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From: ed@mtxinu.UUCP (Ed Gould)
Newsgroups: comp.lang.c,comp.unix.wizards
Subject: Re: pointer alignment when int != char *
Message-ID: <483@mtxinu.UUCP>
Date: Thu, 27-Aug-87 19:04:23 EDT
Article-I.D.: mtxinu.483
Posted: Thu Aug 27 19:04:23 1987
Date-Received: Sat, 29-Aug-87 13:24:43 EDT
References: <493@its63b.ed.ac.uk> <6061@brl-smoke.ARPA>
Reply-To: ed@mtxinu.UUCP (Ed Gould)
Organization: mt Xinu, Berkeley
Lines: 19
Xref: mnetor comp.lang.c:3975 comp.unix.wizards:3933

># To subtract two independent large-model pointers of the type
># segment:offset, I tried this:
># 
>#      (unsigned long) p2 - (unsigned long) p1
># 
>
>This is bad practice.

It's also not legal in the proposed ANSI C standard.  Pointers
may be subtracted *only* if they point to members of the same
array of elements.  Casting them has no real effect on a byte-
addressed machine; it's not at all obvious what it should do
on other machines.

-- 
Ed Gould                    mt Xinu, 2560 Ninth St., Berkeley, CA  94710  USA
{ucbvax,decvax}!mtxinu!ed   +1 415 644 0146

"A man of quality is not threatened by a woman of equality."