Subject: Re: sys/null.h
To: Roland Illig <>
From: Greg A. Woods <>
List: tech-userlevel
Date: 04/15/2005 15:51:46
[ On Wednesday, April 13, 2005 at 18:09:32 (+0200), Roland Illig wrote: ]
> Subject: sys/null.h
> * What happens on I32LP64 systems?
>    fprintf(stderr, "%#p %#p\n", NULL, NULL, 1, 2, 3, 4);
>    I would expect the answer to not be "0x0 0x0".

You forgot the _necessary_ parameter casts.

Just because you're using C with prototypes doesn't mean you can get
away without casting some parameters to varargs/stdargs functions.

In fact when you use "%p" you really should always cast the relevant
parameter using "(void *)", even if it is already some other type of
pointer because "%p" is only defined for pointers to "void" objects.

Besides, portable code _MUST_ acknowledge that NULL may be defined as
the plain integer value zero.

> * Why don't we always #define NULL ((void *) 0) ?

Sane use of NULL in C does not require it to be anything but a plain
integer zero, and indeed anything else can cause far more headaches and
confusion than is necessary since NULL gets used in real code in many
places where a pointer type is not desired.  (Maybe it shouldn't be, but
that's the way it is; and the standard doesn't really preclude the use
of the NULL macro in many of the places were a pointer type is not
desired either.)

>    (We don't have to be pre-ANSI compatible anyway.)

Yes, NetBSD _MUST_ be able to compile both pre-ANSI code and code that
uses NULL as an int or char value thus the public headers really must
use a plain integer zero for NULL.

						Greg A. Woods

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