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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c++,comp.lang.c
Subject: Re: =?utf-8?Q?=E2=80=9CChattyG?= takes a college freshman C/C++ programming =?utf-8?Q?exam=E2=80=9D?=
Date: Fri, 13 Oct 2023 10:04:31 -0700
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MarioCCCP <NoliMihiFrangereMentulam@libero.it> writes:
> On 08/10/23 21:31, Chris M. Thomasson wrote:
>> On 10/8/2023 4:22 AM, candycanearter07 wrote:
>>> On 10/8/23 04:55, Anton Shepelev wrote:
>>>> I disagree.  A function returns the value of its declared
>>>> return type.  And although C allows the definition of self-
>>>> referential structs, it does allow the declaration of self-
>>>> referencial functions.
>>>
>>> What if you typedef'd the function pointer?
>>>
>>> Also, you could probably get away with it by just setting it to a
>>> void pointer and casting the return value to the function pointer.
>> Not sure if that's allowed. A function pointer cast to a 
>> void pointer, which in turn is cast back to a function pointer is
>> undefined? What am I forgetting here?
>
> mine is not an answer but a doubt : maybe void * and void (*) (void)
> could require different alignment restrictions ?
>
> I dunno whether or not void * has any restriction at all ...

It does.

Object pointers can be converted to void* and back without loss of
information.  Quoting the C standard:

    A pointer to void may be converted to or from a pointer to any
    object type. A pointer to any object type may be converted to a
    pointer to void and back again; the result shall compare equal to
    the original pointer.

Function pointers can be converted to other function pointer types and
back again without loss of information.  Quoting the C standard again:

    A pointer to a function of one type may be converted to a pointer to
    a function of another type and back again; the result shall compare
    equal to the original pointer. If a converted pointer is used to
    call a function whose type is not compatible with the referenced
    type, the behavior is undefined.

But conversions between object pointer types (including void*) and
function pointer types have undefined behavior.

Many implementations do support meaningful conversion between function
pointer types and void* (and POSIX requires such conversions to work at
least for values returned by dlsym()).  On most implementations, all
pointers have the same representation, but that's not required.  A
conforming implementation could, for example, have 64-bit object
pointers and 128-bit function pointers.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */