public member function
<unordered_set>
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;
}
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Output:
myset has hat
myset has no sunglasses
myset has suit
myset has no t-shirt
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Complexity
Average case: constant.
Worst case: linear in container size.
Iterator validity
No changes.