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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: question about nullptr
Date: Sun, 07 Jul 2024 15:17:34 -0700
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scott@slp53.sl.home (Scott Lurndal) writes:
> Ben Bacarisse <ben@bsb.me.uk> writes:
[...]
>>Do you always cast NULL to a pointer in those (admittedly rare) cases
>>when one needs to?
>
> I may have back in the days when I was using Version 6 C and
> AT&T C where 
>
> $ grep NULL /work/reference/usl/uw2.01/usr/src/common/head/stddef.h
> #ifndef NULL
> #define NULL       0
>
>
> I use gcc today and it defines NULL for C as
>
> #define NULL ((void *)0)

Consider a variadic function that uses a null pointer to terminate the
argument list.  Then I always use NULL cast to the appropriate pointer
type.

For example, execl() requires a final argument that should be
`(char*)NULL`.

On the other hand, execl() is specified by POSIX, which also happens to
require NULL to be of type void* -- and you can pretty much get away
with using a void* null pointer where a char* null pointer is expected.

But casting NULL to the appropriate type (checked by reading the man
page) requires less thought.

I just about always use NULL, not 0, when I want a null pointer
constant.  Similarly, I use '\0', not 0, when I want a null character,
0.0 when I want a floating-point zero, and false when I want a Boolean
zero.  I just like being explicit.

In C23, I'll use nullptr rather than NULL *if* I don't care about
portability to pre-C23 compilers.  (I use nullptr in C++.)

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