I have a struct:

struct Coordinate {
 double x, y, z;
};

There is no any operator definition for it.

 

I want to sort a array of this struct with 3 elements by comparing the Z value, so:

Coordinate coords[3];

.......

std::sort(coords, coords+3, _1 < _2);

What should I write to replace "_1 < _2" here? How can I reference the Z member of _1 and _2?

I hope I can sort this array without defining any new function.