#include into multiple sources

[Kanner]

if i have a set of variables listed in an include file and I want to use them in multiple source files how do I need to structure the include file.

Currently I am using #include <MYFILE> statement in both .c files and i get linking errors stating that I have redefined. And if I only include in one source the other source is lacking the variables.

[Hammurabi]

Do not define variables in a header file.

Only define them in ONE source file, then in the header file put something like this:

extern int g_somevar;
extern int g_someothervar;

I prefixed it with g_ to indicate that it is global (and hopefully avoid name conflicts).

[Kanner]

Thank you. That all that was needed.

[Disch]

To avoid having to duplicate variable declarations (once in the header, once in a .cpp file), you can use a trick with macros:

// globals.cpp

#define GLOBAL
#include "globals.h"

 // -- can leave rest of file empty 

// globals.h

#ifndef GLOBAL
#define GLOBAL extern
#endif

GLOBAL int g_somevar;
GLOBAL int g_someothervar;

Though it's worth noting that globals should be avoided most of the time because they lead to sloppy, unorganized, hard to follow code that is not easily reusable.