From: pausch AT saafNOSPAM DOT se (Paul Schlyter)
Newsgroups: comp.os.msdos.djgpp,comp.os.msdos.programmer
Subject: Re: Detecting Windows and Windows directory from DOS
Date: 21 Mar 2000 23:47:58 +0100
Organization: Svensk Amat|rAstronomisk F|rening (SAAF)
Lines: 38
Message-ID: <8b8u6u$fv5$1@merope.saaf.se>
References: <8am5ub$o0v$1 AT news6 DOT svr DOT pol DOT co DOT uk> <38D6844B DOT 876E5631 AT bigfoot DOT com> <MPG DOT 134160c4f0a1f29b98ae44 AT news DOT mindspring DOT com> <38D7E5F5 DOT ED6FB969 AT bigfoot DOT com>
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

In article <38D7E5F5 DOT ED6FB969 AT bigfoot DOT com>,
Richard Dawe  <richdawe AT bigfoot DOT com> wrote:
 
> By the way, I think you mean "in user code they _may_ lead to undefined
> behavior" rather than "in user code they lead to undefined behavior",
> which is a bit harsh. ;)
 
"Undefined behaviour" doesn't imply programs crashing or otherwise
malfunctioning.  "Undefined behavior" is merely undefined: on some
platforms it may work just fine, on others there may be silent
errors, and on still others there may be a spectacular crash.  It may
even be so that on all current platforms the program works fine, but
there is a potential for malfunction on future platforms.
 
If one #define's a symbol which belongs to the system namespace
rather than the user namespace, one runs the risk of a name collision.
This name collision may cause a compile-time error (e.g. if some
system header already has #define'd the same symbol), or some silent
error (if some other system header behaves differently if this
symbol is #define'd).  There's no guarantee of there being an error,
but there is a possibility.
 
"Defined behaviour" on the other hand means a guarantee that the
program should behave in a specific way, on all standard-conforming
platforms.  "Undefined behaviour" is merely the absence of this
guarantee -- but it doesn't mean there'll be an error on every
standard-conforming platform.
 
Therefore it is quite appropriate to say in this case that it leads
to undefined behaviour: the program may work, but there's no guarantee
that it works.
 
-- 
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Paul Schlyter,  Swedish Amateur Astronomer's Society (SAAF)
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