Re: [Boost-users] [serialization] [units] class_id and class_name to describe quantity dimension in serilization archive

Subject: Re: [Boost-users] [serialization] [units] class_id and class_name to describe quantity dimension in serilization archive
From: Robert Ramey (ramey_at_[hidden])
Date: 2011-09-24 13:08:14

alfC wrote:
> Hi,
> I am serializing a bunch of object that contains boost.units
> quantities. Boost.Units provides serialization for quantities
> already.
> By default, the output file looks ok but I would like to add a class
> name to the object description.
>
> Current, serializing quantity<si::length> q produces:
>
> <q class_id="0" tracking_level="1" version="0" object_id="_0">
>     <value>5</value>
> </q>
>
> Which doesn't give any information about the quantity at hand, not
> even for the human reading it. So, I tried to use
> BOOST_CLASS_EXPORT_GUID to register a name for the serialized class,
> but it is ignored.  Ideally I would like to have something like this,
> with a class_name description for example:
>
> <q class_id="0" class_name = "quantity_si_length" tracking_level="1"
> version="0" object_id="_0">
>     <value>5</value>
> </q>
>
> Is something like this possible? Below is the working code:
>
> #include <fstream>
> #include <boost/serialization/export.hpp>
> #include <boost/archive/text_oarchive.hpp>
> #include <boost/archive/xml_oarchive.hpp>
> #include <boost/units/systems/si/io.hpp>
> using namespace boost::units;
> BOOST_CLASS_EXPORT_GUID(quantity<si::length>, "quantity_si_length")
> //ignored
>
> int main(int argc, char *argv[]) {
>     std::ofstream ofs("filename.xml");
>     boost::archive::xml_oarchive oa(ofs);
>
>     quantity<si::length> q = 5.*si::meter;
>
>     oa << BOOST_SERIALIZATION_NVP(q);
>
>     return 0;
> }
>

This is a feature of the xml_?archive implementation.  In general, the 
archive
implementations include the minimum information required to re-constitute
the original data - and no more.

Robert Ramey