multimap::equal_range
Finds the range of elements where the key of the element matches a specified value.
pair <const_iterator, const_iterator> equal_range (
const Key& _Key
) const;
pair <iterator, iterator> equal_range (
const Key& _Key
);
Parameters
- _Key
The argument key to be compared with the sort key of an element from the multimap being searched.
Return Value
A pair of iterators such that the first is the lower_bound of the key and the second is the upper_bound of the key.
To access the first iterator of a pair pr returned by the member function, use pr.first and to dereference the lower bound iterator, use *(pr.first). To access the second iterator of a pair pr returned by the member function, use pr.second and to dereference the upper bound iterator, use *(pr.second).
Example
// multimap_equal_range.cpp
// compile with: /EHsc
#include <map>
#include <iostream>
int main( )
{
using namespace std;
typedef multimap <int, int, less<int> > IntMMap;
IntMMap m1;
multimap <int, int> :: const_iterator m1_RcIter;
typedef pair <int, int> Int_Pair;
m1.insert ( Int_Pair ( 1, 10 ) );
m1.insert ( Int_Pair ( 2, 20 ) );
m1.insert ( Int_Pair ( 3, 30 ) );
pair <IntMMap::const_iterator, IntMMap::const_iterator> p1, p2;
p1 = m1.equal_range( 2 );
cout << "The lower bound of the element with "
<< "a key of 2 in the multimap m1 is: "
<< p1.first -> second << "." << endl;
cout << "The upper bound of the element with "
<< "a key of 2 in the multimap m1 is: "
<< p1.second -> second << "." << endl;
// Compare the upper_bound called directly
m1_RcIter = m1.upper_bound( 2 );
cout << "A direct call of upper_bound( 2 ) gives "
<< m1_RcIter -> second << "," << endl
<< " matching the 2nd element of the pair"
<< " returned by equal_range( 2 )." << endl;
p2 = m1.equal_range( 4 );
// If no match is found for the key,
// both elements of the pair return end( )
if ( ( p2.first == m1.end( ) ) && ( p2.second == m1.end( ) ) )
cout << "The multimap m1 doesn't have an element "
<< "with a key less than 4." << endl;
else
cout << "The element of multimap m1 with a key >= 40 is: "
<< p1.first -> first << "." << endl;
}
The lower bound of the element with a key of 2 in the multimap m1 is: 20. The upper bound of the element with a key of 2 in the multimap m1 is: 30. A direct call of upper_bound( 2 ) gives 30, matching the 2nd element of the pair returned by equal_range( 2 ). The multimap m1 doesn't have an element with a key less than 4.
Requirements
Header: <map>
Namespace: std