Re: [Boost-users] implementation of serialization code cannot be donein cpp file

From: Robert Ramey (ramey_at_[hidden])
Date: 2006-08-10 10:51:28

This looks to be a C++ code instantiation issue.

Lookup explicit instantiation in your C++ reference.

Look at the demo - polymorphic archives which
tests separate code compilation.

Good Luck

Robert Ramey

Cheok Yan Cheng wrote:
> 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)
> {
> }
>

*** try adding the following here
#include <boost/archive/text_iarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
// explicit instantiation
template cat::save(boost::archive::text_oarchive ar, const unsigned int 
version) const;
template cat::load(boost::archive::text_oarchive 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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