Newsgroups: comp.lang.c
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Efficient coding considered harmful?
Message-ID: <1988Oct31.175926.13316@utzoo.uucp>
Organization: U of Toronto Zoology
References: <3105@hubcap.UUCP> <34112@XAIT.XEROX.COM> <1700@dataio.Data-IO.COM> <8775@smoke.BRL.MIL> <7421@ihlpl.ATT.COM>
Date: Mon, 31 Oct 88 17:59:26 GMT

In article <7421@ihlpl.ATT.COM> knudsen@ihlpl.ATT.COM (Knudsen) writes:
>> 	for (p = &a[j]; --p >= a; )
>> which is nonportable.)
>
>Why not portable? ...

It terminates by running p off the beginning of a, and comparing it to
a to detect this situation.  The result of running a pointer off the
beginning of an array is (and always has been) undefined.  On some
segmented machines, this can and does cause trouble.
-- 
The dream *IS* alive...         |    Henry Spencer at U of Toronto Zoology
but not at NASA.                |uunet!attcan!utzoo!henry henry@zoo.toronto.edu