Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!nrl-cmf!cmcl2!brl-adm!brl-smoke!gwyn
From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: comp.lang.c
Subject: Re: C machine
Message-ID: <7199@brl-smoke.ARPA>
Date: 29 Jan 88 20:01:57 GMT
References: <461@auvax.UUCP> <28700025@ccvaxa> <7159@brl-smoke.ARPA> <8728@ism780c.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 15

In article <8728@ism780c.UUCP> marv@ism780.UUCP (Marvin Rubenstein) writes:
-The problem with a header file defining a type ptrdiff_t is that the the
-defined type must be one of the types in the base C language.  If an
-implementation defines ptrdiff_t such that sizeof(ptrdiff_t) == sizeof(void*)
-then p1-p2 may overflow.

"As with any other arithmetic overflow, if the result does not fit in the
space provided, the behavior is undefined."

It is up to the implementation to choose a reasonable size for ptrdiff_t.

-BTW, the definition of pointer difference in K&R is "if p and q point to
-members of the same array , p-q is the number of elements between p and q."
-One way to interpret this is the following:

Yes, that's been fixed in the proposed ANSI C standard.