public member function
<unordered_map>

std::unordered_map::count

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

Parameters

k
Key value to be searched for.
Member type key_type is the type of the keys for the elements in the container, defined in unordered_map as an alias of its first template parameter (Key).

Return value

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

Member type size_type is an unsigned integral type.

Example

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

int main ()
{
  std::unordered_map<std::string,double> mymap = {
     {"Burger",2.99},
     {"Fries",1.99},
     {"Soda",1.50} };

  for (auto& x: {"Burger","Pizza","Salad","Soda"}) {
    if (mymap.count(x)>0)
      std::cout << "mymap has " << x << std::endl;
    else
      std::cout << "mymap has no " << x << std::endl;
  }

  return 0;
}


Output:
mymap has Burger
mymap has no Pizza
mymap has no Salad
mymap has Soda

Complexity

Average case: linear in the number of elements counted.
Worst case: linear in container size.

Iterator validity

No changes.

See also

  • 9316991614 2018-02-25
  • 191841613 2018-02-25
  • 16411612 2018-02-25
  • 6081981611 2018-02-25
  • 1784561610 2018-02-25
  • 4651609 2018-02-25
  • 9348111608 2018-02-25
  • 2513771607 2018-02-25
  • 6478461606 2018-02-24
  • 4985791605 2018-02-24
  • 5637141604 2018-02-24
  • 282181603 2018-02-24
  • 6217941602 2018-02-24
  • 5076141601 2018-02-24
  • 714281600 2018-02-24
  • 6607141599 2018-02-24
  • 949041598 2018-02-24
  • 6809961597 2018-02-24
  • 671871596 2018-02-24
  • 7107821595 2018-02-24