error: expected class-name before ‘{’ token

Question

I know there are a couple of similar questions(circular include) out stackoverflow and other websites. But I still can\'t figure it out and no solutions pop out. So I would

Answer 1

If you forward-declare Flight and Landing in Event.h, then you should be fixed.

Remember to #include "Flight.h" and #include "Landing.h" in your implementation file for Event.

The general rule of thumb is: if you derive from it, or compose from it, or use it by value, the compiler must know its full definition at the time of declaration. If you compose from a pointer-to-it, the compiler will know how big a pointer is. Similarly, if you pass a reference to it, the compiler will know how big the reference is, too.