23 Containers library [containers]

A map is an associative container that supports unique keys (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.

A map satisfies all of the requirements of a container, of a reversible container ([container.requirements]), of an associative container ([associative.reqmts]), and of an allocator-aware container (Table [tab:containers.allocatoraware]). 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.

namespace std {
  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;       // see [container.requirements]
    typedef implementation-defined                const_iterator; // see [container.requirements]
    typedef implementation-defined                size_type;      // see [container.requirements]
    typedef implementation-defined                difference_type;// see [container.requirements]
    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);
      }
    };

    // [map.cons], construct/copy/destroy:
    map() : map(Compare()) { }
    explicit map(const Compare& comp,
                 const Allocator& = Allocator());
    template <class InputIterator>
      map(InputIterator first, InputIterator last,
          const Compare& comp = Compare(), const Allocator& = Allocator());
    map(const map& x);
    map(map&& 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());
    template <class InputIterator>
    map(InputIterator first, InputIterator last, const Allocator& a)
      : map(first, last, Compare(), a) { }
    map(initializer_list<value_type> il, const Allocator& a)
      : map(il, Compare(), a) { }
   ~map();
    map& operator=(const map& x);
    map& operator=(map&& 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() 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;

    // [map.access], 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;

    // [map.modifiers], 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&);
    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;
    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 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);

  // specialized algorithms:
  template <class Key, class T, class Compare, class Allocator>
    void swap(map<Key,T,Compare,Allocator>& x,
              map<Key,T,Compare,Allocator>& y);
}

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 ([container.requirements]), of an associative container ([associative.reqmts]), and of an allocator-aware container (Table [tab:containers.allocatoraware]). 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:
    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;       // see [container.requirements]
    typedef implementation-defined                const_iterator; // see [container.requirements]
    typedef implementation-defined                size_type;      // see [container.requirements]
    typedef implementation-defined                difference_type;// see [container.requirements]
    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);
      }
    };

    // 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);
    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;

    // 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);
    template <class P> iterator insert(P&& x);
    iterator insert(const_iterator position, const 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>);

    iterator  erase(const_iterator position);
    size_type erase(const key_type& x);
    iterator  erase(const_iterator first, const_iterator last);
    void swap(multimap&);
    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;
    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 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);

  // 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);
}

A set is an associative container that supports unique keys (contains at most one of each key value) and provides for fast retrieval of the keys themselves. The set class supports bidirectional iterators.

A set satisfies all of the requirements of a container, of a reversible container ([container.requirements]), of an associative container ([associative.reqmts]), and of an allocator-aware container (Table [tab:containers.allocatoraware]). A set also provides most operations described in ([associative.reqmts]) for unique keys. This means that a set supports the a_uniq operations in ([associative.reqmts]) but not the a_eq operations. For a set<Key> both the key_type and value_type are Key. Descriptions are provided here only for operations on set that are not described in one of these tables and for operations where there is additional semantic information.

namespace std {
  template <class Key, class Compare = less<Key>,
            class Allocator = allocator<Key> >
  class set {
  public:
    // types:
    typedef Key                                   key_type;
    typedef Key                                   value_type;
    typedef Compare                               key_compare;
    typedef Compare                               value_compare;
    typedef Allocator                             allocator_type;
    typedef value_type&                           reference;
    typedef const value_type&                     const_reference;
    typedef implementation-defined                iterator;       // See [container.requirements]
    typedef implementation-defined                const_iterator; // See [container.requirements]
    typedef implementation-defined                size_type;      // See [container.requirements]
    typedef implementation-defined                difference_type;// See [container.requirements]
    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;

    // [set.cons], construct/copy/destroy:
    set() : set(Compare()) { }
    explicit set(const Compare& comp,
                 const Allocator& = Allocator());
    template <class InputIterator>
      set(InputIterator first, InputIterator last,
          const Compare& comp = Compare(), const Allocator& = Allocator());
    set(const set& x);
    set(set&& x);
    explicit set(const Allocator&);
    set(const set&, const Allocator&);
    set(set&&, const Allocator&);
    set(initializer_list<value_type>,
      const Compare& = Compare(),
      const Allocator& = Allocator());
    template <class InputIterator>
    set(InputIterator first, InputIterator last, const Allocator& a)
      : set(first, last, Compare(), a) { }
    set(initializer_list<value_type> il, const Allocator& a)
      : set(il, Compare(), a) { }
   ~set();
    set& operator=(const set& x);
    set& operator=(set&& x);
    set& 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;

