STL set custom sort

Question

I was trying to resort a set when i realised that it was impossible to resort a set and i had to create a new set and have a custom sort function to resort it . I researched onl

Answer 1

It's usually better to define a functor class to specify the ordering, rather than a function; that way, you can specify it as a template parameter:

struct p2d_sortby_y {
    bool operator()(Point2D x, Point2D y) {return whatever;}
};

This has to take its arguments by value or const reference (not non-const reference, as yours does) to be used on the constant set members.

You can't directly initialise the new set from a different type of set, but you can initialise it from its range:

set p2d_set2(p2d_set.begin(), p2d_set.end());