How to handle cyclic dependencies

Asked May 15 '15 at 14:22

Active May 18 '15 at 08:25

Viewed 50 times

I'm having some trouble with cyclic dependencies. Imagine the following sample classes:

A class A with instance variables of types C and D and a method that uses these 2 types inside plus another type D:

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

class A {

private:
    B b;
    C c;

    void foo(D d);
};

A class B that depends on C:

#include "C.h"

class C;

class B {

private:
    C c;

    //some methods
};

A class C that uses methods of class D:

#include "D.h"

class D;

class C {

private:
    double x;

    void bar(D d);
};

A class D that has methods that use variables of the type B and C:

#include "B.h"
#include "C.h"

class B;
class C;

class D {

private:
    int i;

    void foo2(B b);
    void bar2(C c);
};

The error I'm getting is:

B.h:8:2 error: ‘C’ does not name a type

How can I solve this problem with cyclic dependencies?

Thanks

Edit: Updated class B:

#include "C.h"

class C;

class B {

private:
    C* c;

    B (B b) {*c = *(b.c);} //copy constructor
    //some methods
};

edited May 18 '15 at 08:25

asked May 15 '15 at 14:22

fc67

1

If you need a variable of an incomplete type it needs to be a reference or a pointer. – NathanOliver May 15 '15 at 14:24
1

Don't `#include` what you don't need. Parameters and return values do not need the definition of a type, only its declaration. – Angew is no longer proud of SO May 15 '15 at 14:25
With correct forward declaration: https://ideone.com/GlaaWT – Jarod42 May 15 '15 at 14:31
The tricky part is that you take argument by value. but the argument can even be forward declared; argument definition should be known at call site (and probably also for the function definition). – Jarod42 May 15 '15 at 14:35
@Jarod42 I tried that and I still get the same error – fc67 May 15 '15 at 14:42
@fc67: I provided an ideone link which works with one unique file (with comment to split in different files) – Jarod42 May 15 '15 at 15:00
@NathanOliver I changed the variable C c in the class B to C* c and C& c and on both I get the same error because there are some operators from class C that I need to use – fc67 May 16 '15 at 11:48
@fc67 then re edit your post with the code as it is now and the errors you are getting – NathanOliver May 16 '15 at 13:58
@NathanOliver I edited the post with the updated code – fc67 May 18 '15 at 08:26

0 Answers0