public member function
<unordered_map>
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.
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_multimap as an alias of its first template parameter (Key).
Return value
The number of elements in the container with a key equivalent to k.
Member type size_type is an unsigned integral type.
Example
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// unordered_multimap::count
#include <iostream>
#include <string>
#include <unordered_map>
int main ()
{
std::unordered_multimap<std::string,std::string> myumm = {
{"orange","FL"},
{"strawberry","LA"},
{"strawberry","OK"},
{"pumpkin","NH"} };
for (auto& x: {"orange","lemon","strawberry"}) {
std::cout << x << ": " << myumm.count(x) << " entries.\n";
}
return 0;
}
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Output:
orange: 1 entries.
lemon: 0 entries.
strawberry: 2 entries.
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Complexity
Average case: linear in the number of elements counted.
Worst case: linear in container size.
Iterator validity
No changes.