map count() Function in C++ STL

The std::map::count() in C++ is a built-in function that is used to count the occurrence of the given key in the map container. It is the member function of the std::map container.

In this article, we will learn how to use std::map::count() in C++.

Syntax

mp.count(key)

Parameters

• key: The value whose occurrence is to be searched.

Return Value

• Returns 1, if the key is present in the map container, as the key is always unique in the map.
• Returns 0, if the key is not present in the map.

Example of map::count()

Count of 1: 1
Count of 9: 0

Time Complexity: O(log n), where n is the number of key in the map container.
Auxiliary Space: O(1)

Why map::count() exists?

std::map() container does not store the duplicate values, so why map::count() is needed as we can already check the existence of an element in a map using std::find() or map::find() functions.

Other containers such as multimap may contain more than one copy of the key. So the reason is that the containers in C++ STL are required to implement the count() function is to help in generic programming.