Is it possible to #Include in a "diamond inheritance" structure?

Question

I'm trying to make some project in C.

I would like to know if it is possible to make #include from the same file twice, in a way that recalls diamond heritage.

i.e.

Is it possible to #include "b.h" in a.c?

I get an error:

some_variable already defined in a.obj

Simple: don't *define* variables in headers, just *declare* them. — Paul R, Dec 18 '12 at 16:41
@PaulR how do you declare `int` in header without defining it? — SomeWittyUsername, Dec 18 '12 at 16:42

score 6 · Accepted Answer · answered Dec 18 '12 at 16:44

Simple: don't define variables in headers, just declare them:

Header:

// a.h

#ifndef A_H             // always use #include guards
#define A_H

extern int my_variable; // declare my_variable

...

#endif

Source file a.c:

// a.c

#include "a.h"

int my_variable;        // define my_variable

...

Source file b.c:

// a.c

#include "a.h"
#include "b.h"

...

As others have mentioned, #include guards are useful, and a good habit to get into, but they are probably not the solution for this specific problem.

I already use the "#include guards", It doesn't help, I'll try your solution — hudac, Dec 18 '12 at 16:51

888 · Answer 2 · 2013-01-15T14:34:18.317

2

You have to declare extern the variables in a.h, then modify your header a.h in the following way:

 #ifndef a_h
 #define a_h

   //your a.h 

 #endif

edited Jan 15 '13 at 14:34

answered Dec 18 '12 at 16:44

888

2 Answers2