Re: [Boost-users] DeSerialization to update content of objectinsteadof construct new object

From: Matthias Troyer (troyer_at_[hidden])
Date: 2007-05-16 02:16:39

Be careful that this will not work if your base* is a pointer to a  
base class, and you actually want to (de)serialize the derived object.

Matthias

On 16 May 2007, at 13:44, Ng Pan wrote:

> Thank you very much.
> I have successfully overloaded the serialization function. Here is  
> the code
> as the reference for other ppl doing the similar modification.
>
> base.h
>     #ifndef BASE_H
>     #define BASE_H
>     ...
>     #include<boost\serialization\vector.hpp>
>     ...
>     class base
>     {
>        friend class boost::serialization::access;
>        template<class Archive>
>        void serialize(Archive &ar, const unsigned int /*  
> file_version */){
>            ar & BOOST_SERIALIZATION_NVP(m_nID);
>         }
>         .....
>     }
>     ...
>
>      #if defined(__SGI_STL_PORT) || defined(_STLPORT_VERSION)
>      #define STD _STLP_STD
>      #else
>      #define STD std
>     #endif
>
>     namespace boost {
>     namespace serialization {
>
>      //vector<Base *>
>     template<class Archive, class Allocator>
>     inline void save(
>         Archive & ar,
>         const STD::vector<base *, Allocator> &t,
>         const unsigned int /* file_version */
>     ){
>          // record number of elements
>         unsigned int count = t.size();
>         ar << BOOST_SERIALIZATION_NVP(count);
>        for(unsigned int i=0; i< count; i++)
>           ar<<boost::serialization::make_nvp("loaditem", t.at(i));
>      }
>
>      template<class Archive, class Allocator>
>      inline void load(
>          Archive & ar,
>          STD::vector<base *, Allocator> &t,
>           const unsigned int  /*file_version*/
>      ){
>       //   // retrieve number of elements
>           unsigned int count;
>          ar >> BOOST_SERIALIZATION_NVP(count);
>          for(unsigned int i=0; i<count; i++)
> 	ar >> boost::serialization::make_nvp("loaditem", *t.at(i));
>           }
>      }
>      }
>     ...
>    #endif
>
>
> Barr Ng
>
>
>> From: Matthias Troyer <troyer_at_[hidden]>
>> Reply-To: boost-users_at_[hidden]
>> To: boost-users_at_[hidden]
>> Subject: Re: [Boost-users] DeSerialization to update content of
>> objectinsteadof construct new object
>> Date: Wed, 16 May 2007 07:22:28 +1000
>>
>> Another, maybe easier option, could be to  overload the serialization
>> functions for std::vector<base *> .
>>
>> Matthias Troyer
>>
>> On 16 May 2007, at 01:02, Robert Ramey wrote:
>>
>>> The code for serialization of a vector is found in serialization/
>>> vector.hpp.
>>>
>>> I implemented this code to reconstuct the vector items rather than
>>> just reload them.  I did this for a number of reasons - which for
>>> this discussion are not important.
>>>
>>> If this doesn't suit your needs, I would suggest you make your own
>>> version of serialization.hpp which operates differently.  Starting
>>> with the current version it wouldn't be at all hard to do.
>>>
>>> If you want to use both current ("standard") method in some
>>> places in addition to your "custom" method, you might consider
>>> making some sort of wrapper which tags your special
>>> vectors with a type which can be distinguished for special
>>> serialization treatment.
>>>
>>> Robert Ramey
>>>
>>> Ng Pan wrote:
>>>> Hi
>>>>
>>>> I am using boost serialization to synchronise objects between
>>>> different computers (network). The objects would be serializated  
>>>> as a
>>>> string instead of a file by using the class stringstream(instead of
>>>> fstream). The string would be transferred via TCP/IP layer.
>>>>
>>>> Let simpify the situation as only two computers (Master and Slave)
>>>> ,both of two computers have N objects and I wanna synchronise their
>>>> content. I create a vector of pointer ( std::vector<base *>  
>>>> m_vpBase
>>>> ) which points to the dirty objects. Both of two computers have  
>>>> this
>>>> vector. Let assume the vectors are already pointing to the
>>>> corresponding objects. For Tx side, it would serialize the  
>>>> objects as
>>>> a string. For Rx side, I want to update the content of the objects
>>>> that its vector is pointing to.
>>>>
>>>> Tx side:
>>>> oa << BOOST_SERIALIZATION_NVP(m_vpBase);
>>>>
>>>> Rx side:
>>>> oa >> BOOST_SERIALIZATION_NVP(m_vpBase );
>>>>
>>>> However, the above code would construct new objects.
>>>>
>>>> What i want is just update the content of the objects , not  
>>>> construct
>>>> new objects.
>>>>
>>>> I know how to update the content for one object by using pointer (
>>>> base * m_pBase).
>>>> Tx side:
>>>> oa << BOOST_SERIALIZATION_NVP(m_pBase);
>>>>
>>>> Rx side:
>>>> oa >> BOOST_SERIALIZATION_NVP(*m_pBase);
>>>>
>>>>
>>>> But, I don't know how to do for a vector of pointer. If you know,
>>>> please give me some hints. Thank you very much.
>>>>
>>>> Regards
>>>> Barr Ng
>>>> [I found Boost serialization is useful and easy to use. ]
>>>>
>>>> _________________________________________________________________
>>>> No masks required! Use MSN Messenger to chat with friends and  
>>>> family.
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>>>
>>>
>>>
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