How to serialize object with shared_ptr member using boost - c++

Question

There are abstract I1 and derived C1.
There are abstract I2 and derived C2.
I1 have shared_ptr<I2>. How can I make them serializable using boost serializaton? I am attemtping do it, but my application get exception.
#include <sstream>
#include <boost/shared_ptr.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>
#include <boost/serialization/shared_ptr.hpp>
struct I1
{
I1() {}
virtual ~I1() = 0 {}
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
}
};
struct C1 : I1
{
virtual ~C1() {}
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & boost::serialization::base_object<I1>(*this);
}
};
struct I2
{
virtual ~I2() = 0 {}
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & p;
}
boost::shared_ptr<I1> p;
};
struct C2 : I2
{
C2() { p = boost::shared_ptr<I1>(new C1); }
virtual ~C2() { }
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & boost::serialization::base_object<I2>(*this);
}
};
int main()
{
C2 c2;
std::string s;
std::stringstream ss(s);
boost::archive::binary_oarchive oa(ss);
oa.register_type<I1>();
oa.register_type<C1>();
oa.register_type<I2>();
oa.register_type<C2>();
oa << c2;
boost::archive::binary_iarchive ia(ss);
//ia.register_type<I1>(); // cannot instantiate abstract class
ia.register_type<C1>();
//ia.register_type<I2>(); // cannot instantiate abstract class
ia.register_type<C2>();
ia >> c2;
}

Answer 1

The boost serialization documentation says here interesting things about BOOST_CLASS_EXPORT:
... BOOST_CLASS_EXPORT ...
Hence, the need for export is implied by the usage of a derived class that is manipulated via a pointer or reference to its base class.
Your p pointer does exactly that. Adding these macros to your code also gets rid of the ugly explicit register_type() calls from your main, which is also nice :)
So, this code seems to compile and work in VS2014:
#include <sstream>
#include <boost/shared_ptr.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>
#include <boost/serialization/shared_ptr.hpp>
#include <boost/serialization/export.hpp>
struct I1
{
I1() {}
virtual ~I1() = 0 {}
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
}
};
BOOST_CLASS_EXPORT(I1)
struct C1 : I1
{
virtual ~C1() {}
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & boost::serialization::base_object<I1>(*this);
}
};
BOOST_CLASS_EXPORT(C1)
struct I2
{
virtual ~I2() = 0 {}
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & p;
}
boost::shared_ptr<I1> p;
};
BOOST_CLASS_EXPORT(I2)
struct C2 : I2
{
C2() { p = boost::shared_ptr<I1>(new C1); }
virtual ~C2() { }
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & boost::serialization::base_object<I2>(*this);
}
};
BOOST_CLASS_EXPORT(C2)
int main()
{
C2 c2;
std::string s;
std::stringstream ss(s);
boost::archive::binary_oarchive oa(ss);
oa << c2;
boost::archive::binary_iarchive ia(ss);
ia >> c2;
}
It is interesting, though, that the statement from Boost docs is obviously not true for all compilers, and lots of code examples on the internets just don't work in VS2014.

Answer 2

I think you aren't supposed to register your pure virtual classes on the output archive either.
Alternatively, you can use export. After defining your classes, replace the rest of your code with this:
#include <boost/serialization/export.hpp>
BOOST_CLASS_EXPORT(C1)
BOOST_CLASS_EXPORT(C2)
int main()
{
C2 c2;
std::string s;
std::stringstream ss(s);
{
boost::archive::binary_oarchive oa(ss);
oa << c2;
}
boost::archive::binary_iarchive ia(ss);
ia >> c2;
}
I put the output archive into a separate block. I think it most likely works without it but I want to be sure that everything is flushed (via going out of scope).

Answer 3

Add
BOOST_SERIALIZATION_ASSUME_ABSTRACT(I1)
BOOST_SERIALIZATION_ASSUME_ABSTRACT(I2)
As per the documentation http://www.boost.org/doc/libs/1_39_0/libs/serialization/doc/traits.html#abstract
UPDATE
I've just verified with VS2013RTM and Boost 1_55, it JustWorks(TM), I've
removed the type registrations for abstract bases (they can never be concretely loaded from the archive anyways)
added
#pragma warning(disable: 4244)
#include <boost/config/warning_disable.hpp>
at the top of the file to silence known chatty warnings
Code compiled and runs without error. For good style, you should probably
serialize c2 through a pointer (stack variables can subtly derail object tracking)
Here's the full code I ended up with:
#pragma warning(disable: 4244)
#include <boost/config/warning_disable.hpp>
#include <sstream>
#include <boost/shared_ptr.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/serialization/shared_ptr.hpp>
struct I1
{
I1() {}
virtual ~I1() = 0 {}
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
}
};
struct C1 : I1
{
virtual ~C1() {}
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & boost::serialization::base_object<I1>(*this);
}
};
struct I2
{
virtual ~I2() = 0 {}
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & p;
}
boost::shared_ptr<I1> p;
};
struct C2 : I2
{
C2() { p = boost::shared_ptr<I1>(new C1); }
virtual ~C2() { }
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & boost::serialization::base_object<I2>(*this);
}
};
int main()
{
boost::shared_ptr<I2> c2(new C2);
std::string s;
std::stringstream ss(s);
boost::archive::text_oarchive oa(ss);
oa.register_type<C1>();
oa.register_type<C2>();
oa << c2;
std::cout << "Serialized form: '" << ss.str() << "'\n";
boost::archive::text_iarchive ia(ss);
ia.register_type<C1>();
ia.register_type<C2>();
ia >> c2;
}
And here's the output: