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From: mouse@mcgill-vision.UUCP (der Mouse)
Newsgroups: comp.lang.c
Subject: Re: How big is a (??? *)
Message-ID: <790@mcgill-vision.UUCP>
Date: Tue, 2-Jun-87 21:46:42 EDT
Article-I.D.: mcgill-v.790
Posted: Tue Jun  2 21:46:42 1987
Date-Received: Thu, 11-Jun-87 03:00:54 EDT
References: <737@edge.UUCP>
Organization: McGill University, Montreal
Lines: 31

In article <737@edge.UUCP>, doug@edge.UUCP (Doug Pardee) writes:
> Well, I would have thought that we'd have beaten this
> (char *)!=(int *) thing to death.

I rather think we have....

> I want to do what is sometimes called "object-oriented" programming.

> [wants to return "handles" to internal structures]

> Possibility #1:  We cavalierly declare that no pointers are longer
> than char pointers:
>      sizeof (char *)   >=   sizeof (anything *)
> and create object handles by casting the pointers with (char *).

This should work, but not because of the reason you quoted.  K&R says,
and presumably ANSI follows them in saying, that a pointer to any
object can be cast to a pointer to any smaller object and back without
change.  Since a char is the smallest object available, any pointer can
be cast to (char *) and back without change.  Therefore, this scheme is
safe, regardless of the sizes of the pointers.  (Since more of a
smaller object can fit into memory, this would tend to imply the
inequality you quoted, but it does not require it.)

If ANSI does not support this argument, I would certainly hope they
have some analogous pointer type, which can be substituted for (char *)
to repair the above exposition.

					der Mouse

				(mouse@mcgill-vision.uucp)