C++: Has Not Been Declared

Question

I have seen this type of error everywhere and, although I have looked at the answers, none seem to help.

I get the following error with the following piece of code:<

Answer 1

Replace the include with a forward declaration:

//B.h
class A;
class B{
    public:
         static bool doX(A *a);
};

Include files only when you have to.

Also, use include guards. This will prevent other nasty issues like re-definitions & such.

Answer 2

If you have two headers including each other you end up with a circular dependency, and due to the way the preprocessor works it means one will be defined before the other.

To fix, I would avoid including A.h in B.h, and just forward declare instead:

class A;
class B{
    public:
         static bool doX(A *a);
};

You can then include A.h in B.cpp