free() and implicit conversion to a function pointer
Corinna Vinschen
corinna-cygwin@cygwin.com
Fri Mar 17 08:30:00 GMT 2017
On Mar 17 00:49, Hans-Bernhard Bröker wrote:
> Am 16.03.2017 um 22:46 schrieb L A Walsh:
> > Going by subj and talk below, this is a bit confusing...
> >
> > But it looks like you are testing 'free' for a value?
>
> Not really. The idea is to test free for _exixtence_. Which only makes
> sense in case of weak symbol support getting involved. In other situations,
> there could not possibly be a need for a run-time if() test, because surely
> the code could know at build time whether free() exists or not.
>
> > Isn't standard 'free' declared to take 1 arg and
> > return void?
>
> Yes. But since the code in question doesn't actually _call_ free, that's
> both irrelevant.
>
> > If you aren't talking standard 'free()', then
> > nevermind...
>
> We are talking standard free. More to the point, we're discussing newlib,
> the package that actually implements free() for cygwin.
>
> > > The only code that might actually be a slight bit better than the given
> > >
> > > if (! free)
> > >
> > > would be
> > >
> > > if (0 != free)
> > >
> > > The function designator `free' auto-decays into a function pointer,
> > > which is compared to a null pointer constant: 0. The ! operator does
> > > that same thing implicitly, but is fully equivalent to it.
> > ---
> > Free autodecays to a function pointer?
>
> In the use case at hand: yes, it does.
>
> > In what language?
>
> Standard C.
Wasn't that supposed to go to the newlib list where this has been
discussed originally?
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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