21 Sep
2020
21 Sep
'20
8:24 a.m.
ISO requires that NULL be defined in locale.h, stddef.h, stdio.h, stdlib.h,
string.h, time.h, wchar.h, and their C++ equivalents clocale etc.. It's
pretty unlikely that you can write any useful code at all without NULL
being defined as a side effect.
On Sun, Sep 20, 2020 at 8:01 PM Clem Cole <clemc(a)ccc.com> wrote:
I was also stating (under Henry’s 10th) using a
properly defined macro
with the complete cast scheme will be correct and portable to all known
conforming C compilers no matter the target HW architecture — which in a
commercial SW setting is highly valued.
Clem
On Sun, Sep 20, 2020 at 7:53 PM Clem Cole <clemc(a)ccc.com> wrote:
Norman NULL has to be defined and I said
that/showed it. The standard
says where. I was not trying to compile NULL without a definition which I
agree it not legal. If that is what Doug was implying I missed understood
him but I note NULL was introduced in Typesetter C /V7 where those compiler
s set it to 0 in studio but the ANSI/ISO moved it.
On Sun, Sep 20, 2020 at 7:03 PM Norman Wilson <norman(a)oclsc.org> wrote:
Sent from a handheld expect more typos than usual
Doug McIlroy:
To put it more strongly. this is not a legal C source file.
char *s = NULL;
But this is.
char *s = 0;
Clem Cole:
67)The macro NULL is defined in <stddef.h> (and other headers) as a
null
pointer constant; see 7.19.
====
$ cat null.c
char *s = NULL;
$ cat zero.c
char *s = 0;
$
zero.c is a legal C program. null.c is not. Create
files exactly as shown and compile them if you don't
believe me.
Prepend `#include <stddef.h>' (or <stdlib.h> or <stdio.h>)
to null.c and it becomes legal, but I think that's Doug's
point: you need an include file.
Personally I prefer to use NULL instead of 0 when spelling
out a null pointer, because I think it's clearer:
if ((buf = malloc(SIZE)) == NULL)
error("dammit andrew");
though I am willing to omit it when there's no confusion
about = vs ==:
if (*p)
dammit(*p, "andrew");
But that's just a question of style, and Doug's is fine too.
The language does not require the compiler to pre-define
NULL or to recognize it as a keyword; you have to include
an appropriate standard header file.
Norman Wilson
Toronto ON (not 0N nor NULLN)
--
Sent from a handheld expect more typos than usual
--