What is the best way to use two keys with a std::map?

Question

I have a std::map that I\'m using to store values for x and y coordinates. My data is very sparse, so I don\'t want to use arrays or vectors, which would result in

Answer 1

I usually solve this kind of problem like this:

struct Point {
    int x;
    int y;
};

inline bool operator<(const Point& p1, const Point& p2) {
    if (p1.x != p2.x) {
        return p1.x < p2.x;
    } else {
        return p1.y < p2.y;
    }
}