Question

I have 2 header files that contain 2 classes. Each class is dependent on other, like so:

// class1.h

#include "class2.h"

class ClassOne {
    ClassTwo* c2;
};

---

// class2.h

#include "class1.h"

class ClassTwo {
    ClassOne* c1;
};

I expected the code not to compile, so I added a forward declaration to one of the headers:

// class1.h

#include "class2.h"

class ClassTwo;

class ClassOne {
    ClassTwo* c2;
};

But sadly that isn’t working, either. I keep getting compiler errors for “use of undefined type ‘ClassTwo'”.

I know I can just combine them into one header file and they will work, but in reality they are both really big classes and I really would prefer they have their own header file for organization purposes.

Is there a way to get around this?

Thanks,
Alex

Answer 1

You added the forward declaration but didn’t remove the include. Do that and you’re golden.

Actually, remove both includes, and replace them with forward declarations.

// class1.h

class ClassTwo;

class ClassOne {
    ClassTwo* c2;
};


// class2.h

class ClassOne;

class ClassTwo {
    ClassOne* c1;
};

Note that cases where circular dependencies are actually required are few and far apart, so at least review the design.