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Message-ID: <CAFNaaxQKNXK0MDV1n73AGFQGR6VZkx-Lvk7NCEuMyzFeazEG1A@mail.gmail.com>
Date: Sat, 12 Jan 2013 01:07:46 -0600
From: Bobby Bingham <uhmmmm@...il.com>
To: musl@...ts.openwall.com
Subject: Re: NULL
On Sat, Jan 12, 2013 at 12:56 AM, Rob Landley <rob@...dley.net> wrote:
>> int null_is_ptr_type()
>> {
>> char s[1][1+(int)NULL];
>> int i = 0;
>> return sizeof s[i++], i;
>> }
>
>
> (int)NULL is 0 according to C99 so the NULL in there has no effect. And
> referring to "i++" and "i" in the same statement is explicitly undefined
> behavior (comma is not a sequence point, the compiler is free to evaluate
> those in any order and different optimization flags _will_ change that
> order; I got bit by that many moons ago).
>
>From c99 section 6.5.17 Comma operator:
"The left operand of a comma operator is evaluated as a void
expression; there is a sequence point after its evaluation. Then the
right operand is evaluated; the result has its type and value"
--
Bobby Bingham
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