
Category: containers  Component type: type 
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.
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; }
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 
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. 
[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.
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