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

From: Jeff Garland (jeff_at_[hidden])
Date: 2006-04-19 23:01:15

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/match=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.

Jeff