Re: Out-of-bounds pointers

Article View: comp.std.c

Article #660

#660

From: Larry Jones
Date: Tue, 03 Oct 1989 22:01

21 lines
1321 bytes

In article <1009@mtxinu.UUCP>, ed@mtxinu.COM (Ed Gould) writes:
> Is the following code conformant?  It's clear that it's not legal to
> dereference the pointer in its "illegal" state, but is the p++ line
> guaranteed to return it to a valid value?  What would it (be expected
> to) print?
> 
> 		p = buf;
> 		p--;	/* p contains an illegal value: &buf[-1] */
> 		p++;	/* hopefully, now p == &buf[0] */

Nope.  Once you've decremented p you've entered the twilight zone
of undefined behaviour where your program could dump core, play
the Star Spangled Banner, or continue on.  If it continued, the
increment may or may not set it pointing to buf again.
----
Larry Jones                         UUCP: uunet!sdrc!scjones
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"I have plenty of good sense.  I just choose to ignore it."
-Calvin

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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!sdrc!scjones
From: scjones@sdrc.UUCP (Larry Jones)
Newsgroups: comp.std.c
Subject: Re: Out-of-bounds pointers
Message-ID: <844@sdrc.UUCP>
Date: 3 Oct 89 22:01:24 GMT
References: <1009@mtxinu.UUCP>
Organization: Structural Dynamics Research Corp., Cincinnati
Lines: 21

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