Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!unmvax!bbx!bbxsda!scott
From: scott@bbxsda.UUCP (Scott Amspoker)
Newsgroups: comp.std.c
Subject: Re: Out-of-bounds pointers
Message-ID: <202@bbxsda.UUCP>
Date: 5 Oct 89 17:20:24 GMT
References: <1009@mtxinu.UUCP> <4199@letni.UUCP>
Reply-To: scott@bbxsda.UUCP (Scott Amspoker)
Organization: Basis International,  Albuquerque, NM
Lines: 27


 In article <4199@letni.UUCP> doug@letni.LawNet.Com (Doug Davis) writes:
 >In article <1009@mtxinu.UUCP> ed@mtxinu.COM (Ed Gould) writes:
 >>     void
 >>     f() {
 >>            char bug[100];
 >             ^^^^^^^^^^  I assume you mean buf here, right?
 >>            char *p;
 >>
 >>            p = buf;
 >>
 >>            p--;	/* p contains an illegal value: &buf[-1] */
 >             ^^^ Opps,  You have now entered the land of illegal addresses,
 >                 normally called the twilight zone, incrementing the
 >                 pointer is no longer guarenteed to be == &buf[0], that
 >                 is installation dependent.  Most likely it will == something
 >                 really weird and you get a core dump.  Which one you get
 >                 is left as an exercise to the reader.

Agreed, it is undefined.  However *most likely* it will work just fine (based
on the several dozen systems I've worked with).  I would recommend avoiding
it though.

-- 
Scott Amspoker
Basis International, Albuquerque, NM
(505) 345-5232