How to have classes reference each other

[roblf]

My project currently does not build, and I believe the reason is this:

Class A has a local variable which is a pointer to Class B. Naturally I must #include "classB.h" in class A to declare this variable. However, Class B has a constructor which has a Class A pointer passed to it, so to declare this method prototype it must #include "classA.h". Now the code will not compile, since they both include each other and the constructor definition in Class B will occur before class A has been declared, so I get the error:

"error: expected ‘;’ before ‘*’ token"

on the line which declares the Class B pointer.

What is the appropriate way to get around this issue?

Thanks in advance.

[jsmith]

Your assessment of the problem is correct, however you don't have to include classB.h in classA.h or vice versa.

Use forward declarations:

File: classA.h:

#ifndef CLASSA_H
#define CLASSA_H

class B;   // forward declaration

class A {
   B* pB;
};

#endif 

When you only refer to a type by reference or by pointer, you do not need to include it's header file; rather you can forward declare.