Re: [Boost-users] Boost.Serialization: Restoring object state (preventcreation of a new object)?

Subject: Re: [Boost-users] Boost.Serialization: Restoring object state (preventcreation of a new object)?
From: Robert Ramey (ramey_at_[hidden])
Date: 2010-08-30 12:11:18

ray_at_[hidden] wrote:

If an object is serialized (saved) from a pointer, the loading part automatically creates (instantiates) a new object. However, there are situations when the object is already created and all we need is to restore its state.

The following code demonstrates one possible - although not elegant - solution using a temporary object:

#include <fstream>#include <iostream>#include <boost/archive/xml_iarchive.hpp>#include <boost/archive/xml_oarchive.hpp>#include <boost/serialization/string.hpp>#include <boost/serialization/export.hpp>class A{public:    A()    : m_val(100)    {    }        int m_val;private:    friend class boost::serialization::access;    template <typename Archive>    void serialize(Archive &ar, const unsigned int version)    {        ar & BOOST_SERIALIZATION_NVP(m_val);    }};int main(int argc, char* argv[]){    A *a = new A();        // Save the object    {        std::ofstream os("d:/test.xml");        boost::archive::xml_oarchive oa(os);        // Save from pointer        oa & BOOST_SERIALIZATION_NVP(a);    }        // Change the object state    a->m_val = 200;    // Restore the state    {        std::ifstream is("d:/test.xml");        boost::archive::xml_iarchive ia(is);                A* aTemp;        ia & BOOST_SERIALIZATION_NVP(aTemp);        a->m_val = aTemp->m_val; // Copy object state        assert(a->m_val == 100);        delete aTemp;    }}Just avoid serialization through a pointer, serialize either theobject or a reference to the object.change the above to:    A a;        // Save the object    {        std::ofstream os("d:/test.xml");        boost::archive::xml_oarchive oa(os);        // Save from pointer        oa & BOOST_SERIALIZATION_NVP(a);    }        // Change the object state    a->m_val = 200;    // Restore the state    {        std::ifstream is("d:/test.xml");        boost::archive::xml_iarchive ia(is);                ia & BOOST_SERIALIZATION_NVP(aTemp);        ar >> a // Copy object state        assert(a->m_val == 100);        delete aTemp;    }Robert Ramey