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From: Robby on 18 Dec 2009 13:07
Hello,

I have asked this question in a previous post. I don't mean to double post,
but I would simply like to ask the same question in a more direct manner.

Please consider these .c modules:

=====================KERNEL.h
extern long MQ[];

=====================KERNEL.c
long MQ[10] = {1,2,3,4,5,6,7,8,9,0}; // <<< at top of a particular .c
file!

=====================API.c
#include KERNEL.h // <<< include KERNEL.h header in all .c files that
need MQ[]

void API_InsertMessage(enum enumKM m)
{ MQ[0] = m; }
===========================

Objective:
The data in the MQ array has to be accessible and available in many
functions of several .c files, and therefore should appear to have global
scope.

Resolution:
As shown in code above, I declared an array as "extern" and then defined it
in one .c file and where ever other .c files require access to MQ[], I have
to include the KERNEL.h file. Is this an okay practice to do with all other
global variables, arrays and arrays of structures?

P.S. I am only asking this to assure that I apply the same coding habits for
the rest of my global variables.

In all sincereity, thanks all for any feedback!

--
Best regards
Roberto
From: David Lowndes on 18 Dec 2009 13:34
>As shown in code above, I declared an array as "extern" and then defined it
>in one .c file and where ever other .c files require access to MQ[], I have
>to include the KERNEL.h file. Is this an okay practice to do with all other
>global variables, arrays and arrays of structures?

Yes.

Dave
From: Robby on 18 Dec 2009 14:34
Thank you Dave!

--
Best regards
Roberto


"David Lowndes" wrote:

> >As shown in code above, I declared an array as "extern" and then defined it
> >in one .c file and where ever other .c files require access to MQ[], I have
> >to include the KERNEL.h file. Is this an okay practice to do with all other
> >global variables, arrays and arrays of structures?
>
> Yes.
>
> Dave
> .
>
From: mzdude on 18 Dec 2009 16:54
On Dec 18, 1:07 pm, Robby <Ro...(a)discussions.microsoft.com> wrote:
<snip>
> Resolution:
> As shown in code above, I declared an array as "extern" and then defined it
> in one .c file and where ever other .c files require access to MQ[], I have
> to include the KERNEL.h file. Is this an okay practice to do with all other
> global variables, arrays and arrays of structures?
>
> P.S. I am only asking this to assure that I apply the same coding habits for
> the rest of my global variables.
>

Having been bitten by global vars more than once in my life time, I
would do something like

=== Kernal.h =====
long GetMessage(int msgIndex );
void SetMessage(int msgIndex, long message );

==== Kernal.c ===
static long MQ[10] = {1,2,3,4,5,6,7,8,9,0};

long GetMessage(int msgIndex)
{ return MQ[msgIndex]; } // could add range check to index

void SetMessage(int msgIndex, long message)
{ MQ[msgIndex] = message; }


Just my preference.

==== Api.c ====
#include "Kernal.h"

void API_InsertMessage(enum enumKM m)
{ SetMessage(0, m); }


Now if you ever have to track down message changes, you
have a single function in Kernal.c to set break points in,
or add logging functions too.
From: Barry Schwarz on 19 Dec 2009 03:58
On Fri, 18 Dec 2009 18:34:12 +0000, David Lowndes
<DavidL(a)example.invalid> wrote:

>>As shown in code above, I declared an array as "extern" and then defined it
>>in one .c file and where ever other .c files require access to MQ[], I have
>>to include the KERNEL.h file. Is this an okay practice to do with all other
>>global variables, arrays and arrays of structures?
>
>Yes.

While this is obviously the right (tm) way to define a global variable
exactly once and declare it extern everywhere it is needed, it begs
the question of whether global variables are the right choice. Since
they have a tendency to confound debugging, there is a school of
thought that strongly recommends passing the array as an argument to
those functions that need it.

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