Re: [Boost-users] [Serialization] NVP and xml archives

From: michael mathews (muckjail_at_[hidden])
Date: 2006-11-16 13:00:11

Robert,
Would this be the correct template to modify? I cannot find the
function you mention anywhere. Of course I could be looking in the
wrong places.

//////////////////////////////////////////////////////////////////////
// implementation of serialization for STL containers
//

template<class Archive, class Container>
inline void save_collection(Archive & ar, const Container &s)
{
    // record number of elements
    unsigned int count = s.size();
    ar << make_nvp("count", const_cast<const unsigned int &>(count));
    BOOST_DEDUCED_TYPENAME Container::const_iterator it = s.begin();
    while(count-- > 0){
        //if(0 == (ar.get_flags() &
boost::archive::no_object_creation))
                // note borland emits a no-op without the explicit
namespace
                boost::serialization::save_construct_data_adl(ar,
&(*it), 0U);
        ar << boost::serialization::make_nvp("item", *it++);
    }
}

One more question. The examples say that you should be able to
serialize a list like this:

#include <boost/serialization/list.hpp>

class bus_route
{
    friend class boost::serialization::access;
    std::list<bus_stop *> stops;
    template<class Archive>
    void serialize(Archive & ar, const unsigned int version)
    {
        ar & stops;
    }
public:
    bus_route(){}
};

Does this just work because it is a list of pointers?

Thanks for your help

michael
--- Robert Ramey <ramey_at_[hidden]> wrote:

> and xml_archive requires that ALL elements have a name.  So
> 
> > list< boost::serialization::nvp<V> > sl;
> > ...
> > ar & sl;
> > ...
> 
> would have to be changed to:
> 
> > list< boost::serialization::nvp<V> > sl;
> > ...
> > ar & BOOST_SERIALIZATION_NVP(sl);
> > ...
> 
> which would be OK... But there is one thing you might not like.
> 
> You'll see an extra level tags added by the standard serialization
> of std::list.  These tags have the name "item" - because at
> that level,  there is not way to know what name they should have.
> 
> I'm guessing this would bother you.  In that case you should
> use your own enhanced version of serialization of list items.
> 
> The first thing I would try would be to make
> 
> template<class std::list<boost::nvp<T> > >
> void serialize(boost::archive::xml_archive &ar,
> std::list<boost::nvp<T> 
> const unsigned int version){
>     copy the standard implementation eliminating the NVP("item"...)
> }
> 
> This would be more specialized than the one based on std::list<T> and
> hence
> would take precedence.
> 
> Assuming this gives you what you want, you could then make versions
> for
> all the different collections.  And a separate set for xml_warchive. 
> Slightly
> tedious but a simple process which would solve the problem for
> eternity.
> 
> Just included all the above specializations in my_xml_archive.hpp
> along
> with inclusion of the standard xml_archive.hpp
> 
> Robert Ramey
> 
> michael mathews wrote:
> > Correct I have a list of NVP's. But that is what I need. The idea
> is
> > to have a list of name value pairs where the name is used to
> generate
> > the tag and the value is the value to save. Isn't that how a NVP
> gets
> > serialized to an xml archive?
> >
> > I have also tried
> > list< boost::serialization::nvp<V> > sl;
> > ...
> > ar & sl;
> > ...
> > which I thought would work since the elements of the list are NVP's
> > It also gets caught in the trap.
> >
> > michael
> >
> > --- Robert Ramey <ramey_at_[hidden]> wrote:
> >
> >> This isn't an NVP - its a list of NVPs
> >>
> >> Try
> >>         list<V> sl;
> >>     ...
> >>         ar & BOOST_SERIALIZATION_NVP(sl);
> >>
> >> Robert Ramey
> >>
> >> michael mathews wrote:
> >>> Well I thought it should and I suspect that I am doing something
> >>> silly but this is basically the class I have:
> >>>
> >>>
> >>> template <class N, class V> class test
> >>> {
> >>>    friend class boost::serialization::access;
> >>>    list< boost::serialization::nvp<V> > sl;
> >>>    template<class Archive>
> >>>    void serialize(Archive & ar, const unsigned int version)
> >>>    {
> >>>        ar & BOOST_SERIALIZATION_NVP(sl);
> >>>
> >>>    }
> >>>
> >>> public:
> >>> {
> >>> ...
> >>> }
> >>> and it gets caught in the compile trap
> >>>
> >>> template<class T>
> >>>    void save_override(T & t, BOOST_PFTO int)
> >>>    {
> >>>        // If your program fails to compile here, its most likely
> due
> >>> to
> >>>        // not specifying an nvp wrapper around the variable to
> >>>        // be serialized.
> >>>        BOOST_STATIC_ASSERT(0 == sizeof(T));
> >>>    }
> >>> I thought that a nvp should be serializable automatically.
> >>> Ideas?
> >>> Thanks in advance
> >>> michael
> >>>
> >>> --- Robert Ramey <ramey_at_[hidden]> wrote:
> >>>
> >>>> Doesn't it already do this?
> >>>>
> >>>> Robert Ramey
> >>>>
> >>>> michael mathews wrote:
> >>>>> Hi All,
> >>>>>
> >>>>> I have a class that contains a list of name value pairs . I
> would
> >>>>> like the serialization to use the names for the tag names in
> the
> >>>>> xml archive. Is there a way to do this or do I need to write my
> >>>>> own custom archive?
> >>>>>
> >>>>> Thanks in advance
> >>>>>
> >>>>> Michael
> >>>>>
> >>>>>
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