From:	"Michael Farnham" <MCFARNHAM AT prodigy DOT net>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Lack of overflow problem
Date:	Fri, 7 Jan 2000 04:38:34 -0600
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Chris Underwood <underwoodc AT logica DOT nospam DOT com> wrote in message
news:854cnj$453 AT romeo DOT logica DOT co DOT uk...
>
> >Rob McCrea (r_mccrea AT hotmail DOT com) wrote:
> >: My expression won't recognize the overflow...
> >:
> >: while ((s+1) > s) s++;
> >:
> >: is an infinite loop.  What's up with that?
> >: Apparently the condition is being evaluted as (1>0).
> >: That's not right is it?  I'm compiling with gpp -Wall testsize.cpp -o
> >: testsize.exe.
> >:
> >: Please, can someone explain why its not acting like a computer?
>
>
> I'm not sure exactly what you're claiming is wrong here, but you might
not
> realise that sooner or later, given that 's' is likely an integer of some
> size or another, it'll wrap around, and your loop will exit. For example,
if
> 's' is an unsigned char you will loop until s = 255, then s+1 will be 256
> which overflows and wraps round to 0. (0 > 255) is false, and you'll exit
> the loop.
>
> Chris
>
>

I think that is what was expected.

It is possible that the compiler has optimized this loop to while(true)
s++;.
In the real world s + 1 > s is always true. Sometimes compilers make
optimizations that a human being would not make.

I have not tested the code and therefore do not know that this is
happening.
But it is an explanation that fits the observed facts.


Regards
Mike

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