[Boost-users] [serialization] Serialization of derived classes

From: Christian Henning (chhenning_at_[hidden])
Date: 2006-10-23 10:25:59

Hi there, I'm having problems when serializing derived classes from a
non-polymorphic base class. I have read the section "Pointers to
Objects of Derived Classes". But for some reasons I cannot make these
tricks to work in my application. I have created a small sample
application that shows my problem:

class base
{
public:
   base() : _type( 0 ) {}
   base( unsigned int type) : _type( type ) {}

   unsigned int type() { return _type; }
private:

   friend boost::serialization::access;

   template< class ARCHIVE >
   void serialize( ARCHIVE& ar, const unsigned int version )
   {
      ar & _type;
   }

private:

   unsigned int _type;
};

class derived1 : public base
{
public:
   derived1() : base( 1 ), _value( 2.1 ) {}

private:

   friend boost::serialization::access;

   template< class ARCHIVE >
   void serialize( ARCHIVE& ar, const unsigned int version )
   {
      ar & boost::serialization::base_object<base>( *this );
      ar & _value;
   }

private:

   double _value;
};

class derived2 : public base
{
public:
   derived2() : base( 2 ), _value( 8 ) {}

private:

   friend boost::serialization::access;

   template< class ARCHIVE >
   void serialize( ARCHIVE& ar, const unsigned int version )
   {
      ar & boost::serialization::base_object<base>( *this );
      ar & _value;
   }

private:

   short _value;
};

BOOST_CLASS_EXPORT( derived1 );
BOOST_CLASS_EXPORT( derived2 );

int _tmain(int argc, _TCHAR* argv[])
{
   std::string data;

   {
      std::ostringstream archive_stream;
      boost::archive::binary_oarchive archive( archive_stream );

      derived2 d;
      archive & d;

      data = archive_stream.str();
   }

   {
      // deserialize
      std::string archive_data( &data[0], data.size() );
      std::istringstream archive_stream( archive_data );
      boost::archive::binary_iarchive archive( archive_stream );

      // I don't know what derived class was serialized.
      base* b;
      archive & b;

      if( b->type() == 1 )
      {
         derived1* d1 = static_cast<derived1*>( b );
      }
      else
      {
         derived2* d2 = static_cast<derived2*>( b );
      }
   }

        return 0;
}

Any help is more than welcome.

Thanks ahead,
Christian