How can I use a struct as key in a std::map?

Question

I have the following code, but I get an error on on the last line:

struct coord { 
    int x, y; 

    bool operator=(const coord &o) {
        return x          


        

Answer 1

By far the simplest is to define a global "less than" operator for your struct in stead of as a member function.

std::map uses - by default - the 'lessthan' functor which, in turn, uses the global "operator<" defined for the key type of the map.

bool operator<(const coord& l, const coord& r) {
     return (l.x