Re: [Boost-users] [serialization] nans and infinite floats in textbased archives...

Subject: Re: [Boost-users] [serialization] nans and infinite floats in textbased archives...
From: François Mauger (mauger_at_[hidden])
Date: 2009-03-08 10:18:03

Hi Robert and all

Thanks for this info. I downloaded the FPU stuff and follow the steps
to use it.
In my library, I use `boost::iostreams::filtering_i/ostream' objects
to dump my text/XML or binary archives.
I have to plug in it resources like
`boost::iostreams::gzip_(de)compressor' or
`boost::iostreams::bzip2_(de)compressor' then `std::i/ofstream' or
`std::cin/cout' (using the `push' method).

My guess is that if I use zipped filtered stream for text/XML archives,
I should not make use of the :

  locale my_locale(default_locale, new nonfinite_num_put<char>);

within the final i/ofstream  as explained in the doc:

  ofstream ofs ("test.txt");
  ofs.imbue (my_locale); // <==== probably wrong
  boost::iostreams::filtering_ostream fos;
  fos.push (boost::iostreams::gzip_compressor ());
  fos.push (ofs);
  boost::archive::text_oarchive oa (fos, no_codecvt);
 ... use oa...

but rather on the `boost::iostreams::filtering_i/ostream' object:

  ofstream ofs ("test.txt");
  boost::iostreams::filtering_ostream fos;
  fos.imbue (my_locale); // <==== probably right
  fos.push (boost::iostreams::gzip_compressor ());
  fos.push (ofs);
  boost::archive::text_oarchive oa (fos, no_codecvt);
  ... use oa...

Am I right?

Also does the order of `imbue' invocation on a stream is important:
Should I use it before or after archive declaration or we don't mind?

  ofstream ofs ("test.txt");
  boost::iostreams::filtering_ostream fos;
  fos.push (boost::iostreams::gzip_compressor ());
  fos.push (ofs);
  boost::archive::text_oarchive oa (fos, no_codecvt);
  fos.imbue (my_locale);
  ... use oa...

thanks again for help
regards
frc

> The serialization library text archives depend upon an underlying
> stream to render output and parse input.  So what is needed
> is a stream that can render NaNs and other such values in
> a portable way.  A library containing such a stream has
> passed review and been accepted into boost.  As far as
> I can tell, it has yet to be checked into the SVN system. The
> version reviewed can be found in the vault:
>
> floating_point_utilities_v3.zip
>
> Hopefully, this can help address your circumstances.
>
> Robert Ramey
>
> François Mauger wrote:
>> Hi serializers, archivers, boosters and Robert,
>>
>> I've used boost:serialization (boost 1.34.1 under Linux ubuntu and/or
>> SL4,, gcc 4.2) for one year. Thanks to this excellent library, our
>> team store critical experimental data (3 TB using zipped text
>> archives).
>>
>> Up to now, I met no problem with text/XML archives as all the
>> stored double values pass the 'isnormal' check.
>>
>> Now my new data analysis programs needs to (de)serialize doubles
>> even if they are NaNs or infinites (for it makes sense for me).
>> Unfortunately, the load method for double fails while reading
>> 'nan' (or 'inf') from the input for this is the standard behavior
>> of the ostream with "! isnormal" doubles.
>>
>> After studying the source code for boost text oriented I/O archives
>> in the hope to find a fix for my problem,
>> I made an attempt to make boost aware of nans and +/-infs in
>> a pragmatic way (I mean trying to save time and storage but keep
>> the information and get rid of the stream error exception).
>> I attached a tiny tarball to show the hack I've done.
>>
>> I'm not sure at all this is be a definitively good and elegant
>> approach to handle nans within text based archives. So I'd appreciate
>> to get some feedback and comments from Robert or any expert in
>> this field. As I work only with Linux, gcc and 1.34.1, this approach
>> is likely not to be portable... but maybe this could initiate
>> some work to fix it in an official way.
>>
>> thanks for your attention and for all this very very
>> useful material.
>>
>> regards
>> frc
>>
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-- 
Francois Mauger
Laboratoire de Physique Corpusculaire de Caen et Universite de Caen
ENSICAEN - 6, Boulevard du Marechal Juin, 14050 CAEN Cedex, FRANCE
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