Re: [Boost-users] XML Serialization Traits Question

From: William Bardon (wbardon_at_[hidden])
Date: 2006-07-26 17:50:27

Robert,

Thanks for the example; it helped clear up some uncertainty about the
template arguments in the derived class. 

Regarding save_override, I see where specialized versions for the
different trait types are defined in basic_xml_oarchive.ipp.  I also see
that save_override is called from the operator<< redefinition in
interface_oarchive.hpp.  What I'm missing is the link between
serializing a user-defined class object and the traits of that object.  

template<class Archive>
BOOST_ARCHIVE_OR_WARCHIVE_DECL(void)
basic_xml_oarchive<Archive>::save_override(const version_type & t, int)
{
    int i = t.t; // extra .t is for borland
    write_attribute(VERSION(), i);
}

This function already displays a version attribute in the XML.  How do I
make sure this is called for every element?  I'm sorry, but I can't
figure out how to modify chain of control to force output of class
traits.

Starting in oserializer.hpp, boost::archive::save<Archive,T> calls
static save_non_pointer_type<Archive, T>::invoke calls
serialize_adl calls
boost::serialization::serialize<Archive, T> calls
access::serialize calls 
myClass::serialize<Archive> (Archive& ar, unsigned int version)

There is also a function oserializer<Archive,T>::save_object_data that
calls serialize_adl, but I can't find anything that calls it.

The struct save_non_pointer_type<Archive, T> in oserializer.hpp may be
the key, but I'm not sure how it works.

In oserializer.hpp, struct
save_non_pointer_type<Archive,T>::save_standard::invoke calls
Archive::save_object, but I do not see an implementation of the function
anywhere:

$ find /usr/include/boost -type f -exec grep -H save_object {} \;| grep
-v save_object_ | more
/usr/include/boost/archive/polymorphic_oarchive.hpp:    virtual void
save_object(
/usr/include/boost/archive/detail/oserializer.hpp:
ar.save_object(& t, oserializer<Archive, T>::instantiate());
/usr/include/boost/archive/detail/basic_oarchive.hpp:    void
save_object(
/usr/include/boost/archive/detail/polymorphic_oarchive_impl.hpp:
virtual void save_object(
/usr/include/boost/archive/detail/polymorphic_oarchive_impl.hpp:
ArchiveImplementation::save_object(x, bos);

I'd appreciate any suggestions.  Am I even looking in the right place?

Thanks in advance,
Bill

-----Original Message-----
From: boost-users-bounces_at_[hidden]
[mailto:boost-users-bounces_at_[hidden]] On Behalf Of Robert Ramey
Sent: Wednesday, July 26, 2006 12:14 PM
To: boost-users_at_[hidden]
Subject: Re: [Boost-users] XML Serialization Traits Question

"William Bardon" <wbardon_at_[hidden]> wrote in message
news:C73E689C9FCF884B9A550ECFADA0721C087D3E_at_exchange.cab-cds.org...
I have read both the Boost Serialization online documentation and the
archives of the Boost-Users mailing list looking for guidance, but I
haven't found anything relevant.  I see how to use BOOST_CLASS_TRACKING
and BOOST_CLASS_IMPLEMENTATION to remove version tracking attributes
from the XML tags.

Usage of these macros does a lot more than remove attributes from the
tags.

I want to go in the opposite direction.  I notice that the class_id and
version attributes only appear the first time an object of a particular
class is serialized.  I want to force the version attribute to appear in
every object's attribute list.

Do I need to derive a custom archive to do this?

yes

I have looked at the source code for serialization, but I have trouble
plowing through all of the macros, template expansions, and overloaded
functions to locate the specific part that controls whether class traits
are stored as attributes in a particular XML tag.

I sympathize - its hard to follow.  And I wrote it.  Here are some
hints:

a) look at demo_fast_archive.cpp to see a model of how one can derive
from an existing archive.
b) You'll want to derive from xml_oarchive_impl<...> to create
my_xml_oarchive
c) add a "save_override" function to my_xml_oarchive which replaces the
"save_override" function in
    basic_xml_oarchive.ipp.  Implement this using functions defined
basic_xml_oarchive.ipp

Good luck -

Robert Ramey

Thanks in advance,
Bill

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