Re: [Boost-users] [serialization] infinite floating point values

From: Johan Råde (rade_at_[hidden])
Date: 2006-07-04 12:12:34

I agree. This has nothing to with the serialization lib.
I will use the solution that you suggest.
Thanks for the help.

--Johan Råde

Robert Ramey wrote:
> This was the subject of some discussion.  Its not really an issue
> with the serialization library itself as it is for stream i/o in
> general.  After looking into this, it became apparent that
> that
> 
> a) there is no agreed upon set of NaN types for all compilers.
> b) there is no general way to create a specific type of NaN
> c) other reasons I prefer not to go into here.
> 
> But the good news is that its pretty easy to address for anyone
> who needs this functionality.
> 
> Solution:
> 
> a) create your own numput facets for input and output text streams.
> ideally there would be a couple of these facets.
> i) numput_strick - traps whenever a NaN is saved.  This would
> support the view that no NaN's are expected in the output/input and
> would trap attempts to use them in this context.
> ii)numput_flakey - translates NaNs to/from some portable indicator
> and attempts to recreate the same type of NaN from the indicator.
> 
> Usage:
> a) create a stream you're interested in - from fstream or whatever.
> b) pick the numput facet which implements the desired behavior
> and attach it to the stream
> c) pass the stream object to the text_archive upon opening.
> 
> This approach would have a couple of advantages.
> 
> a) it lets different users use thier own preferred way of handling
> this.
> b) it is useful beyond the serialization library.
> c) it leverages on known patterns and practices of the standard
> stream i/o
> d) its not that hard to do.
> e) it doesn't require messing with the serialization library.
> 
> Although the topic incited a lot of interest - but not enough
> for anyone to actually to do the work to make such stream facets.
> 
> Robert Ramey
> 
> Johan Råde wrote:
>> I just replaced the binary archives by text archives in an app,
>> to make sure that the archives will be portable between 32 and 64 bit
>> platforms.
>> But when I use text archives, the app crashes.
>> The problem is:
>>
>> Text archives do not handle infinite values of type float and double.
>>
>> --- Example ----------------------------------------------------------
>>
>> #include <iostream>
>> #include <limits>
>> #include <sstream>
>> #include <boost/archive/text_iarchive.hpp>
>> #include <boost/archive/text_oarchive.hpp>
>> #include <boost/format.hpp>
>>
>> int main()
>> {
>>      std::stringstream ss;
>>
>>      {
>>          boost::archive::text_oarchive oa(ss);
>>          double inf1 = std::numeric_limits<double>::infinity();
>>          std::cout << boost::format("Save: %1%\n") % inf1;
>>          oa << inf1;
>>      }
>>
>>      {
>>          boost::archive::text_iarchive ia(ss);
>>          double inf2;
>>          ia >> inf2;
>>          std::cout << boost::format("Load: %1%\n") % inf2;
>>      }
>> }
>>
>> --- Output ----------------------------------------------------------
>>
>> Save: 1.#INF
>> Load: 1
>>
>> ---------------------------------------------------------------------
>>
>> There are two infinite values of type double,
>>      std::numeric_limits<double>::infinity()
>> and
>>      -std::numeric_limits<double>::infinity().
>> These could be represented as "inf" and "-inf" in the archive.
>>
>> I would be very useful for me if this functionality
>> were added to the serialization library.
>> (Otherwise I will have to do a lot of code rewriting,
>> or stick binary archives.)
>>
>> One could also consider handling nan (not a number),
>> but that is maybe a lower priority.
>>
>> --Johan Råde
>>
>> rade_at_[hidden] 
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users