Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!att!ihlpb!TSfR!usenet
From: usenet@TSfR.UUCP (usenet)
Newsgroups: comp.lang.c
Subject: Re: When is a cast not a cast?
Summary: Whoa..
Message-ID: <546@TSfR.UUCP>
Date: 18 May 89 05:52:39 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: orc@TSfR.UUCP (David L. Parsons)
Followup-To: comp.lang.c
Organization: This Space for Rent - Lisle, IL
Lines: 45
Expires:

In article <2890@buengc.BU.EDU> bph@buengc.bu.edu (Blair P. Houghton) writes:
[more discussion of the properties of pointer+pointer]
>
>>What is its type hypothetically supposed to be?
>
>char *
>
>>What can one legally do with it?
>
>What one can legally do between (consenting) integers?

  Eeek.  Hopefully not.  If it's integerish, it associates & commutes,
  and if it's a pointer, well....

    pointer-pointer yields an int

  replace a pointer with a pointer+pointer....

    (pointer+pointer)-pointer yields an int

  then rearrange the parenthesis....

    pointer+(pointer-pointer) yields an int

  you'd get (using pointer-pointer yields an int) ...

    pointer+int yields an int

  which conflicts with...

    pointer+int yields a pointer

> ... Not only is it possible, it's sensible.

  Not really, not with the abilities you give it above.

  What does pointer+pointer give you, aside from clever loop optimizations?
  Wouldn't the task of loop optimizing be better served by making a type
  that holds pointer+pointer values and that can have a pointer subtracted
  from it to yield another pointer, but doesn't allow any other operation?



   -david parsons
   -orc@pell.uucp