C++ Unordered_set Library - count

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Description

It is used to search for the container of elements with a value of k and returns the number of elements found

Declaration

Following is the declaration for std::unordered_set::count.

C++11

size_type count ( const key_type& k ) const;

Parameters

k − K is the search element.

Return value

It returns if an element with a value equivalent to k is found, or zero otherwise.

Exceptions

Exception is thrown if any element comparison object throws exception.

Please note that invalid arguments cause undefined behavior.

Time complexity

constant time.

Example

The following example shows the usage of std::unordered_set::count.

#include <iostream>
#include <string>
#include <unordered_set>

int main () {
   std::unordered_set<std::string> myset = { "sairam", "krishna", "prasad" };

   for (auto& x: {"tutorialspoint","sairam","krishna","t-shirt"}) {
      if (myset.count(x)>0)
         std::cout << "myset has " << x << std::endl;
      else
         std::cout << "myset has no " << x << std::endl;
   }

   return 0;
}

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

myset has no tutorialspoint
myset has sairam
myset has krishna
myset has no t-shirt