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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Casting the return value of ...
Date: Thu, 28 Mar 2024 15:37:22 -0700
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Kaz Kylheku <433-929-6894@kylheku.com> writes:
> On 2024-03-28, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
>> The warnings I get from gcc are:
>>
>> warning: ISO C forbids conversion of function pointer to object pointer type [-Wpedantic]
>> warning: ISO C forbids conversion of object pointer to function pointer type [-Wpedantic]
>>
>> With -pedantic-errors, these become fatal errors.
>>
>> I disagree with gcc.  ISO C doesn't define the behavior, but it doesn't
>> forbid the conversion.
>
> It's never good for a diagnostic to be stating a blatant falsehood,
> regardless of whether the presence of the diagnostic is a good idea
> or not.
[...]
> I'm actually opening a GCC bugzilla about this right now.

I should have remembered that I reported this as a bug in 2017:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83584

That bug report was closed (inappropriately IMHO) as a duplicate of

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=11234

A commenter on bug #83584 cites the C99 Rationale:
"Even with an explicit cast, it is invalid to convert a function pointer
to an object pointer or a pointer to void, or vice versa."

It's not clear what "invalid" means in that context, and in any case the
Rationale is not normative.

N1570 Annex J 5.7 mentions casting between object pointers and function
pointers as a common extension.

Kaz, I see you've submitted
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114526
which has (inappropriately IMHO) been closed as a duplicate of #11234.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Medtronic
void Void(void) { Void(); } /* The recursive call of the void */