Re: Divide by 0 - exception thrown?

From:

David Wilkinson <no-reply@effisols.com>

Newsgroups:

microsoft.public.vc.language

Date:

Fri, 13 Oct 2006 13:12:37 -0400

Message-ID:

<ecZUEru7GHA.3604@TK2MSFTNGP02.phx.gbl>

Jason Doucette wrote:

David, thanks for your story. It's great to hear about real world
experiences like this.

A few questions:

1. You said, "the moral was: always check for divide by zero rather than
relying on the standard behavior." But, how do you check for divide by
zero, when checking denominator != 0.0 is not sufficient to prevent an
overflow? In reality, you wish to prevent an overflow, not merely prevent a
divide by 0.

2. It appears your story implies an astonishing fact: That the FP status is
not maintained per thread / process. Is this really true? That means even
if I modified the FP exception masking, then I could start crashing other
software on the machine that expects the default status. In fact, two
pieces of software could be fighting back and forth attempting to set the
exception masking as they see fit. Thus, it would seem that the proper
behaviour of any application is to: A. not change the FP exception masking,
and B. not assume the FP exception masking is set to default.

3. On the CodeGuru forums (
http://www.codeguru.com/forum/showthread.php?p=1472920 ) it was stated that
"By default, floating point exceptions are turned on. ... and the VC++
standard library happens to turn them off." Thus, this would indicate that
whenever a program that is compiled with VC++ is run, it changes the default
behaviour until another application changes it back. Can this possibly be
true?

Thanks again for your story and advice,

Jason:

1. In my case the divide by zero was really a divide by zero and
represented a logic flaw in my algorithm. Have to confess that I just
put in a test for zero divide.

2. Could be this only happened when I printed from my own application; I
don't remember.

David Wilkinson