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From: bc@halley.UUCP (Bill Crews)
Newsgroups: comp.lang.c,comp.unix.wizards
Subject: Re: pointer alignment when int != char *
Message-ID: <286@halley.UUCP>
Date: Tue, 1-Sep-87 19:09:38 EDT
Article-I.D.: halley.286
Posted: Tue Sep  1 19:09:38 1987
Date-Received: Sat, 5-Sep-87 17:20:49 EDT
References: <493@its63b.ed.ac.uk> <6061@brl-smoke.ARPA> <3812@spool.WISC.EDU> <2130@umn-cs.UUCP> <6357@brl-smoke.ARPA>
Reply-To: bc@halley.UUCP (Bill Crews)
Organization: Tandem Computers, Austin, TX
Lines: 24
Xref: mnetor comp.lang.c:4154 comp.unix.wizards:4077

In article <6357@brl-smoke.ARPA> gwyn@brl-smoke.ARPA (Doug Gwyn ) writes:
>In article <2130@umn-cs.UUCP>, randy@umn-cs.UUCP (Randy Orrison) writes:
>> In article <483@mtxinu.UUCP> ed@mtxinu.UUCP (Ed Gould) writes:
>> >Pointers may be subtracted *only* if they point to members of the same
>> >array of elements.
>> How is this determined?  example:
>> strlen(s)
>> 	return (c-s);
>
>Obviously all characters in a string are in the same object (be it
>(char []) or chunk of malloc()-allocated storage.

It seems to me that everyone is ignoring his Ed's point.  Let's say a function
is to take two pointer arguments, a pointer to a string and a pointer
into the string.  What you say seems to indicate that arithmetic expressions
involving both pointers, such as their difference, will produce unpredictable
results at execution time, because the called function has no way of knowing
whether the pointers are actually to the same "string" or not.

-bc
-- 
Bill Crews                                   Tandem Computers
                                             Austin, Texas
..!seismo!ut-sally!im4u!esc-bb!halley!bc     (512) 244-8350