1) Checks if there is an element with key equivalent tokey in the container.

2) Checks if there is an element with key that compares equivalent tox.

This overload participates in overload resolution only ifHash andKeyEqual are bothtransparent. This assumes that suchHash is callable with bothK andKey type, and that theKeyEqual is transparent, which, together, allows calling this function without constructing an instance ofKey.

#include <iostream>#include <unordered_map> int main(){std::unordered_multimap<int,char> example{{1,'a'},{2,'b'}}; for(int x:{2,5})if(example.contains(x))std::cout<< x<<": Found\n";elsestd::cout<< x<<": Not found\n";}

2: Found5: Not found