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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: "Catch-23: The New C Standard,Sets the World on Fire" by Terence Kelly with Special Guest Borer Yekai Pan
Date: Sun, 09 Apr 2023 12:55:24 -0700
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Ben Bacarisse <ben.usenet@bsb.me.uk> writes:

> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>
>> Kaz Kylheku <864-117-4973@kylheku.com> writes:
>>
>> [miscellaneous suggestions taken out]
>>
>>> On 2023-04-06, John Forkosh <forkosh@panix.com> wrote:
>>>
>>>>   void *realloc0 ( void *ptr, size_t size ) {
>>>>     void *reptr = NULL;
>>>>     if ( size < 1 ) {
>>>>       if ( ptr != NULL ) free(ptr); }
>>>>     else reptr = realloc(ptr,size);
>>>>     return ( reptr ); }
>>>
>>> Consider:
>>>
>>>   return (size == 0) ? free(ptr), NULL : realloc(ptr, size);
>>>
>>> which avoids multiple returns, variable assignment, and
>>> verbiage.
>>
>> I agree with the general tone of this suggestion.  Unfortunately
>> however the particular code suggested might not compile (because
>> the macro NULL might be #define'd to be 0, which can result in an
>> error).
>
> I'm not sure what you mean.  "Can result in an error" sounds a bit
> vague.  I know from
>
>> ... the main point about
>> avoiding the potential compilation error ...
>
> that you mean a compilation error, but that's not a standard term.

If NULL is #define'd to be 0, then a diagnostic is required.  The
problem can be seen by attempting to compile this version:

    void *
    realloc0( void *p, size_t size ){
        return  size == 0  ? free( p ), 0  : realloc( p, size );
    }

The presence of a required diagnostic means the compilation can
fail, without needing any other cause.  Of course that doesn't
mean a compilation must fail, but it can fail, and will fail
if for example -Werror was used.  Does that clarify what I was
trying to get at?