Use of NULL in UNIX & C (Was: Microport Unix -- Large Model Problems)

[Steve Barber]

I'm going to go out on a limb here, but it's a limb I'm comfortable on.

The use of the identifier NULL, as defined by stdio.h in all UNIXes I've
ever seen (v7, BSD4.[123], System III & V, Xenix, IN/ix, and many more
obscure variants), by itself as any kind of pointer, is a non-portable
usage and as such is incorrect for use in programs that are meant to be
used on more than one implementation of "UNIX" (loosely defined) or in
multiple memory models on those machines where this concept is relevant
(e.g. almost anything with an Intel processor).

When writing code, bite the bullet and type those extra 8 or so characters
when using NULL as a pointer value: (char *) NULL, (int *) NULL, or
whatever the type of the expression should be.  People, this will save
so much time in the long run and is the only general solution.  Tricks
with the preprocessor may work for some cases but not all, and I
guarantee that more time will be wasted on these than could be spent
typing in the casts to begin with.

When porting code of unknown or dubious ancestry to a new architecture,
one of the first things I do is to grep over the code for NULLs and fix
up those that are not cast properly since it is such a common error.
This check takes little time, and has a big payoff.  Bugs introduced by
these problems are almost always obscure.

In summary: If using NULL in an expression whose result is something
other than int, short, unsigned short, or unsigned int, always cast it.

I realize that some may disagree with this position.  Please do so
by mail, as I think I can probably convince you of my position
without a public flame war.  In fact, if anyone sees any flaws in the
above I'd love to hear about them.  I have directed followups to net.lang.c
as this is no longer really a UNIX issue.


-- 
Steve Barber    Rabbit Software Corp.
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