C++ Map Library - count() Function

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Description

The C++ function std::map::count() returns number of mapped values associated with key k.

As this container does not allow duplicates value is alway either 0 or 1.

Declaration

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

C++98

size_type count (const key_type& k) const;

Parameters

k − Key for search operation.

Return value

Returns 1 if container has value associated with key k otherwise 0.

Exceptions

This member function doesn't throw exception.

Time complexity

Logarithmic i.e. log(n).

Example

The following example shows the usage of std::map::count() 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},
            };

   if (m.count('a') == 1) {
      cout << "m['a'] = " << m.at('a') << endl;
   }

   if (m.count('z') == 0) {
      cout << "Value not present for key m['z']" << endl;
   }

   return 0;
}

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

m['a'] = 1
Value not present for key m['z']