How to have a set of structs in C++

Question

I have a struct which has a unique key. I want to insert instances of these structs into a set. I know that to do this the < operator has to be overloaded so that set can mak

Answer 1

This might help:

struct foo
{
  int key;
};

inline bool operator<(const foo& lhs, const foo& rhs)
{
  return lhs.key < rhs.key;
}

If you are using namespaces, it is a good practice to declare the operator<() function in the same namespace.

---

For the sake of completeness after your edit, and as other have pointed out, you are trying to add a foo* where a foo is expected.

If you really want to deal with pointers, you may wrap the foo* into a smart pointer class (auto_ptr, shared_ptr, ...).

But note that in both case, you loose the benefit of the overloaded operator< which operates on foo, not on foo*.