Re: [Boost-users] [serialization] deriving from xml_iarchive

Subject: Re: [Boost-users] [serialization] deriving from xml_iarchive
From: Kenny Riddile (kfriddile_at_[hidden])
Date: 2009-04-20 11:54:02

That's similar to what I've tried, but I am not allowed to directly 
modify boost headers or source files...

Robert Ramey wrote:
> OK- here goes:
> 
> 
> a) make your own class my_helper and put it into a header file
> b) start with boost/archive/xml_iarchive.hpp
> c) where it says #include <boost/archive/shared_ptr_helper.hpp>
> add another line "#include "my_helper"
> d) where it says public detail::shared_ptr_helper
> add ", my_helper
> e) recompile xml_iarchive.cpp
> 
> good luck,
> 
> Robert Ramey
> 
> Kenny Riddile wrote:
>> Both me and another dev have read all the relevant
>> documentation/examples and still can't make this work.  Would it be
>> possible to get a simple example...maybe an input archive that behaves
>> exactly like xml_iarchive and lets you pass an additional int to the
>> constructor and retrieve it later via something like
>> myArchive.GetStoredInt() ?
>>
>> Robert Ramey wrote:
>>> I think the best way to handle this is by making an archive helper.
>>>
>>> If you look into the implemenation of ..._oarchive, you'll see that
>>> it looks something like the following:
>>>
>>>
>>> class xml_oarchive : public naked_xml_oarchive, shared_ptr_helper
>>> {... This is to implement special facility for shared_ptr which would
>>> otherwise not be serializable. (note: this is the only case where
>>> the archive classes address issues related to the implemenation
>>> of a particular type).
>>>
>>> You could do something similar for your own "special" type.
>>>
>>> Look in the documentaion under "case studies" for a
>>> more complete explanation.
>>>
>>> Robert Ramey
>>>
>>> Kenny Riddile wrote:
>>>> I have a situation where I want an additional piece of data to be
>>>> owned by the archive type we're using.  Previously, I had this
>>>> typedef that's used throughout our code:
>>>>
>>>>     typedef boost::archive::xml_iarchive IutputArchive;
>>>>
>>>> I changed it to something like this:
>>>>
>>>>     class InputArchive : public boost::archive::xml_iarchive
>>>>     {
>>>>     public:
>>>>         InputArchive( std::istream& is, Foo bar )
>>>>             : boost::archive::xml_iarchive( is )
>>>>             , m_bar( bar )
>>>>
>>>>         Foo GetFoo() const
>>>>         {
>>>>             return m_bar;
>>>>         }
>>>>
>>>>     private:
>>>>         Foo m_bar;
>>>>     };
>>>>
>>>> The problem I'm seeing is that whenever a serializable class's
>>>> serialize() method is invoked via an InputArchive object, the
>>>> template parameter to serialize() is instantiated with
>>>> boost::archive::xml_iarchive, not InputArchive, which I need.  Is it
>>>> possible to get the behavior I want through public derivation like
>>>> this, or is there a better way?