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From: ergo@netcom.UUCP (Isaac Rabinovitch)
Newsgroups: comp.lang.c
Subject: Re: What C compilers have non-zero null pointers?
Message-ID: <12288@netcom.UUCP>
Date: 17 Jul 90 19:38:10 GMT
References: <GMKM5FY@drivax.UUCP> <9007161750.AA00664@edison.CHO.GE.COM>
Organization: UESPA
Lines: 35

In <9007161750.AA00664@edison.CHO.GE.COM> rja@edison.cho.ge.com (rja) writes:

>I used to use a compiler for MSDOS and the 80x86 cpus 
>whose NULL pointer was F000:0000 hex when examined via
>a debugger.  It of course did compile fine as long as one
>used sense and compared pointers to NULL rather than 
>a constant of zero...

True.  But what the "NULL should always be 0" diehards want is not to
write (for example)

	for (ptr = fist; ptr != 0; ptr = ptr->next)

in which 0 should probably be #DEFINED anyway, but rather

	for (ptr = first; ptr ; ptr = ptr->next)

which produces tighter code and (most important of all) looks
spiffier.  It has the elegance of expression old C hands crave.

>Compilers where NULL isn't represented as all zero bits
>just aren't that uncommon.

My '78 K&R says that assigning 0 to a pointer is (or was) guarranteed
to produce a NULL, even on compilers that didn't like other
integer-to-pointer assignments.  But, interestingly, they did *not*
guarantee, even then, the reverse!
-- 

ergo@netcom.uucp			Isaac Rabinovitch
atina!pyramid!apple!netcom!ergo		Silicon Valley, CA
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	"I hate quotations.  Tell me what you know!"
			-- Ralph Waldo Emerson