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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: function pointer question
Date: Wed, 07 Jan 2026 05:59:39 -0800
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scott@slp53.sl.home (Scott Lurndal) writes:

> highcrew <high.crew3868@fastmail.com> writes:
>
>> On 1/6/26 3:50 PM, Waldek Hebisch wrote:
>>
>>> Well, '(void)*foo' effectively says "foo" is not a null pointer
>>> (otherwise if would be undefined behaviour).  Good optimizer
>>> will_not_ dereference foo, but keep information for further
>>> use.
>>
>> Hehe, now that I understand more of UB, that is correct, but
>> I don't think you can *rely* on the optimizer behavior, can you?
>
> Say you have a function xxx defined in a header file, but that
> function is only used in certain source files that include that
> header file.
>
>   int
>   xxx(const char *a, size_t b)
>   {
>       /* do something with a and b */
>   }
>
> When compiling with -Wall, a translation unit that doesn't
> reference 'xxx' yet requires other components of the
> header file will get a warning (error with -Werror) that
> the function was unreferenced.   It is not uncommon to
> make a void reference to the function in those translation
> units to avoid the warning, e.g.
>
> yyy.c:
>
> #include "xxx.h"
>
> int
> yyy(...)
> {
>    <function body>
>    (void)xxx;
> }

It seems better to address this problem in the header file
itself.  It's easy to do that by adding a second function
in the header file and having them mutually reference
each other.

> xxx in this context devolves to a function pointer, IIUC.

Just use (void)&xxx.  Now you're sure.