C++ Map Library - key_comp() Function

---

---

Description

The C++ function std::map::key_comp() returns a function object that compares the keys, which is a copy of this container's constructor argument comp.

Declaration

Following is the declaration for std::map::key_comp() function form std::map header.

C++98

key_compare key_comp() const;

Parameters

None

Return value

Returns a key comparison function object.

Exceptions

This member function doesn't throw exception.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::map::key_comp() function.

#include <iostream>
#include <map>

using namespace std;

int main(void) {
   /* Initializer_list constructor */
   map<char, int> m = {
            {'a', 1},
            {'b', 2},
            {'c', 3},
            {'d', 4},
            {'e', 5},
            };

   auto comp = m.key_comp();
   char last = m.rbegin()->first;
   auto it = m.begin();

   cout << "Map contains following elements" << endl;

   do
      cout << it->first << " = " << it->second << endl;
   while (comp((*it++).first, last));

   return 0;
}

Let us compile and run the above program, this will produce the following result −

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