public member function
<set>

std::set::count

size_type count (const value_type& val) const;
Count elements with a specific value
Searches the container for elements equivalent to val and returns the number of matches.

Because all elements in a set container are unique, the function can only return 1 (if the element is found) or zero (otherwise).

Two elements of a set are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the elements are passed as arguments).

Parameters

val
Value to search for.
Member type value_type is the type of the elements in the container, defined in set as an alias of its first template parameter (T).

Return value

1 if the container contains an element equivalent to val, or zero otherwise.

Member type size_type is an unsigned integral type.

Example

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// set::count
#include <iostream>
#include <set>

int main ()
{
  std::set<int> myset;

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

  for (int i=0; i<10; ++i)
  {
    std::cout << i;
    if (myset.count(i)!=0)
      std::cout << " is an element of myset.\n";
    else
      std::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

Logarithmic in size.

Iterator validity

No changes.

Data races

The container is accessed.
Concurrently accessing the elements of a set is safe.

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the container.

See also

set::find
Get iterator to element (public member function )
set::size
Return container size (public member function )
set::equal_range
Get range of equal elements (public member function )

C++