Circular headerfile inclusion problem

[xoinki]

hi all,

I have 3 classes. class A, class B, and class C, class D, defined in 4 files A.cpp, B.cpp, C.cpp, D.cpp
inheritence hierarchy is as follows.
A--> B --> C
|
|
V
D
i.e, A is inherited by B which is inherited by C and D.
then, A and B has a virtual function test() overridden in C and D.
and I need to use dynamic binding as follows..

//this would be a member function of A
bool A::SomeFunc()
{
A * var;
if(some condition)
    var = new C();
else
    var = new D();
..
..
..
return TRUE;
}
 

so problem is..
A needs C and D.
C and D needs B.
and B needs A.
so there is a circular inclusion.
becuase of which base classes inherited are not recognised.
can anybody suggest a solution? is this a common problem?

waiting for your reply,
Xoinki

[Banfa]

This should not be a problem as long as bool A::SomeFunc() is defined in a CPP file and not a header file.

It is just a matter of including the headers in the right order at the top of the A.CPP file, probably

#include "A.h"
#include "B.h"
#include "C.h"
#include "D.h"
 

This is more of a problem if there are 2 classes X and Y each of which has methods that take a pointer or reference to the other class. In this case you need to know and X in Y.H and Y in X.H which does create a header file interdependency .

The way round this is a forward declaration, this looks something like

class X;
 

This tells the compiler "at some point in the future I am going to declare a class named X" and provides the compiler with enough information to create pointers and references to the class (but not to access the class members).