size_type count ( cont key_type& x ) const;

Count elements with a specific key

Searches the container for an element with a key of x and returns the number of times the element appears in the container. Because set containers do not allow for duplicate keys, this means that the function actually returns 1 if the element is found, and zero otherwise.

Parameters

x

Value to be searched for.
key_type is a member type defined in set containers as an alias of Key, which is the first template parameter and the type of the elements stored in the container.

Return value

Member type size_type is an unsigned integral type.

Example

// set::count
#include <iostream>
#include <set>
using namespace std;

int main ()
{
  set<int> myset;
  int i;

  // set some initial values:
  for (i=1; i<5; i++) myset.insert(i*3);    // set: 3 6 9 12

  for (i=0;i<10; i++)
  {
    cout << i;
    if (myset.count(i)>0)
      cout << " is an element of myset.\n";
    else 
      cout << " is not an element of myset.\n";
  }

  return 0;
}

Output:

0 is not an element of myset.
1 is not an element of myset.
2 is not an element of myset.
3 is an element of myset.
4 is not an element of myset.
5 is not an element of myset.
6 is an element of myset.
7 is not an element of myset.
8 is not an element of myset.
9 is an element of myset.

Complexity

See also