From: jxh AT cs DOT wustl DOT edu (James Hu)
Newsgroups: comp.os.msdos.djgpp,comp.lang.c
Subject: Re: Can't get external variables to work!??
Date: 7 Feb 1998 16:20:53 GMT
Organization: Washington University in St. Louis
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Message-ID: <slrn6dp2f4.j5q.jxh@lambada.cs.wustl.edu>
References: <34DC7457 DOT 6A0A7521 AT iafrica DOT com>
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To: djgpp AT delorie DOT com
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On Sat, 07 Feb 1998 16:48:55 +0200, Bruce Merry (the Almighty Cheese) <bmerry DOT nospam AT iafrica DOT com> wrote:
>c_types.h:
>typedef unsigned char byte;
>
>kbd.h:
>extern byte keys[128];
>
>program.c:
>#include "c_types.h"
>#include "kbd.h"
>/* stuff with the keys array */
>
>kbd.c:
>#include "c_types.h"
>static volatile byte keys[128];
>/* 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).

The problem is that in kbd.h you are declaring that there is some global
variable with external linkage named keys to be used, and program.c uses
this variable.  However, in kbd.c, you are have defined keys to be a
static variable, which implies that it does not have external linkage.
If you are counting on program.c being able to manipulate the variable
keys that is defined in kbd.c, there is no way of doing so.

Removing the keyword static from your definition of keys in kbd.c should
solve your problem, assuming that is the variable you intended program.c
to be able use.

This problem could have been diagnosed if you had #include'd kbd.h into
kbd.c.


-- 
James C. Hu <jxh AT cs DOT wustl DOT edu>       Computer Science Doctoral Student 
http://www.cs.wustl.edu/~jxh/        Washington University in Saint Louis
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