public member function
<unordered_set>

std::unordered_set::count

size_type count ( const key_type& k ) const;
Count elements with a specific key
Searches the container for elements with a value of k and returns the number of elements found. Because unordered_set containers do not allow for duplicate values, this means that the function actually returns 1 if an element with that value exists in the container, and zero otherwise.

Parameters

k
Value of the elements to be counted.
Member type key_type is the type of the elements in the container. In unordered_set containers it is the same as value_type, defined as an alias of the class's first template parameter (Key).

Return value

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

Member type size_type is an unsigned integral type.

Example

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// unordered_set::count
#include <iostream>
#include <string>
#include <unordered_set>

int main ()
{
  std::unordered_set<std::string> myset = { "hat", "umbrella", "suit" };

  for (auto& x: {"hat","sunglasses","suit","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;
}


Output:
myset has hat
myset has no sunglasses
myset has suit
myset has no t-shirt

Complexity

Average case: constant.
Worst case: linear in container size.

Iterator validity

No changes.

See also

  • 9281021542 2018-02-20
  • 632231541 2018-02-20
  • 9751491540 2018-02-20
  • 8333621539 2018-02-20
  • 995001538 2018-02-20
  • 6477441537 2018-02-20
  • 511981536 2018-02-19
  • 2072881535 2018-02-19
  • 6024461534 2018-02-19
  • 7594061533 2018-02-19
  • 9311341532 2018-02-19
  • 4928331531 2018-02-19
  • 38561530 2018-02-19
  • 7776611529 2018-02-19
  • 3038041528 2018-02-19
  • 9566341527 2018-02-19
  • 3936031526 2018-02-19
  • 9531111525 2018-02-19
  • 291211524 2018-02-19
  • 8962001523 2018-02-19