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From: wmam@sphinx.UChicago.UUCP (tony mason)
Newsgroups: net.unix-wizards
Subject: Re: Microport Unix -- Large Model Problems
Message-ID: <775@sphinx.UChicago.UUCP>
Date: Wed, 5-Nov-86 21:49:53 EST
Article-I.D.: sphinx.775
Posted: Wed Nov  5 21:49:53 1986
Date-Received: Fri, 7-Nov-86 22:41:58 EST
References: <188@vsedev.VSE.COM> <401@maynard.UUCP> <245@rabbit1.UUCP> <347@prairie.UUCP> <405@maynard.UUCP>
Reply-To: wmam@sphinx.UUCP (tony mason)
Distribution: net
Organization: Univ. of Chicago Computation Center
Lines: 38
Keywords: Microport, Unix, Memory, Segmentation, lint

In article <405@maynard.UUCP> campbell@maynard.UUCP (Larry Campbell) writes:
>In article <347@prairie.UUCP> dan@prairie.UUCP (Daniel M. Frank) writes:
>>In article <245@rabbit1.UUCP> barber@rabbit1.UUCP (Steve Barber) writes:
>>>Another common problem is passing NULL as pointer argument.  NULL is
>>>#defined as 0, which is 2 bytes.  Large model pointers are 4 bytes, so
>>>the stack frame is now basically garbage.
>>
>>   This isn't really true.  Code in stdio.h for the SV/286 release
>>checks your memory model, and if it is large, defines NULL to be 0L,
>>which is the same size as a pointer.  It doesn't please lint, so the
>>best solution is still to cast it as appropriate (like (char *)0),
>>but you ARE generally safe, as long as you include stdio.h.
>
>I wonder why stdio.h doesn't just declare NULL as "(char *) 0", or,
>in the brave new world of ANSI X-whatever, "(void *) 0"?  This should
>do all the right things.

Note that in SCO XENIX (a/k/a MICROSOFT XENIX) they have declared NULL to be
of type (char *)0.  Of course, you always have someone who will abuse this by
doing something stupid such as:

	char	buf[10];

	buf[0] = NULL;

but they will learn!

The best practice is to cast it correctly (it sure makes lint happy!).


Tony Mason				> No opinions expressed here. Only cold hard
University of Chicago   > facts.

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