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multiset<Key, Compare, Alloc>


Category: containers	Component type: type

Description

Multiset is a Sorted Associative Container that stores objects of type Key. Multiset is a Simple Associative Container, meaning that its value type, as well as its key type, is Key. It is also a Multiple Associative Container, meaning that two or more elements may be identical.

Set and multiset are particularly well suited to the set algorithms includes, set_union, set_intersection, set_difference, and set_symmetric_difference. The reason for this is twofold. First, the set algorithms require their arguments to be sorted ranges, and, since set and multiset are Sorted Associative Containers, their elements are always sorted in ascending order. Second, the output range of these algorithms is always sorted, and inserting a sorted range into a set or multiset is a fast operation: the Unique Sorted Associative Container and Multiple Sorted Associative Container requirements guarantee that inserting a range takes only linear time if the range is already sorted.

Multiset has the important property that inserting a new element into a multiset does not invalidate iterators that point to existing elements. Erasing an element from a multiset also does not invalidate any iterators, except, of course, for iterators that actually point to the element that is being erased.

Example

int main()
{
  const int N = 10;
  int a[N] = {4, 1, 1, 1, 1, 1, 0, 5, 1, 0};
  int b[N] = {4, 4, 2, 4, 2, 4, 0, 1, 5, 5};

  multiset<int> A(a, a + N);
  multiset<int> B(b, b + N);
  multiset<int> C;

  cout << "Set A: ";
  copy(A.begin(), A.end(), ostream_iterator<int>(cout, " "));
  cout << endl;
  cout << "Set B: ";
  copy(B.begin(), B.end(), ostream_iterator<int>(cout, " "));   
  cout << endl;

  cout << "Union: ";
  set_union(A.begin(), A.end(), B.begin(), B.end(),
            ostream_iterator<int>(cout, " "));
  cout << endl;

  cout << "Intersection: ";
  set_intersection(A.begin(), A.end(), B.begin(), B.end(),
                   ostream_iterator<int>(cout, " "));
  cout << endl;  

  set_difference(A.begin(), A.end(), B.begin(), B.end(),
                 inserter(C, C.begin()));
  cout << "Set C (difference of A and B): ";
  copy(C.begin(), C.end(), ostream_iterator<int>(cout, " "));
  cout << endl;
}

Definition

Defined in the standard header set, and in the nonstandard backward-compatibility header multiset.h.

Template parameters

Parameter	Description	Default
`Key`	The set's key type and value type. This is also defined as `multiset::key_type` and `multiset::value_type`
`Compare`	The key comparison function, a Strict Weak Ordering whose argument type is `key_type`; it returns `true` if its first argument is less than its second argument, and `false` otherwise. This is also defined as `multiset::key_compare` and `multiset::value_compare`.	`less<Key>`
`Alloc`	The `multiset`'s allocator, used for all internal memory management.	`alloc`

Model of

Multiple Sorted Associative Container, Simple Associative Container

Type requirements

Key is Assignable.
Compare is a Strict Weak Ordering whose argument type is Key.
Alloc is an Allocator.

Public base classes

None.

Members

Member	Where defined	Description
`value_type`	Container	The type of object, `T`, stored in the multiset.
`key_type`	Associative Container	The key type associated with `value_type`.
`key_compare`	Sorted Associative Container	Function object that compares two keys for ordering.
`value_compare`	Sorted Associative Container	Function object that compares two values for ordering.
`pointer`	Container	Pointer to `T`.
`reference`	Container	Reference to `T`
`const_reference`	Container	Const reference to `T`
`size_type`	Container	An unsigned integral type.
`difference_type`	Container	A signed integral type.
`iterator`	Container	Iterator used to iterate through a `multiset`.
`const_iterator`	Container	Const iterator used to iterate through a `multiset`. (`Iterator` and `const_iterator` are the same type.)
`reverse_iterator`	Reversible Container	Iterator used to iterate backwards through a `multiset`.
`const_reverse_iterator`	Reversible Container	Const iterator used to iterate backwards through a `multiset`. (`Reverse_iterator` and `const_reverse_iterator` are the same type.)
`iterator begin() const`	Container	Returns an `iterator` pointing to the beginning of the `multiset`.
`iterator end() const`	Container	Returns an `iterator` pointing to the end of the `multiset`.
`reverse_iterator rbegin() const`	Reversible Container	Returns a `reverse_iterator` pointing to the beginning of the reversed multiset.
`reverse_iterator rend() const`	Reversible Container	Returns a `reverse_iterator` pointing to the end of the reversed multiset.
`size_type size() const`	Container	Returns the size of the `multiset`.
`size_type max_size() const`	Container	Returns the largest possible size of the `multiset`.
`bool empty() const`	Container	`true` if the `multiset`'s size is `0`.
`key_compare key_comp() const`	Sorted Associative Container	Returns the `key_compare` object used by the `multiset`.
`value_compare value_comp() const`	Sorted Associative Container	Returns the `value_compare` object used by the `multiset`.
`multiset()`	Container	Creates an empty `multiset`.
`multiset(const key_compare& comp)`	Sorted Associative Container	Creates an empty `multiset`, using `comp` as the `key_compare` object.
template <class InputIterator> multiset(InputIterator f, InputIterator l) [1]	Multiple Sorted Associative Container	Creates a multiset with a copy of a range.
template <class InputIterator> multiset(InputIterator f, InputIterator l, const key_compare& comp) [1]	Multiple Sorted Associative Container	Creates a multiset with a copy of a range, using `comp` as the `key_compare` object.
`multiset(const multiset&)`	Container	The copy constructor.
`multiset& operator=(const multiset&)`	Container	The assignment operator
`void swap(multiset&)`	Container	Swaps the contents of two multisets.
`iterator insert(const value_type& x)`	Multiple Associative Container	Inserts `x` into the `multiset`.
iterator insert(iterator pos, const value_type& x)	Multiple Sorted Associative Container	Inserts `x` into the `multiset`, using `pos` as a hint to where it will be inserted.
template <class InputIterator> void insert(InputIterator, InputIterator) [1]	Multiple Sorted Associative Container	Inserts a range into the `multiset`.
`void erase(iterator pos)`	Associative Container	Erases the element pointed to by `pos`.
`size_type erase(const key_type& k)`	Associative Container	Erases the element whose key is `k`.
`void erase(iterator first, iterator last)`	Associative Container	Erases all elements in a range.
`void clear()`	Associative Container	Erases all of the elements.
`iterator find(const key_type& k) const`	Associative Container	Finds an element whose key is `k`.
`size_type count(const key_type& k) const`	Associative Container	Counts the number of elements whose key is `k`.
`iterator lower_bound(const key_type& k) const`	Sorted Associative Container	Finds the first element whose key is not less than `k`.
`iterator upper_bound(const key_type& k) const`	Sorted Associative Container	Finds the first element whose key greater than `k`.
pair<iterator, iterator> equal_range(const key_type& k) const	Sorted Associative Container	Finds a range containing all elements whose key is `k`.
bool operator==(const multiset&, const multiset&)	Forward Container	Tests two multisets for equality. This is a global function, not a member function.
bool operator<(const multiset&, const multiset&)	Forward Container	Lexicographical comparison. This is a global function, not a member function.

New members

All of multiset's members are defined in the Multiple Sorted Associative Container and Simple Associative Container requirements. Multiset does not introduce any new members.

Notes

[1] This member function relies on member template functions, which at present (early 1998) are not supported by all compilers. If your compiler supports member templates, you can call this function with any type of input iterator. If your compiler does not yet support member templates, though, then the arguments must either be of type const value_type* or of type multiset::const_iterator.