Question

Could a variable of Data be used as a map key?

struct Data {
Data(int X, int Y) {x=X; y=Y;}
int x; int y;
}

int main()
{
   std::map<Data, int> map_;
   map_.insert(std::make_pair(Data(1,2), 0)); //error inserting
}

Answer 1

Yes, but you either need to define operator< for the class type or use a custom comparison function for the std::map.

There is an example of using a custom comparison function in the STL documentation.