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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: question about nullptr
Date: Mon, 12 Aug 2024 18:10:44 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>
>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>
>>> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>>> [...]
>>>
>>>> This posting has inspired me to try using (long)0.0
>>>> whenever a null pointer constant is needed.  As for
>>>> example
>>>>
>>>>     (void*){ (long)0.0 }
>>>>
>>>> as an argument to a variadic function where a pointer
>>>> is expected.
>>>
>>> But surely ((void*)('/'/'/'-'/'/'/')) is more elegant.
>>
>> Surely not.  Furthermore the form I showed has a point,
>> whereas this example is roughly the equivalent of a
>> first grade knock-knock joke.
>
> I was of course joking.  I assumed you were as well.
>
> What is the point of (void*){ (long)0.0 }?  I don't believe it's a
> null pointer constant even in C23.

The null pointer constant is (long)0.0, which it must be for the
compound literal to work.  Besides making it obvious that (long)0.0
is a null pointer constant, the compound literal is safer than
using just a cast.

> My example is.

Your example actually has two null pointer constants:  the
expression being casted, and the full expression casting a null
pointer constant to (void*).  But in neither case is that especially
obvious.  Also the expression you wrote is less safe.  For example,
if it had been written ((void*)('/'/'/'+'/'/'/')), the result would
still be legal C, and compile without problem, but would very likely
not be what was desired.  By contrast, if the compound literal had
been written (void*){ (long)1.0 }, it simply would not give a clean
compile, indicating that something is likely askew.