shared global variables in C

Question

How can I create global variables that are shared in C? If I put it in a header file, then the linker complains that the variables are already defined. Is the only way to de

Answer 1

There is a cleaner way with just one header file so it is simpler to maintain. In the header with the global variables prefix each declaration with a keyword (I use common) then in just one source file include it like this

#define common
#include "globals.h"
#undef common

and any other source files like this

#define common extern
#include "globals.h"
#undef common

Just make sure you don't initialise any of the variables in the globals.h file or the linker will still complain as an initialised variable is not treated as external even with the extern keyword. The global.h file looks similar to this

#pragma once
common int globala;
common int globalb;
etc.

seems to work for any type of declaration. Don't use the common keyword on #define of course.