    // 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);
    pair<iterator,bool> insert(value_type&& x);
    iterator insert(const_iterator position, const value_type& x);
    iterator insert(const_iterator position, value_type&& x);
    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(set&);
    void clear() noexcept;

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

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

  // specialized algorithms:
  template <class Key, class Compare, class Allocator>
    void swap(set<Key,Compare,Allocator>& x,
              set<Key,Compare,Allocator>& y);
}

A multiset is an associative container that supports equivalent keys (possibly contains multiple copies of the same key value) and provides for fast retrieval of the keys themselves. The multiset class supports bidirectional iterators.

A multiset satisfies all of the requirements of a container, of a reversible container ([container.requirements]), of an associative container ([associative.reqmts]), and of an allocator-aware container (Table [tab:containers.allocatoraware]). multiset also provides most operations described in ([associative.reqmts]) for duplicate keys. This means that a multiset supports the a_eq operations in ([associative.reqmts]) but not the a_uniq operations. For a multiset<Key> both the key_type and value_type are Key. Descriptions are provided here only for operations on multiset that are not described in one of these tables and for operations where there is additional semantic information.

namespace std {
  template <class Key, class Compare = less<Key>,
            class Allocator = allocator<Key> >
  class multiset {
  public:
    // types:
    typedef Key                                                     key_type;
    typedef Key                                                     value_type;
    typedef Compare                                                 key_compare;
    typedef Compare                                                 value_compare;
    typedef Allocator                                               allocator_type;
    typedef value_type&                                             reference;
    typedef const value_type&                                       const_reference;
    typedef implementation-defined                iterator;       // see [container.requirements]
    typedef implementation-defined                const_iterator; // see [container.requirements]
    typedef implementation-defined                size_type;      // see [container.requirements]
    typedef implementation-defined                difference_type;// see [container.requirements]
    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;

    // construct/copy/destroy:
    multiset() : multiset(Compare()) { }
    explicit multiset(const Compare& comp,
                      const Allocator& = Allocator());
    template <class InputIterator>
      multiset(InputIterator first, InputIterator last,
               const Compare& comp = Compare(),
               const Allocator& = Allocator());
    multiset(const multiset& x);
    multiset(multiset&& x);
    explicit multiset(const Allocator&);
    multiset(const multiset&, const Allocator&);
    multiset(multiset&&, const Allocator&);
    multiset(initializer_list<value_type>,
      const Compare& = Compare(),
      const Allocator& = Allocator());
    template <class InputIterator>
    multiset(InputIterator first, InputIterator last, const Allocator& a)
      : multiset(first, last, Compare(), a) { }
    multiset(initializer_list<value_type> il, const Allocator& a)
      : multiset(il, Compare(), a) { }
   ~multiset();
    multiset& operator=(const multiset& x);
    multiset& operator=(multiset&& x);
    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;

    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;

    // 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);
    iterator insert(const_iterator position, const value_type& x);
    iterator insert(const_iterator position, value_type&& x);
    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(multiset&);
    void clear() noexcept;

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

    // set 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 Key, class Compare, class Allocator>
    bool operator==(const multiset<Key,Compare,Allocator>& x,
                    const multiset<Key,Compare,Allocator>& y);
  template <class Key, class Compare, class Allocator>
    bool operator< (const multiset<Key,Compare,Allocator>& x,
                    const multiset<Key,Compare,Allocator>& y);
  template <class Key, class Compare, class Allocator>
    bool operator!=(const multiset<Key,Compare,Allocator>& x,
                    const multiset<Key,Compare,Allocator>& y);
  template <class Key, class Compare, class Allocator>
    bool operator> (const multiset<Key,Compare,Allocator>& x,
                    const multiset<Key,Compare,Allocator>& y);
  template <class Key, class Compare, class Allocator>
    bool operator>=(const multiset<Key,Compare,Allocator>& x,
                    const multiset<Key,Compare,Allocator>& y);
  template <class Key, class Compare, class Allocator>
    bool operator<=(const multiset<Key,Compare,Allocator>& x,
                    const multiset<Key,Compare,Allocator>& y);

  // specialized algorithms:
  template <class Key, class Compare, class Allocator>
    void swap(multiset<Key,Compare,Allocator>& x,
              multiset<Key,Compare,Allocator>& y);
}