[Boost-users] implementation of serialization code cannot be done in cpp file

From: Cheok Yan Cheng (yccheok_at_[hidden])
Date: 2006-08-10 05:06:17

I am using VC++ 2003. I realize that when I provide
the code defination for save and load on cpp file, the
following error will occur:

animal error LNK2019: unresolved external symbol
"private: void __thiscall cat::save<class
boost::archive::text_oarchive>(class
boost::archive::text_oarchive &,unsigned int)const "
(??$save_at_Vtext_oarchive_at_archive@boost@@@cat@@ABEXAAVtext_oarchive_at_archive@boost@@I_at_Z)
referenced in function "public: static void __cdecl
boost::serialization::access::member_save<class
boost::archive::text_oarchive,class cat const >(class
boost::archive::text_oarchive &,class cat const
&,unsigned int)"
(??$member_save_at_Vtext_oarchive_at_archive@boost@@$$CBVcat@@@access_at_serialization@boost@@SAXAAVtext_oarchive_at_archive@2_at_ABVcat@@I_at_Z)

------
cat.h
------
#ifndef CAT_H
#define CAT_H

#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>

class cat
{
private:
    friend class boost::serialization::access;
    template<class Archive>
    void save(Archive & ar, const unsigned int
version) const;
    template<class Archive>
    void load(Archive & ar, const unsigned int
version);
    BOOST_SERIALIZATION_SPLIT_MEMBER()
};

#endif

-------
cat.cpp
-------
#include "cat.h"

template<class Archive>
void cat::save(Archive & ar, const unsigned int
version) const
{
}

template<class Archive>
void cat::load(Archive & ar, const unsigned int
version)
{
}

--------
main.cpp
--------
#include <iostream>
#include <cassert>
#include <string>
#include <sstream>
#include <fstream>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include "cat.h"

int main()
{
    const cat c;

    // make an archive
    std::ofstream ofs("test");
    boost::archive::text_oarchive oa(ofs);
    oa << c;
}

However, if I remove cat.cpp file during compilation
and having the code defination at header file as
follow, the code compiled with no problem. May I know
how I can put my serialization code at cpp file
instead of header file? Thank you very much! 

The reason I want to do so is that I need to perform
class forwarding in certain classes. Due to the reason
class forwarding unable to provide a full information
of a class at header level, serialization code can
only be written in cpp file level.

------
cat.h
------
#ifndef CAT_H
#define CAT_H

#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>

class cat
{
private:
    friend class boost::serialization::access;
    template<class Archive>
    void save(Archive & ar, const unsigned int
version) const{}
    template<class Archive>
    void load(Archive & ar, const unsigned int
version) {}
    BOOST_SERIALIZATION_SPLIT_MEMBER()
};

#endif

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