c++ less operator overload, which way to use?

Question

For example: in a C++ header file, if I defined a struct Record and I would like to use it for possible sorting so that I want to overload the less operator

Answer 1

The best way to define the less operator is:

struct Record{
    (...)
    const bool operator < ( const Record &r ) const{
        return ( num < r.num );
    }
};