From: Jeff King <peff@peff.net>
To: Mike Hommey <mh@glandium.org>
Cc: "Junio C Hamano" <gitster@pobox.com>,
"Git List" <git@vger.kernel.org>, "René Scharfe" <l.s.r@web.de>,
"Andreas Schwab" <schwab@linux-m68k.org>,
"Johannes Sixt" <j6t@kdbg.org>
Subject: Re: [PATCH] strbuf: use designated initializers in STRBUF_INIT
Date: Sat, 15 Jul 2017 07:08:39 -0400 [thread overview]
Message-ID: <20170715110839.hefdnf4eqhdwboxq@sigill.intra.peff.net> (raw)
In-Reply-To: <20170714224309.7p4a4vuuv3k2cdjg@glandium.org>
On Sat, Jul 15, 2017 at 07:43:09AM +0900, Mike Hommey wrote:
> > - There were occasional cases where we wished if variable-length
> > arrays, flexible array members and variadic macros were available
> > in our codebase during the course of this project. We would
> > probably want to add a similar test baloon patch for each of
> > them to this series that is currently two-patch long.
>
> FWIW, variadic macros have subtle implementation differences that can
> cause problems.
> For instance, MSVC only supports ##__VA_ARGS__ by way of
> ignoring ## somehow, but has the default behavior of dropping the comma
> when __VA_ARGS__ is empty, which means , __VA_ARGS__ *without* ## has a
> different behavior.
> See also https://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement
When there's any other non-optional argument, you can work around this
by just lumping that argument in with the varargs. So don't do:
#define FOO(fmt, ...) printf(fmt, __VA_ARGS__)
which fails when the format has no placeholders. Instead do:
#define FOO(...) printf(__VA_ARGS__)
That limits your interface for variadic macros, but in practice it
doesn't usually come up (there are also disgusting macro tricks you can
do to cover the true 0-arg case portably, but we haven't had to turn to
them yet).
-Peff
next prev parent reply other threads:[~2017-07-15 11:08 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-10 7:03 [PATCH] strbuf: use designated initializers in STRBUF_INIT Jeff King
2017-07-10 14:57 ` Ben Peart
2017-07-10 16:04 ` Jeff King
2017-07-10 17:57 ` Ben Peart
2017-07-11 5:01 ` Mike Hommey
2017-07-11 15:31 ` Junio C Hamano
2017-07-12 19:12 ` Ævar Arnfjörð Bjarmason
2017-07-12 21:08 ` Junio C Hamano
2017-07-13 22:24 ` Johannes Sixt
2017-07-10 16:44 ` Junio C Hamano
2017-07-10 17:33 ` Stefan Beller
2017-07-10 21:46 ` Junio C Hamano
2017-07-10 17:10 ` Andreas Schwab
2017-07-10 19:57 ` Johannes Sixt
2017-07-10 20:38 ` Junio C Hamano
2017-07-10 21:11 ` Johannes Sixt
2017-07-10 21:38 ` Junio C Hamano
2017-07-14 16:11 ` Junio C Hamano
2017-07-14 17:13 ` Stefan Beller
2017-07-14 17:36 ` Jeff King
2017-07-14 18:48 ` Junio C Hamano
2017-07-14 19:16 ` Junio C Hamano
2017-07-19 18:19 ` [PATCH] objects: scope count variable to loop Stefan Beller
2017-07-19 18:23 ` Brandon Williams
2017-07-24 17:08 ` Jeff King
2017-07-24 17:12 ` Stefan Beller
2017-07-24 18:05 ` Jeff King
2017-07-14 19:28 ` [PATCH] strbuf: use designated initializers in STRBUF_INIT Ævar Arnfjörð Bjarmason
2017-07-14 22:26 ` Junio C Hamano
2017-07-14 22:43 ` Mike Hommey
2017-07-15 11:08 ` Jeff King [this message]
2017-07-11 4:38 ` Jeff King
2017-07-11 0:05 ` brian m. carlson
2017-07-11 0:07 ` Stefan Beller
2017-07-11 0:10 ` brian m. carlson
2017-07-11 5:24 ` Johannes Sixt
2017-07-12 1:26 ` brian m. carlson
2017-07-12 18:25 ` Johannes Sixt
2017-07-10 22:41 ` Brandon Williams
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