From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: git@vger.kernel.org, Denton Liu <liu.denton@gmail.com>
Subject: Re: [RFC] CodingGuidelines: mark external declarations with "extern"
Date: Fri, 09 Oct 2020 13:33:39 -0700 [thread overview]
Message-ID: <xmqqpn5rrvfg.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <20201009195701.GA967869@coredump.intra.peff.net> (Jeff King's message of "Fri, 9 Oct 2020 15:57:01 -0400")
Jeff King <peff@peff.net> writes:
> The argument for including it is less clear to me. You say below:
>
>> [...]By doing so, we would also prevent a
>> mistake of not writing "extern" when we need to (i.e. decls of data
>> items, that are not functions) when less experienced developers try
>> to mimic how the existing surrounding declarations are written.
>
> but to my recollection that has not been a big problem. And it's one
> that's usually easily caught by the compiler. A missing "extern" on a
> variable will usually get you a multiple-definition warning at
> link-time (if you manage to also omit the actual definition you won't
> see that, though "make sparse" will warn that your variable ought to be
> static).
Not really, that is where the "common" extension comes in, to help
us with it hurt others without it, unknowingly X-<.
$ cat >a.c <<\EOF
#include <stdio.h>
#include "c.h"
int common = 47;
int main(int ac, char **av)
{
printf("%d\n", common + other);
return 0;
}
EOF
$ cat >b.c <<\EOF
#include "c.h"
int other = 22;
EOF
$ cat >c.h <<\EOF
int common;
int other;
EOF
$ gcc -Wall -o c a.c b.c; ./c
59
And I have a strong preference, after thinking about it, to have
"extern" in front in the declarations. It gives another clue for
patterns I feed to "git grep" to latch onto, and help my eyes to
scan and tell decls and defns apart in the output. The benefit
alone is worth the extra 7 columns in front spent, which you call
"clutter".
> IMHO the real problem here is that C's syntax for returning a function
> pointer is so horrendous. How about this (on top of your earlier patch
> to drop the extern from that declaration)?
In general, I like a typedef for callback function that shortens the
decl of a function that takes such a callback, so I think
> +void set_error_routine(report_fn routine);
> +void set_warn_routine(report_fn routine);
> +report_fn get_error_routine(void);
> +report_fn get_warn_routine(void);
these are good, but they are better with "extern" in front in a
header file to make it clear they are declarations and not
definitions when they appear in "git grep" output.
next prev parent reply other threads:[~2020-10-09 20:33 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-08 15:27 [PATCH] clean up extern decl of functions Junio C Hamano
2020-10-09 1:55 ` Denton Liu
2020-10-09 2:47 ` Junio C Hamano
2020-10-09 19:26 ` Junio C Hamano
2020-10-09 19:27 ` [RFC] CodingGuidelines: mark external declarations with "extern" Junio C Hamano
2020-10-09 19:57 ` Jeff King
2020-10-09 20:33 ` Junio C Hamano [this message]
2020-10-09 23:00 ` Denton Liu
2020-10-09 23:05 ` Junio C Hamano
2020-10-10 0:37 ` Đoàn Trần Công Danh
2020-10-15 1:36 ` Jeff King
2020-10-15 17:15 ` Junio C Hamano
2020-10-15 19:28 ` Jeff King
2020-10-15 19:30 ` [PATCH v2 1/2] usage: define a type for a reporting function Jeff King
2020-10-15 19:30 ` [PATCH v2 2/2] config.mak.dev: build with -fno-common Jeff King
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