multiset

Container Class

• Summary
• Data Type and Member Function Indexes
• Synopsis
• Description
• Interface
• Constructors
• Destructors
• Assignment Operators
• Allocators
• Iterators
• Member Functions
• Non-member Operators
• Specialized Algorithms
• Example
• Warnings
• See Also

An associative container that allows fast access to stored key values. Storage of duplicate keys is allowed. A multiset supports bidirectional iterators.

Member Functions
begin() clear() count() empty() end() equal_range()	erase() find() get_allocator() insert() key_comp() lower_bound()	max_size() operator!=() operator>() operator>=() operator<() operator<=()	operator=() operator==() rbegin() rend() size() swap() upper_bound() value_comp()

#include <set>
template <class Key, class Compare = less<Key>,
          class Allocator = allocator<Key> > 
class multiset;

multiset <Key, Compare, Allocator> allows fast access to stored key values. The default operation for key comparison is the < operator. Insertion of duplicate keys is allowed with a multiset.

multiset uses bidirectional iterators that point to a stored key.

Any type used for the template parameter Key must include the following (where T is the type, t is a value of T and u is a const value of T):

The type used for the Compare template parameter must satisfy the requirements for binary functions.

template <class Key, class Compare = less<Key>, 
          class Allocator = allocator<Key> >
 class multiset {

public:

// typedefs

   typedef Key key_type;
   typedef Key value_type;
   typedef Compare key_compare;
   typedef Compare value_compare;
   typedef Allocator allocator_type;


   typedef typename
           Allocator::reference        reference;
   typedef typename
           Allocator::const_reference  const_reference;


   class iterator;
   class const_iterator;


   typedef typename
           Allocator::size_type        size_type;
   typedef typename
           Allocator::difference_type  difference_type;


   typedef typename std::reverse_iterator<iterator>
                         reverse_iterator;
   typedef typename std::reverse_iterator<const_iterator>
                         const_reverse_iterator;

// Construct/Copy/Destroy

   explicit multiset (const Compare& = Compare(),
                      const Allocator& = Allocator());
   template <class InputIterator>
    multiset (InputIterator, InputIterator,
              const Compare& = Compare(),
              const Allocator& = Allocator());
   multiset (const multiset<Key, Compare, Allocator>&);
   ~multiset ();
   multiset<Key, Compare, Allocator>& 
            operator= (const multiset<Key, 
                       Compare, Allocator>&);

// Iterators

   iterator begin ();
   const_iterator begin () const;
   iterator end ();
   const_iterator end () const;
   reverse_iterator rbegin ();
   const_reverse_iterator rbegin () const;
   reverse_iterator rend ();
   const_reverse_iterator rend () const;

// Capacity

   bool empty () const;
   size_type size () const;
   size_type max_size () const;

// Modifiers

   iterator insert (const value_type&);
   iterator insert (iterator, const value_type&);
   template <class InputIterator>
    void insert (InputIterator, InputIterator);

   void erase (iterator);
   size_type erase (const key_type&);
   void erase (iterator, iterator);
   void swap (multiset<Key, Compare, Allocator>&);
   void clear ();

// Observers

   key_compare key_comp () const;
   value_compare value_comp () const;

// Multiset operations

   iterator find (const key_type&) const;
   size_type count (const key_type&) const;
   iterator lower_bound (const key_type&) const;
   iterator upper_bound (const key_type&) const;
   pair<iterator, iterator> equal_range 
       (const key_type&) const;
   };

// Non-member Operators

template <class Key, class Compare, class Allocator>
 bool operator==
    (const multiset<Key, Compare, Allocator>&,
     const multiset<Key, Compare, Allocator>&);

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

template <class Key, class Compare, class Allocator>
 bool operator<
    (const multiset<Key, Compare, Allocator>&,
     const multiset<Key, Compare, Allocator>&);

template <class Key, class Compare, class Allocator>
 bool operator>
    (const multiset<Key, Compare, Allocator>&,
     const multiset<Key, Compare, Allocator>&);

template <class Key, class Compare, class Allocator>
 bool operator<=
    (const multiset<Key, Compare, Allocator>&,
     const multiset<Key, Compare, Allocator>&);

template <class Key, class Compare, class Allocator>
 bool operator>=
    (const multiset<Key, Compare, Allocator>&,
     const multiset<Key, Compare, Allocator>&);

