How to create a std::set with custom comparator in C++?

Question

How do I create a set of pairs, the elements of which (the pairs) are sorted with a custom bool function? I write

set ,compare> my         


        

Answer 1

Method 1: use functor

Write a class that overloads the operator()so it can be called like a function:

struct compare {
    bool operator() (const pair &lhs, const pair &rhs) const{
         return (lhs.second-lhs.first > rhs.second-rhs.first);
    }
};

Then, you can use the class name as the type parameter

set, compare> myset;

Method 2: use function pointer

Assuming compare is the function you want to use:

set, bool(*)(const pair &lhs, 
                           const pair &rhs)
   > myset(&compare);