Question

I have a simple Position struct:

struct Position
{
    int x;
    int y;
};

I also have a list of Positions:

std::list<Position> positons;

I’m trying to sort the list using list::sort() and need to define operator< for Positions objects. I tried keeping it simple creating something like:

bool operator<(const Position& one, const Position& two)
{
    return one.x < two.x && one.y < two.y;
}

But that doesn’t work. How do I determine that one class/struct object as a whole is less than another? How would I do it for my Position struct?

EDIT When I call positions.sort(), I get a debug assertion failed which says:
Expression: invalid operator<

Answer 1

You can sort by x and then by y. Also define it as free function:

bool function(const Position& one, const Position& two)
{
    return one.x < two.x || (one.x == two.x && one.y < two.y);
}

Or as operator:

bool operator<(const Position& other)const
{
    return x < other.x || (x == other.x && y < other.y);
}