Re: [boost] Report from Berlin C++ Standards Committee meeting

From: Paul A Bristow (pbristow_at_[hidden])
Date: 2006-04-20 06:04:45

| -----Original Message-----
| From: boost-bounces_at_[hidden] 
| [mailto:boost-bounces_at_[hidden]] On Behalf Of Jeff Garland
| Sent: 20 April 2006 04:01
| To: boost_at_[hidden]
| Subject: Re: [boost] Report from Berlin C++ Standards 
| Committee meeting
| 
| On Wed, 19 Apr 2006 18:31:14 +0100, Paul A Bristow wrote
| 
| > So a) is in principle fixed IMO.
| > 
| > As to b), I had understood that we had agreed that all NaNs 
| could reasonably
| > be treated as identical and one would get a NaN (unspecified) back.
| > Similarly infinities.
| > 
| > 
| http://article.gmane.org/gmane.comp.lib.boost.devel/134569/mat
| ch=serializati
| > on+nan
| > 
| > But simple
| > 
| > 	stream << output_value; // write out.
| > 	double read_value;
| > 	stream >> read_value; // read back.
| > 
| > doesn't work for
| > 
| > double output_value = numeric_limits<double>::quiet_NaN(); 
| // output_value
| > 1.#QNAN != read_value 1
| > double output_value = numeric_limits<double>::infinity(); 
| // output_value
| > 1.#INF != read_value 1
| > 
| > So some special flag would be needed to hold the Nan or Inf nature.
| > 
| > If only there was a Standard representation of Nan and Infs.  VERY
| > shortsighted, making NaNs and infs hardly useable.
| 
| Agreed.  The types in date_time have the ability to serialize 
| and deserilize
| NADT (not a date time), -infinity and +infinity.  Why 
| couldn't there be a
| simple extension to the numpunct<charT> facet to define an 
| appropriate output
| string?  Basically something like:
| 
|   //see Langer and Kreft p 414...
|   template<class charT>
|   class numpunct : public locale::facet {
|   
|     //new functions for nan and infinity
|     string_type not_a_number_name() const;  
|     string_type infinity_name()     const;  
| 
| And you'd have to fix num_get as well.

Looks a good idea - but these facets look complicated to my inexpert eye.

Should we ALSO press to get a 'proper' C++0x Standard solution to this?

Paul

-- 
Paul A Bristow
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