Path: utzoo!attcan!utgpu!watmath!iuvax!uxc.cso.uiuc.edu!tank!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: "do ... while ((NULL + 1) - 1);" -- valid C?
Message-ID: <19108@mimsy.UUCP>
Date: 16 Aug 89 12:57:19 GMT
References: <1043@levels.sait.edu.au> <828@ruso.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 16

In article <828@ruso.UUCP> wolfgang@ruso.UUCP (Wolfgang Deifel) writes:
>I think it's a difference if you write " NULL + 1 " ( which is non-
>portable C, NULL is a machine dependent macro ) and " strchr(...) + 1 ".

There is a difference.  However:

>strchr() is a function that returns always a legal value. If strchr fails
>it will return (char*)0 ( regardless of the machine or the compiler ),
>and here it's legal to add '1' ( the result is (char*)1 ).

this is what we just got finished saying is false: it is NOT legal to
add 1 to (char *)0; indeed, it is not legal to add 1 to any of the
various infinite varieties of nil pointer.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris