Re: This is undefined, but is it legal?

From:

Pete Becker <pete@versatilecoding.com>

Newsgroups:

comp.lang.c++

Date:

Sun, 27 Jul 2008 13:19:41 -0400

Message-ID:

<2008072713194116807-pete@versatilecodingcom>

On 2008-07-27 07:09:48 -0400, Nick Keighley
<nick_keighley_nospam@hotmail.com> said:

On Jul 26, 4:30??pm, Pete Becker <p...@versatilecoding.com> wrote:

On 2008-07-26 10:31:04 -0400, "Andrew Koenig" <a...@acm.org> said:

"Lionel B" <m...@privacy.net> wrote in message
news:g6cub7$k44$7@south.jnrs.ja.net...

You're ok. The *value* of the variable i may well be undefined, but
i is nonetheless an int; and outputting an int - any int, whatever its
value - should never crash your program. Ditto double, etc.

Not true. ??It's not true in theory for int, and definitely not true i

practice for double -- because IEEE floating-point, which most modern
computers use, has a notion of "signaling not-a-number" values that cau

se a

run-time error condition if accessed.

My reading of IEEE-754 is that acessing a signaling NaN causes an
invalid operation exception by default, and the result of that
exception is just to return a quite NaN. Unless the program has
installed a trap handler, this is completely innocuous.

http://blogs.msdn.com/oldnewthing/archive/2008/07/03/8682463.aspx

seems to disagree. Or at least trap handlers seem to get enabled
more easily than you'd think on some OSs

It says that code that your program calls, even if you didn't write it,
can set up trap handlers. That's completely consistent with what I said.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)