Question

I have classes A and B with both having their header files with include guards. One reads:

#ifndef A_H
#define A_H

#include "B.h"

class A
{
B b;
};

#endif

And the other one:

#ifndef B_H
#define B_H

#include "A.h"

class B
{
A a;
};

#endif

Now I test it with the following main.cpp:

#include "A.h"

int main()
{
        A a;
}

The compiling error is as follows:

# make main
g++     main.cpp   -o main
B.h:8: error: ‘A’ does not name a type

Is there any solution to this situation, other than using a pointer/reference and a forward declaration?

Answer 1

No, it’s not possible: one of them needs to be a pointer or a reference: because if A contains B, which contains A, which contains B, then you have infinite recursion and are trying to specify infinite sized object.