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From: mouse@mcgill-vision.UUCP (der Mouse)
Newsgroups: comp.lang.c
Subject: Re: Silly program [was Re: Style [++i vs i++] ]
Message-ID: <875@mcgill-vision.UUCP>
Date: Sat, 29-Aug-87 23:52:17 EDT
Article-I.D.: mcgill-v.875
Posted: Sat Aug 29 23:52:17 1987
Date-Received: Sat, 12-Sep-87 15:48:11 EDT
References: <8298@brl-adm.ARPA> <587@cblpe.ATT.COM> <189@xyzzy.UUCP> <5272@utcsri.UUCP>
Organization: McGill University, Montreal
Lines: 33

In article <5272@utcsri.UUCP>, flaps@utcsri.UUCP (Alan J Rosenthal) writes:
> In article <513@ivax.doc.ic.ac.uk> dcw@doc.ic.ac.uk (Duncan C White) writes:
>> I think [someone - Duncan said "Alan" but Alan said "not me"] is
>> wrong here: if he really wants to add one byte, [well, one char] to
>> something that is a 'pointer to [int]' then I guess he should use:
>> 	p = (int *) ( 1 + (char *) p );

Yes.  But see below for comments on the wisdom of wanting to do such a
thing in the first place.

> ...except that when you dereference it you will get an address
> exception!

No, you *may* get an address exception.  On a VAX, for instance (and we
all know the whole world is a VAX, right? right? :-), this behaves
perfectly nicely.  Such unaligned pointers will probably be slightly
slower, but they work fine.

> Come on here, it is MEANINGLESS to do this kind of operation.

No, it is machine- and implementation-dependent, which is not the same
thing as meaningless.  Doing such a thing (moving an int pointer by
one char), except in seriously machine-dependent code, is probably
indicative of more serious problems.

> It's not just that "adding sizeof(int)" is what you probably want,
> it's that it's the only sensible thing to do.

No, the only sensible *portable* thing to do.

					der Mouse

				(mouse@mcgill-vision.uucp)