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From: franka@mmintl.UUCP (Frank Adams)
Newsgroups: comp.lang.c
Subject: Re: char (*a)[]  (was: Style [++i vs i++])
Message-ID: <2310@mmintl.UUCP>
Date: Fri, 14-Aug-87 20:27:22 EDT
Article-I.D.: mmintl.2310
Posted: Fri Aug 14 20:27:22 1987
Date-Received: Thu, 20-Aug-87 04:50:13 EDT
References: <8298@brl-adm.ARPA> <587@cblpe.ATT.COM> <189@xyzzy.UUCP> <1987Aug10.192923.7879@sq.uucp>
Reply-To: franka@mmintl.UUCP (Frank Adams)
Organization: Multimate International, E. Hartford, CT.
Lines: 21

In article <1987Aug10.192923.7879@sq.uucp> msb@sq.UUCP (Mark Brader) writes:
>Wayne Throop writes:
>>... but *also* because it performs arithmetic on a null pointer, and
>>of course, this is illegal.)
>
>Um, I don't think so, Wayne; it's just that the result, if you indirect
>through such a pointer, is undefined.

Operations which produce undefined results are a special case of illegal
operations.  Specifically, they are illegal operations where the response of
the program can be anything.  Including, at the extremes, aborting with an
error message, or performing in some well-defined way as an implementation
extension.

On the other hand, I don't know of any programs (ala lint) which perform
flow analysis on C programs, and nothing less will detect this kind of bug.
Lint certainly cannot be expected to find it.
-- 

Frank Adams                           ihnp4!philabs!pwa-b!mmintl!franka
Ashton-Tate          52 Oakland Ave North         E. Hartford, CT 06108