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

From: Robert Ramey (ramey_at_[hidden])
Date: 2006-11-15 23:20:19

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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