Question

I am curious about a scenario set up like the following example:

Here is code that would be placed in a file called Header1.h:

#ifndef HEADER1_H
#define HEADER1_H

#include "Header2.h"

class Class1
{
 Class2 class2Instance;
};

#endif

Here is code that would be placed in a file called Header2.h:

#ifndef HEADER2_H
#define HEADER2_H

#include "Header1.h"

class Class2
{
 Class1 class1Instance;
};

#endif

I get error messages when I do this (because of the includes I assume), but it feels like I would need to do this in order to include each of the objects in the separate classes. Can anyone help me accomplish this, what am I doing wrong?

Answer 1

The problem is that the size of Class1 depends on Class2, and vice-versa. Therefore, there’s no way to calculate the size for either one. Forward-declare one of the classes, and change one of the attributes to be a pointer or reference:

#ifndef HEADER2_H
#define HEADER2_H

class Class1;
class Class2
{
 Class1 *class1Instance;
 // or
 Class1 &class1Instance;
};

#endif