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 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 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 wrote: >> >>> 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 (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 ' (or or ) >>> >>> 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 >> >> >> -- > Sent from a handheld expect more typos than usual >