multimap key_comp in C++ STL
Last Updated :
12 Nov, 2018
This is the part of Standard Template Library(STL) of C++. To use this STL, use Namespace: std and include “map” header file in the program.
It returns the function object or comparison object or ordering delegate that compares the keys, which is a copy of this container’s constructor argument.
It is a function pointer or an object that takes two arguments of the same type as the element keys and determines the order of the elements in the container.
Syntax:
key_compare key_comp();
Here key_compare is the type of the comparison object, which is associated to the container.
Parameters:
It does not accept any parameter.
Returns:
It returns the key comparison function object or ordering delegate, which is defined in multimap as an alias of its third template parameter.
Below is an example of multimap::key_comp:
#include <iostream>
#include <map>
using namespace std;
int main()
{
multimap< char , int > m1;
multimap< char , int >::key_compare comp = m1.key_comp();
m1.insert(make_pair( 'a' , 10));
m1.insert(make_pair( 'b' , 20));
m1.insert(make_pair( 'b' , 30));
m1.insert(make_pair( 'c' , 40));
char h = m1.rbegin()->first;
multimap< char , int >::iterator i = m1.begin();
do {
cout << (*i).first << " = " << (*i).second << '\n' ;
} while (comp((*i++).first, h));
return 0;
}
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Output:
a = 10
b = 20
b = 30
c = 40
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