GNU bug report logs - #24248
[patch] avoid duplicate definition of global variable presume_output_tty

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Message #10 received at 24248-done <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: Hanno Böck <hanno <at> hboeck.de>
Cc: 24248-done <at> debbugs.gnu.org
Subject: Re: [bug-diffutils] bug#24248: [patch] avoid duplicate definition of
 global variable presume_output_tty
Date: Tue, 16 Aug 2016 22:09:18 -0700

[Message part 1 (text/plain, inline)]

On Tue, Aug 16, 2016 at 6:17 PM, Hanno Böck <hanno <at> hboeck.de> wrote:
> Hi,
>
> The variable presume_output_tty is defined both in the diff.h header
> and the file util.c (which includes diff.h).
>
> The diff.h file makes sure that the variable is declared as external
> except when it's included by the main program diff.c. But as it's also
> declared in util.c we end up having two non-external declarations of it.
>
> Traditionally gcc has allowed this behavior, which is probably the
> reason it has not been spottet before, but it's not correct C. One can
> get a more strict behavior here by passing -fno-common to the CFLAGS and
> LDFLAGS and then linking will fail.
>
> The solution is simple: Remove the superfluous declaration in util.c,
> see attached patch. Please apply.

Good catch. Thank you!
I will look into adding -fno-common when it is accepted.
Here's the patch I expect to push soon:

[duplicate-defn-of-presume_output_tty.diff (text/plain, attachment)]

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