Question

I’m a bit confused about using STL set::find() for a set of my own defined class objects.

My class contains more than two items (3/4/5 etc.), so how can I overload less operator?

I tried for 3 variable, which is as follows and working fine:

return( (a1.i < a2.i) ||
    (!(a1.i > a2.i) && (a1.f < a2.f)) ||
    (!(a1.i > a2.i) && !(a1.f > a2.f) && (a1.c < a2.c)));

where, a1, and a2 are class objects and (i, f and c are class members).

Now I want to generalize this for n members, but my find() does not always work.

I’ve been looking through STL’s detailed documentation, trying to learn how set::find() is implemented, and why it needs less (<) operator overloading.

I referred to sgi and msdn documentation, but I could not find much about implementation details of set::find() there, either.

What am I doing wrong in my set::find() implementation?

Answer 1

You have to define a strict ordering of your objects. So if your object is made up of n members a_1 .. a_n which all have a strict ordering themselves, what you can do is:

bool operator< (const TYPE &rhs) {
  if (a_1 < rhs.a_1) return true; else if (a_1 > rhs.a_1) return false;
  if (a_2 < rhs.a_2) return true; else if (a_2 > rhs.a_2) return false;
  ...
  if (a_n < rhs.a_n) return true;
  return false;
}

Edit:
If either boost or C++11 is an option for you, you should really go with the std::tie/boost::tie method Luc Danton suggests in his answer. It’s much cleaner.