// Specialized Algorithms

template <class Key, class Compare, class Allocator>
 void swap ( multiset<Key, Compare, Allocator>&,
             multiset<Key, Compare, Allocator>&);

explicit multiset(const Compare& comp = Compare(),
                   const Allocator& alloc = Allocator());

Constructs an empty multiset that uses the optional relation comp to order keys, if it is supplied, and the allocator alloc for all storage management.

template <class InputIterator>
multiset(InputIterator first, InputIterator last,
          const Compare& = Compare(),
          const Allocator& = Allocator());

Constructs a multiset containing values in the range [first, last).

multiset(const multiset<Key, Compare, Allocator>& x);

Creates a new multiset by copying all key values from x.

~multiset();

Releases any allocated memory for this multiset.

multiset<Key, Compare, Allocator>& 
operator=(const multiset<Key, Compare, Allocator>& x);

Replaces the contents of *this with a copy of the contents of x.

allocator_type 
get_allocator() const;

Returns a copy of the allocator used by self for storage management.

iterator 
begin();

Returns an iterator pointing to the first element stored in the multiset. "First" is defined by the multiset's comparison operator, Compare.

const_iterator 
begin();

Returns a const_iterator pointing to the first element stored in the multiset.

iterator 
end();

Returns an iterator pointing to the last element stored in the multiset (in other words, the off-the-end value).

const_iterator 
end();

Returns a const_iterator pointing to the last element stored in the multiset (in other words, the off-the-end value).

reverse_iterator 
rbegin();

Returns a reverse_iterator pointing to the first element stored in the multiset. "First" is defined by the multiset's comparison operator, Compare.

const_reverse_iterator 
rbegin();

Returns a const_reverse_iterator pointing to the first element stored in the multiset.

reverse_iterator 
rend();

Returns a reverse_iterator pointing to the last element stored in the multiset (in other words, the off-the-end value).

const_reverse_iterator 
rend();

Returns a const_reverse_iterator pointing to the last element stored in the multiset (in other words, the off-the-end value).

void
clear();

Erases all elements from the self.

size_type 
count(const key_type& x) const;

Returns the number of elements in the multiset with the key value x.

bool 
empty() const;

Returns true if the multiset is empty, false otherwise.

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

Returns the pair (lower_bound(x), upper_bound(x)).

size_type 
erase(const key_type& x);

Deletes all elements with the key value x from the multiset, if any exist. Returns the number of deleted elements.

void
erase(iterator position);

Deletes the multiset element pointed to by the iterator position. Returns an iterator pointing to the element following the deleted element, or end(), if the deleted item was the last one in this list.

void
erase(iterator first, iterator last);

If the iterators first and last point to the same multiset and last is reachable from first, all elements in the range (first, last) are deleted from the multiset. Returns an iterator pointing to the element following the last deleted element or end(), if there were no elements after the deleted range.

iterator 
find(const key_type& x) const;

Searches the multiset for a key value x and returns an iterator to that key if it is found. If such a value is not found, the iterator end() is returned.

iterator 
insert(const value_type& x);
iterator 
insert(iterator position, const value_type& x);

x is inserted into the multiset. A position may be supplied as a hint regarding where to do the insertion. If the insertion is done right after position, then it takes amortized constant time. Otherwise, it takes O(log N) time.

template <class InputIterator>
void 
insert(InputIterator first, InputIterator last);

Copies of each element in the range [first, last) are inserted into the multiset. This insert takes approximately O(N*log(size()+N)) time.

key_compare 
key_comp() const;

Returns a function object capable of comparing key values using the comparison operation, Compare, of the current multiset.

iterator 
lower_bound(const key_type& x) const;

Returns an iterator to the first element whose key is greater than or equal to x. If no such element exists, end() is returned.

size_type 
max_size() const;

Returns the maximum possible size of the multiset size_type.

size_type
size() const;

Returns the number of elements in the multiset.

void 
swap(multiset<Key, Compare, Allocator>& x);

Swaps the contents of the multiset x with the current multiset, *this.

iterator 
upper_bound(const key_type& x) const;

Returns an iterator to the first element whose key is smaller than or equal to x. If no such element exists, then end() is returned.

value_compare 
value_comp() const;

Returns a function object capable of comparing key values using the comparison operation, Compare, of the current multiset.

