Re: Unknown #INFO

[davidf(at)dfanning.com (David Fanning)]

Hi Folks,

Here is a recent e-mail sent to me and posted with his
permission from someone who *absolutely* knows what is 
going on here with this NAN business:

> Different operating systems use different representations for
> Nan and Infinity. Some, like Windows or HP-UX are quite bizzare, and not all
> can be output and then input successfully, even on the platform that produces
> them. This is all a function of the standard C library (stdio) on the given
> platform. It has always been thus...
> 
> For IDL 5.2, I pulled the reading and writing of this stuff into IDL
> code rather than leaving it to the stdio on the target platform. That
> accounts for the pleasing consistency that you've observed in IDL 5.2Beta.
> There is a new keyword to PRINT and STRING (STDIO_NON_FINITE) that overrides
> this and allows the stdio to produce the native output. I don't expect many 
> people to use this keyword, but it's there in case you have some other
> program on a given platform that understands (for example) "1.#INFO"
> but not "Infinity".
> 
> I also made IDL on input understand all the various odd platform specific
> representations for this, so you can read a "1.#INFO" produced on a
> Windows box on other platforms (like say, Solaris) without any extra effort.
> 
> A related improvement is that the FINITE function has new keywords
> ("INFINITY" and "NAN") to make dedecting them in a cross platform way
> easier.
> 
> There's a section on this stuff in the "What's New" book, but most people
> have not seen it yet.

Cheers,

David

----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438, Toll-Free Book Orders: 1-888-461-0155
Coyote's Guide to IDL Programming: http://www.dfanning.com/