Question

I have a bit of problem with this. I have a class A which instantiates an object of B and then B which instantiates an object of A. Is this at all possible? I tried adding this in the headers of each

#ifndef A
#define A
  class a...
#endif

but if keeps me in an infinite header loop which it reaches the maximum header includes, so obviously one is calling the other and the other is calling that one. Is there any way to achieve this?

edit: Okay this seems like a good answer but now A complains that B doesn’t have a Constructor despite the fact that it definitely has a constructor. I can’t figure that one out.

Answer 1

You can forward declare the classes, for example:

A.h:

class B;

class A
{
    B* a_;
};

B.h:

class A;

class B
{
    A* a_;
};

In your source files where you actually use the classes (that is, create them, destroy them, use their members, etc.), you will need to include both headers so that their definitions are available:

#include "A.h"
#include "B.h"