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

Returns true if all elements in x are element-wise equal to all elements in y, using (T::operator==). Otherwise it returns false.

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

Returns !(x==y).

template <class Key, class Compare, class Allocator>
operator<(const multiset<Key, Compare, Allocator>& x,
           const multiset<Key, Compare, Allocator>& y);

Returns true if x is lexicographically less than y. Otherwise, it returns false.

template <class Key, class Compare, class Allocator>
operator>(const multiset<Key, Compare, Allocator>& x,
           const multiset<Key, Compare, Allocator>& y);

Returns y < x.

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

Returns !(y < x).

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

Returns !(x < y).

template <class Key, class Compare, class Allocator>
void swap(multiset<Key,Compare,Allocator>& a,
           multiset<Key,Compare,Allocator>&b);

Swaps the contents of a and b.

//
// multiset.cpp
//
#include <set>
#include <iostream>
using namespace std;

 typedef multiset<int, less<int>, allocator> set_type;

 ostream& operator<<(ostream& out, const set_type& s)
 {
   copy(s.begin(),s.end(),
     ostream_iterator<set_type::value_type,char>(cout," "));
   return out;
 }


 int main(void)
 {
   // create a multiset of ints
   set_type  si;
   int  i;

   for (int j = 0; j < 2; j++)
   {
     for(i = 0; i < 10; ++i) {
       // insert values with a hint
       si.insert(si.begin(), i);
     }
   }

   // print out the multiset
   cout << si << endl;

   // Make another int multiset and an empty multiset
   set_type si2, siResult;
   for (i = 0; i < 10; i++)
      si2.insert(i+5);
   cout << si2 << endl;

   // Try a couple of set algorithms
   set_union(si.begin(),si.end(),si2.begin(),si2.end(),
          inserter(siResult,siResult.begin()));
   cout << "Union:" << endl << siResult << endl;

   siResult.erase(siResult.begin(),siResult.end());
   set_intersection(si.begin(),si.end(),
          si2.begin(),si2.end(),
          inserter(siResult,siResult.begin()));
   cout << "Intersection:" << endl << siResult << endl;
  
   return 0;
 }

Program Output

0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9
5 6 7 8 9 10 11 12 13 14
Union:
0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 11 12 13 14
Intersection:
5 6 7 8 9

Member function templates are used in all containers included in the Standard Template Library. An example of this feature is the constructor for multiset<Key, Compare, Allocator>, which takes two templatized iterators:

template <class InputIterator>
multiset (InputIterator, InputIterator,
          const Compare& = Compare(),
          const Allocator& = Allocator());

multiset also has an insert function of this type. These functions, when not restricted by compiler limitations, allow you to use any type of input iterator as arguments. For compilers that do not support this feature, substitute functions allow you to use an iterator obtained from the same type of container as the one you are constructing (or calling a member function on). You can also use a pointer to the type of element you have in the container.

For example, if your compiler does not support member function templates, you can construct a multiset in the following two ways:

int intarray[10];
multiset<int> first_multiset(intarray, intarray +10);
multiset<int> second_multiset(first_multiset.begin(),
              first_multiset.end());

but not this way:

multiset<long>
 long_multiset(first_multiset.begin(),first_multiset.end());

since the long_multiset and first_multiset are not the same type.

Also, many compilers do not support default template arguments. If your compiler is one of these you always need to supply the Compare template argument and the Allocator template argument. For instance, you have to write:

multiset<int, less<int>, allocator<int> >

instead of:

multiset<int>

If your compiler does not support namespaces, then you do not need the using declaration for std.

allocator, Containers, Iterators, set