From: cwr AT cts DOT com (Will Rose)
Newsgroups: comp.os.msdos.djgpp,comp.lang.c
Subject: Re: Can't get external variables to work!??
Followup-To: comp.os.msdos.djgpp,comp.lang.c
Date: 7 Feb 1998 16:05:11 GMT
Organization: CTS Network Services (CTSNET), San Diego, CA
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Bruce Merry (the Almighty Cheese) (bmerry DOT nospam AT iafrica DOT com) wrote:
: Hi

: I've been using C and C++ for quite a while now, but up to now I've not
: needed to share a variable between source files. What I am trying at the
: moment is basically (with other stuff removed):

There are are several ways around this.  One is:

: c_types.h:
: #ifndef __my_c_types_h
: #define __my_c_types_h
: typedef unsigned char byte;
: #endif

: kbd.h:
: #ifndef __my_kbd_h
: #define __my_kbd_h
#ifndef EXTERN
#define EXTERN extern
#endif
: #include "c_types.h"
EXTERN byte keys[128];
: #endif

: program.c:
#define EXTERN	/* defined in one source file only */
: #include "c_types.h"
: #include "kbd.h"
: /* stuff with the keys array */

: kbd.c:
: #include "c_types.h"
: static volatile byte keys[128];
/* I'm lost here; why have you declared keys[] static if you
 * want them to be accessible from other compilation units?
 * And why a volatile array?  volatile is mostly used for
 * i/o addresses, to avoid unwanted optimisation.  keys[]
 * is just storage (AFAIK) for data once it's been read.
 * Omit this line and include kbd.h to handle the declaration.
 * You also need to decide whether to include all headers by
 * name in source files, or include headers within headers, and
 * then stick to one convention to avoid confusion.
 */
: /* code for keyboard handling */

: Basicly, all the source files compile into objects fine, but at link
: time the error 'undefined reference to keys' multiple times. What am I
: doing wrong (I'm using DJGPP 2, BTW).

: Thanks in advance
: Bruce


Will
cwr AT crash DOT cts DOT com