Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: James Kuyper <jameskuyper@alumni.caltech.edu>
Newsgroups: comp.lang.c
Subject: Re: question about nullptr
Date: Wed, 10 Jul 2024 18:50:00 -0400
Organization: A noiseless patient Spider
Lines: 45
Message-ID: <v6n36o$239h6$2@dont-email.me>
References: <v6bavg$3pu5i$1@dont-email.me> <20240706054641.175@kylheku.com>
 <v6bfi1$3qn4u$1@dont-email.me> <l9ciO.7$cr5e.2@fx05.iad>
 <877cdyuq0f.fsf@bsb.me.uk> <2ckiO.19403$7Ej.4487@fx46.iad>
 <87plrpt4du.fsf@bsb.me.uk> <9bCiO.7108$sXW9.3805@fx41.iad>
 <877cdwu9s1.fsf@nosuchdomain.example.com> <20240708222804.00001654@yahoo.com>
 <86le2b9ru6.fsf@linuxsc.com> <8734ojxlg7.fsf@nosuchdomain.example.com>
 <86msmp8fld.fsf@linuxsc.com> <87cynluekl.fsf@nosuchdomain.example.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Injection-Date: Thu, 11 Jul 2024 00:50:00 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="7338e67614b36e18c17f3563b3f8bed2";
	logging-data="2205222"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+Xel40667IWMlCEmAVQoQX8XVOPRH2S2U="
User-Agent: Mozilla Thunderbird
Cancel-Lock: sha1:LGGo7OzRBZvebWRXqV0fvSe5+LY=
Content-Language: en-US
In-Reply-To: <87cynluekl.fsf@nosuchdomain.example.com>
Bytes: 2828

On 7/10/24 17:23, Keith Thompson wrote:
> 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.

I think you're right about that.

"An integer constant expression132) ... shall only have operands that
are ... compound literal constants of arithmetic type that are the
immediate operands of casts. ... Cast operators in an integer constant
expression shall only convert arithmetic types to integer types, ...",
so (long)0.0 is permitted."

While (void*) looks like a cast, in this context it is a compound
literal of pointer type, which is not allowed. If he had written

(void*)(long)0.0

that would not have been a problem.