Question

When I want to use STL sets to store custom objects in C++,There are many people says:you should overload < operator,but if I want use find() method, I think it may use == operator to acheive that.Can anyone give me some pointers?

Answer 1

The Standard Library set::find uses equivalence instead of equality to find values. You don’t need to provide operator ==, just operator < (or whatever comparison operator you specified for set, std::less being the default).

If you are wondering how your element would be found, then assuming the default ordering find(x) would return the element e for which:

!( x < e || e < x )