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From: gwc@root.co.uk (Geoff Clare)
Newsgroups: comp.lang.c
Subject: NaN's (was Re: FLOATING NULL?)
Message-ID: <2726@root44.co.uk>
Date: 30 May 91 17:18:13 GMT
References: <13223@uhccux.uhcc.Hawaii.Edu> <1991May28.153655.24199@zoo.toronto.edu>
Organization: UniSoft Ltd., London, England
Lines: 13

henry@zoo.toronto.edu (Henry Spencer) writes:

>  If you are willing to constrain your code to run on machines using
>IEEE floating point, you could use a NaN value... but there is no standard
>way of generating such a value or testing for it.

I agree there is no standard way of generating NaN (although sqrt(-1.0)
is your best bet).  However, there is a standard way of testing for NaN.
If x is a floating point variable, then (x != x) will be TRUE if and
only if x has the value NaN.
-- 
Geoff Clare <gwc@root.co.uk>  (Dumb American mailers: ...!uunet!root.co.uk!gwc)
UniSoft Limited, London, England.   Tel: +44 71 729 3773   Fax: +44 71 729 3273