Listing 2. Global variables and functions are
declared in xr.h.

code:
#ifdef XR_CB_C
GtkWidget *XR_Msg_Window = NULL;
GtkWidget *XR_Msg = NULL;
void XRUMsg();
void XRUInit();
#else
extern GtkWidget *XR_Msg_Window;
extern GtkWidget *XR_Msg;
extern void XRUMsg();
extern void XRUInit();
#endif