C++ #include guards

Question

SOLVED

What really helped me was that I could #include headers in the .cpp file with out causing the redefined error.

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I\'m new to C++ but I have some p

Answer 1

Firstly you need include guards on gameobject too, but that's not the real problem here

If something else includes physics.h first, physics.h includes gameobject.h, you get something like this:

class GameObject {
...
};

#include physics.h

class Physics {
...
};

and the #include physics.h gets discarded because of the include guards, and you end up with a declaration of GameObject before the declaration of Physics.

But that's a problem if you want GameObject to have a pointer to a Physics, because for htat physics would have to be declared first.

To resolve the cycle, you can forward-declare a class instead, but only if you are just using it as a pointer or a reference in the declaration following, i.e.:

#ifndef PHYSICS_H
#define PHYSICS_H

//  no need for this now #include "GameObject.h"

#include 

class GameObject;

class Physics
{
private:
    list objects;
    list::iterator i;
public:
    void ApplyPhysics(GameObject*);
    Vector2X CheckCollisions(Vector2X, GameObject*);
};

#endif // PHYSICS_H