From: Rob <robpilling@gmail.com>
To: musl@lists.openwall.com
Subject: Re: NULL
Date: Wed, 9 Jan 2013 22:17:28 +0000 [thread overview]
Message-ID: <20130109221728.GB17059@headless> (raw)
In-Reply-To: <20130109215327.GM4468@port70.net>
On Wed, Jan 09, 2013 at 10:53:27PM +0100, Szabolcs Nagy wrote:
> * Rob <robpilling@gmail.com> [2013-01-09 21:11:28 +0000]:
> > On Wed, Jan 09, 2013 at 10:36:30AM -0500, Rich Felker wrote:
> > > char s[1][1+(int)NULL];
> > > int i = 0;
> > > return sizeof s[i++], i;
> >
> > Magic... is `s' a VLA here? My mind is boggled because
> > __builtin_constant_p(1+(int)NULL) returns 1, and I can't think of any
> > reason why the sizeof is evaluated.
> >
> > Also, seeing that clang and tcc return 0 in all cases, is this a bug in
> > both of them?
>
> sizeof evaluates its argument if and only if it is a vla
> (c11 6.5.3.4p2)
>
> in c99 (and c11) vla is created if the size in the array
> declarator is not an "integer constant expression"
> (c11 6.7.6.2p4)
>
> eg '1 + (int)(void*)0' is not an integer constant expression
> because of the pointer cast, but '1 + (int)0' is
> (c11 6.6p6)
>
> hence sizeof s[i++] evaluates the argument if NULL has a pointer
> cast in it
Ah, thanks for the explanation.
next prev parent reply other threads:[~2013-01-09 22:17 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-09 11:02 NULL John Spencer
2013-01-09 12:18 ` NULL Szabolcs Nagy
2013-01-09 13:36 ` NULL John Spencer
2013-01-12 6:32 ` NULL Rob Landley
2013-01-12 6:46 ` NULL Rich Felker
2013-01-12 7:15 ` NULL Luca Barbato
2013-01-12 13:33 ` NULL Rich Felker
2013-01-12 11:39 ` NULL Jens Staal
2013-01-09 13:09 ` NULL croco
2013-01-09 13:47 ` NULL John Spencer
2013-01-09 14:49 ` NULL croco
2013-01-09 14:42 ` NULL Luca Barbato
2013-01-09 14:47 ` NULL Rich Felker
2013-01-09 15:03 ` NULL Luca Barbato
2013-01-09 15:18 ` NULL John Spencer
2013-01-09 15:36 ` NULL Rich Felker
2013-01-09 21:11 ` NULL Rob
2013-01-09 21:53 ` NULL Szabolcs Nagy
2013-01-09 22:17 ` Rob [this message]
2013-01-09 23:42 ` NULL Szabolcs Nagy
2013-01-12 6:56 ` NULL Rob Landley
2013-01-12 7:07 ` NULL Bobby Bingham
2013-01-12 13:31 ` NULL Rich Felker
2013-01-13 14:29 ` NULL Rob Landley
2013-01-13 14:56 ` NULL Luca Barbato
2013-01-13 16:29 ` NULL Rob Landley
2013-01-13 17:14 ` NULL Luca Barbato
2013-01-13 15:23 ` NULL Strake
2013-01-13 17:17 ` NULL Luca Barbato
2013-01-13 17:47 ` NULL Szabolcs Nagy
2013-01-13 19:46 ` NULL Rob Landley
2013-01-14 6:11 ` NULL Rich Felker
2013-01-14 8:45 ` musl as a framework to test applications' compatibility with POSIX (was: NULL) Vasily Kulikov
2013-01-14 14:03 ` Rich Felker
2013-01-14 14:30 ` Vasily Kulikov
2013-01-14 15:02 ` Szabolcs Nagy
2013-01-14 15:14 ` Rich Felker
2013-01-14 13:19 ` NULL Rob Landley
2013-01-12 5:56 ` NULL Rob Landley
2013-01-12 6:42 ` NULL Rich Felker
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