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

From: Jeff King <peff@peff.net>
Date: Jan 6, 2020, 21:30 UTC
Message-ID: <20200106213051.GD980197@coredump.intra.peff.net>
In-Reply-To: <CAN7CjDDBA0ZoCG9aaQf5rg3gxqny=EjR6v6jE1mnxvUJQSF_0Q@mail.gmail.com>

On Mon, Jan 06, 2020 at 10:15:53PM +0100, Miriam R. wrote:

Show 10 quoted lines

> 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.

Ref: http://c-faq.com/malloc/ptrafterfree.html

I'd probably leave it alone unless it is causing a problem (e.g., a static analyzer complaining).

-Peff