Re: [Boost-users] [Serialization] Problem serializingviabaseclassptr

8 Aug 2006

      Hello Robert,

Just to let you know that everything works fine now.  Thanks for your help,

Guy

-----Original Message-----
From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Robert Ramey
Sent: Monday, August 07, 2006 1:18 PM
To: boost-users@lists.boost.org
Subject: Re: [Boost-users] [Serialization] Problem serializingviabaseclassptr

Guy Létourneau wrote:
...
Hello Robert,
Sorry for not giving you feedback earlier, I was on vacation.  I've
included your proposed changes in my test application but I still get
the same compile error:
C:/Boost/include/boost-1_33_1/boost/archive/detail/oserializer.hpp:
In function `void boost::archive::save(Archive&, T&) [with Archive =
boost::archive::text_oarchive, T = const A*]':
C:/Boost/include/boost-1_33_1/boost/archive/basic_text_oarchive.hpp:78:
instantiated from `void
boost::archive::basic_text_oarchive<Archive>::save_override(T&, int)
[with T = const A*, Archive = boost::archive::text_oarchive]'
C:/Boost/include/boost-1_33_1/boost/archive/detail/interface_oarchive.hpp:78:
instantiated from `Archive&
boost::archive::detail::interface_oarchive<Archive>::operator<<(T&)
[with T = const A*, Archive = boost::archive::text_oarchive]'
../main.cpp:101:   instantiated from here
C:/Boost/include/boost-1_33_1/boost/archive/detail/oserializer.hpp:567:
error: incomplete type `boost::STATIC_ASSERTION_FAILURE<false>' does
not have member `value'
make: *** [main.o] Error 1
Could you tell me what I'm missing?
Thanks again for your help,
Guy Letourneau
Test application:
#include <iostream>
#include <fstream>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/serialization/export.hpp>
class A
{
   public:
A()
       {
           i = 1;
       };
virtual ~A()
       {
       };
virtual void Dummy() = 0;
private:
int i;
friend
       class boost::serialization::access;
template <class Archive>
       void serialize( Archive& ar, const unsigned int version )
       {
           std::cout << "Serialization of A" << std::endl;
           std::cout.flush();
       }
};
BOOST_IS_ABSTRACT(A)
class B : public A
{
   public:
B()
       {
       };
virtual ~B()
       {
       };
void Dummy()
       {
       };
void SetValue( std::string& value )
       {
           Data = value;
       }
private:
friend
       class boost::serialization::access;
template <class Archive>
       void serialize( Archive& ar, const unsigned int version )
       {
           ar & boost::serialization::base_object<A>( *this );
           ar & Data;
           std::cout << "Serialization of B" << std::endl;
           std::cout.flush();
       }
std::string Data;
};
BOOST_CLASS_EXPORT(B)
int main()
{
   // Create a B object
   B* Child = new B;
// Set some data
   std::string Data = "test";
   Child->SetValue( Data );
// Assign it to a A ptr
****
// >    const A* Parent = Child; // Parent is now const
// nope- Parent is not const - it points to a const A - not the same thing 
!!!
// try

    const A * const Parent = Child; // const pointer to a const A

// also the following will work - I believe

    A * const Parent = Child;
...
// create and open a character archive for output
   std::ofstream ofs( "filename" );
// save data to archive
   {
       try
       {
           boost::archive::text_oarchive oa( ofs );
           // write class instance to archive
           oa << Parent; // Ptr dereferencing is performed by the
       library }
       catch( boost::archive::archive_exception& e )
       {
           std::cout << "Save failed! : " << e.what();
           std::cout.flush();
return false;
       }
       catch( ... )
       {
           std::cerr << "Unknown Exception " << std::endl;
return false;
       }
// archive and stream closed when destructors are called
   }
delete Child;
}
-----Original Message-----
From: boost-users-bounces@lists.boost.org
[mailto:boost-users-bounces@lists.boost.org] On Behalf Of Robert
Ramey
Sent: Saturday, July 22, 2006 6:43 PM
To: boost-users@lists.boost.org
Subject: Re: [Boost-users] [Serialization] Problem
serializingviabaseclassptr
Three show stopping problems in this code:
a) A doesn't have serialize method even though
such a method is invoked by base object. see:
http://www.boost.org/libs/serialization/doc/serialization.html
b) saving a non-const object - see rationale section
c) Main show stopper:
...
int main()
{
    // Create a B object
    B* Child = new B;
// Set some data
    std::string Data = "test";
    Child->SetValue( Data );
// Assign it to a A ptr
    // const A* Parent = Child;  // ****** note new const - see
rationale
// create and open a character archive for output
    std::ofstream ofs( "filename" );
// save data to archive
    {
        try
        {
            boost::archive::text_oarchive oa( ofs );
            // write class instance to archive
              // *** big problem here.  Dereferecing pointer to A
yields a
ref
              // *** to an A - regardless that ptr was a B.  What you
really want is:
               oa << Parent; // *** let serialization handle
               dererencing // *** instead of:
            //oa << *Parent;
        }
        catch( boost::archive::archive_exception& e )
        {
            std::cout << "Save failed! : " << e.what();
            std::cout.flush();
return false;
        }
        catch( ... )
        {
            std::cerr << "Unknown Exception " << std::endl;
return false;
        }
// archive and stream closed when destructors are called
    }
delete Child;
}
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Guy Létourneau

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