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:
explicit multiset(const Compare& comp = Compare(),
const Allocator& = Allocator());
template <class InputIterator>
multiset(InputIterator first, InputIterator last,
const Compare& comp = Compare(),
const Allocator& = Allocator());
multiset(const multiset<Key,Compare,Allocator>& x);
multiset(multiset<Key,Compare,Allocator>&& 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());
~multiset();
multiset<Key,Compare,Allocator>&
operator=(const multiset<Key,Compare,Allocator>& x);
multiset<Key,Compare,Allocator>&
operator=(multiset<Key,Compare,Allocator>&& 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<Key,Compare,Allocator>&);
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;
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;
};
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);
}