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From: hamish@unisoft.UUCP (Hamish Reid)
Newsgroups: comp.lang.c
Subject: Re: When is a cast not a cast?
Message-ID: <2052@unisoft.UUCP>
Date: 18 May 89 19:34:00 GMT
References: <2747@buengc.BU.EDU> <10191@smoke.BRL.MIL> <406@skye.ed.ac.uk> <10276@smoke.BRL.MIL> <2890@buengc.BU.EDU>
Reply-To: hamish@unisoft.UUCP (Hamish Reid)
Lines: 60

I can't stand it any longer...

In article <2890@buengc.BU.EDU> bph@buengc.bu.edu (Blair P. Houghton) writes:
>
>>What properties does t hypothetically have?
>
>It has the property that you can now subtract
>
>    char *pnew, *r;
>    pnew = t - r
>
>and expect pnew to point to the location referred to p that is
>the same offset as q is referred to r.
 
Let's try this just one more time (but see also my other posting
answering Blair's more general points):

Blair	- what is the type of the result of subtracting one pointer
	from another?

	[Hint: it's not an address unless you cast it that way - and
	then it wouldn't in general be a meaningful address]

	- what is the *difference* between two pointers (a la
	subtraction)?

	[Hint: it's not an address unless you cast it that way - and
	then it wouldn't be a meaningful address]

	- what is the type of "t" above?

	[Hint: As the original poster (Tobin?) pointed out, it's not a
	char *, nor is it really well-defined).]

>>[Doug Gwynn:] Other postings have explained why we don't think a reasonable,
>>consistent model for this feature is possible.
>
>"Why we don't think...possible"??  Not only is it possible, it's sensible.
>As to whether we think it is so, that is irrelevant.

You might want to ponder who the "we" is above. Doug Gwynn and the rest
of the Ansi C standards commitee? Concerned Citizens for C Programming
Semantics (:-))?  We poor folks in the C semantics and/or
compiler-writing community?  But gee, Blair Houghton (the original Man
With The Pointer Scaling Problem) says it's possible, it's sensible, so
it *must* be so. QED. RIP. Etc.

>We don't think
>fusion is possible, either, unless we consider that it's going on all
>over the place (well, not _all_ over the place, but in all those jillions
>of stars...!)

Speak for yourself. That was the Royal "we", I presume? There's little
else that would account for the imperiously ignorant tone of your
posting...

	Hamish
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Hamish Reid             UniSoft Corp, 6121 Hollis St, Emeryville CA 94608 USA
+1-415-420-6400         hamish@unisoft.com,         ...!uunet!unisoft!hamish