Re: [Outreachy] Return value before or after free()?

From: Andreas Schwab <schwab@linux-m68k.org>
Date: Jan 6, 2020, 23:34 UTC
Message-ID: <87imlo6twj.fsf@igel.home>
In-Reply-To: <20200106213051.GD980197@coredump.intra.peff.net>

On Jan 06 2020, Jeff King wrote:

Show 16 quoted lines

> On Mon, Jan 06, 2020 at 10:15:53PM +0100, Miriam R. wrote:
>
>> in run-command.c file `exists_in_PATH()` function does this:
>> 
>> static int exists_in_PATH(const char *file)
>> {
>> char *r = locate_in_PATH(file);
>> free(r);
>> return r != NULL;
>> }
>> 
>> I wonder if it is correct to do return r != NULL; after free(r);
>
> It is technically undefined behavior according to the C standard, but I
> think it would be hard to find an implementation where it was not
> perfectly fine in practice.

Compilers get constantly better at exploiting undefined behaviour, so I would not count on it.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."