multimap::value_comp Function in C++ STL

In this article we will be discussing the working, syntax and examples of multimap::value_comp() function in C++ STL.

What is Multimap in C++ STL?

Multimaps are the associative containers, which are similar to map containers. It also facilitates to store the elements formed by a combination of key-value and mapped value in a specific order. In a multimap container there can be multiple elements associated with the same key. The data is internally always sorted with the help of its associated keys.

What is multimap::value_comp()?

multimap::value_comp() is an inbuilt function in C++ STL which is declared in <map> header file. value_comp() returns a copy of the comparison object, which is used by the multimap container for the comparisons. By default, this object is less than the operator’s object, which works similarly to a less-than operator.

It is a type of function pointer or a function object which do the comparison of the two values of the same type in a particular multimap and returns true if the first element is smaller than the second element in the container, else it returns false.

Syntax

multi_name.value_comp();

Parameter

This function accepts no parameter.

Return value

This function returns a comparison object of the associated multimap container.

Input

multimap<char, int> newmap;
newmap(make_pair(‘a’, 1));
newmap(make_pair(‘b’, 2));
newmap(make_pair(‘c’, 3));
multimap<int>::value_compare cmp = myset.value_comp();

Output

1
2
3

Example

 Live Demo

#include <iostream>
#include <map>
using namespace std;
int main(){
   multimap<int, char> mul;
   //inserting elements at given key
   mul.insert(make_pair(0, 'A'));
   mul.insert(make_pair(1, 'B'));
   mul.insert(make_pair(2, 'C'));
   mul.insert(make_pair(3, 'D'));
   pair<int, char> temp = *mul.rbegin();
   multimap<int, char>::iterator it = mul.begin();
   cout<<"Elements at given key is : "<<'\n';
   do {
      cout << (*it).first << " = " << (*it).second << '\n';
   }
   while (mul.value_comp()(*it++, temp));
      return 0;
}

Output

If we run the above code it will generate the following output −

Elements at given key is :
0 = A
1 = B
2 = C
3 = D