map value_comp() in C++ STL

The std::map::value_comp() is a function in C++ STL. It returns a function object that compares objects of type std::map::value.

Syntax:

value_compare value_comp() const

Parameters: It does not accept any parameters.

Returns: This method returns a function object that compares objects of type std::map::value.

Time Complexity: O(1)

Below examples illustrate the map::value_comp() method:

Example 1:

// C++ program to illustrate 
// map::value_comp() method 
  
#include <iostream> 
#include <map> 
using namespace std; 
  
int main() 
{ 
    map<char, int> m = { 
        { 'a', 1 }, 
        { 'b', 2 }, 
        { 'c', 3 }, 
        { 'd', 4 }, 
        { 'e', 5 }, 
    }; 
  
    auto last = *m.rbegin(); 
    auto i = m.begin(); 
  
    cout << "Map contains "
         << "following elements"
         << endl; 
  
    do { 
  
        cout << i->first 
             << " = "
             << i->second 
             << endl; 
    } while (m.value_comp()(*i++, last)); 
  
    return 0; 
} 

Output:

Map contains following elements
a = 1
b = 2
c = 3
d = 4
e = 5

Example 2:

// C++ Program to illustrate 
// map::rbegin() method 
  
#include <iostream> 
#include <map> 
using namespace std; 
  
int main() 
{ 
  
    map<char, char> m = { 
        { 'a', 'A' }, 
        { 'b', 'B' }, 
        { 'c', 'C' }, 
        { 'd', 'D' }, 
        { 'e', 'E' }, 
    }; 
  
    auto last = *m.rbegin(); 
    auto i = m.begin(); 
  
    cout << "Map contains "
         << "following elements"
         << endl; 
  
    do { 
  
        cout << i->first 
             << " = "
             << i->second 
             << endl; 
    } while (m.value_comp()(*i++, last)); 
  
    return 0; 
} 

Output:

Map contains following elements
a = A
b = B
c = C
d = D
e = E

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