();

        map<Key,T,Compare,Allocator>&
            operator=(const map<Key,T,Compare,Allocator>& x);
        map<Key,T,Compare,Allocator>&
            operator=(map<Key,T,Compare,Allocator>&& x);
        map& 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() noexcept;
        const_iterator          cend() 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;

        // element access:
        T& operator[](const key_type& x);
        T& operator[](key_type&& x);
        T&       at(const key_type& x);
        const T& at(const key_type& x) const;

        // 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& x);
        template <class P> pair<iterator, bool> insert(P&& x);
            iterator insert(const_iterator position, const value_type& x);
        template <class P>
            iterator insert(const_iterator position, P&&);
        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& x);
        iterator erase(const_iterator first, const_iterator last);
        void swap(map<Key,T,Compare,Allocator>&);
        void clear() noexcept;

        // 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;
        size_type       count(const key_type& x) const;

        iterator        lower_bound(const key_type& x);
        const_iterator  lower_bound(const key_type& x) const;
        iterator        upper_bound(const key_type& x);
        const_iterator  upper_bound(const key_type& x) const;

        pair<iterator,iterator>
            equal_range(const key_type& x);
        pair<const_iterator,const_iterator>
            equal_range(const key_type& x) const;
    };

#### [edit] Class std::multimap

    template <class Key, class T, class Compare = less<Key>,
              class Allocator = allocator<pair<const Key, T> > >
    class multimap {
    public:
        // types:
        typedef Key                                                 key_type;
        typedef T                                                   mapped_type;
        typedef pair<const Key, T>                                  value_type;
        typedef Compare                                             key_compare;
        typedef Allocator                                           allocator_type;
        typedef value_type&                                         reference;
        typedef const value_type&                                   const_reference;
        typedef /*implementation-defined*/                          iterator;
        typedef /*implementation-defined*/                          const_iterator;
        typedef /*implementation-defined*/                          size_type;
        typedef /*implementation-defined*/                          difference_type;
        typedef typename allocator_traits<Allocator>::pointer       pointer;
        typedef typename allocator_traits<Allocator>::const_pointer const_pointer;
        typedef std::reverse_iterator<iterator>                     reverse_iterator;
        typedef std::reverse_iterator<const_iterator>               const_reverse_iterator;

        class value_compare {
            friend class multimap;
        protected:
            Compare comp;
            value_compare(Compare c) : comp(c) {}
        public:
            typedef bool        result_type;
            typedef value_type  first_argument_type;
            typedef value_type  second_argument_type;
            bool operator()(const value_type& x, const value_type& y) const {
                return comp(x.first, y.first);
            }
        };

        explicit multimap(const Compare& comp = Compare(),
                     const Allocator& = Allocator());
        template <class InputIterator>
            multimap(InputIterator first, InputIterator last,
                const Compare& comp = Compare(), const Allocator& = Allocator());
        multimap(const multimap<Key,T,Compare,Allocator>& x);
        multimap(multimap<Key,T,Compare,Allocator>&& 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());

        ~multimap();

        multimap<Key,T,Compare,Allocator>&
            operator=(const multimap<Key,T,Compare,Allocator>& x);
        multimap<Key,T,Compare,Allocator>&
            operator=(multimap<Key,T,Compare,Allocator>&& x);
        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() noexcept;
        const_iterator          cend() 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;

        // 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& x);
        template <class P> pair<iterator, bool> insert(P&& x);
            iterator insert(const_iterator position, const value_type& x);
        template <class P>
            iterator insert(const_iterator position, P&&);
        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& x);
        iterator erase(const_iterator first, const_iterator last);
        void swap(multimap<Key,T,Compare,Allocator>&);
        void clear() noexcept;

        // observers:
        key_compare   key_comp() const;
        value_compare value_comp() const;

        //multimap operations:
        iterator        find(const key_type& x);
        const_iterator  find(const key_type& x) const;
        size_type       count(const key_type& x) const;

        iterator        lower_bound(const key_type& x);
        const_iterator  lower_bound(const key_type& x) const;
        iterator        upper_bound(const key_type& x);
        const_iterator  upper_bound(const key_type& x) const;

        pair<iterator,iterator>
            equal_range(const key_type& x);
        pair<const_iterator,const_iterator>
            equal_range(const key_type& x) const;
    };

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