###

# Serialization

## `shared_ptr<class T>` Revisited

The previously described serialization of `shared_ptr` illustrates the straightforward way of serializing a moderately complicated class structure. Unfortunately, this way of doing it suffered from some undesirable features

- It was dependent on the Boost implementation of `shared_ptr`. The `shared_ptr` interface has been included in `std::tr1` and may someday be included in the standard C++ library. An implementation which depends only on the public interface can be guaranteed to function with any other future implementation of `shared_ptr`.
- It required extra macros for export.

    template<class Archive, class T>
    inline void save(
        Archive & ar,
        const boost::shared_ptr<T> &t,
        const unsigned int /* file_version */
    ){
        const T * t_ptr = t.get();
        // just serialize the underlying raw pointer
        ar << boost::serialization::make_nvp("px", t_ptr);
    }

    template<class Archive, class T>
    inline void load(
        Archive & ar,
        boost::shared_ptr<T> &t,
        const unsigned int file_version
    ){
        T* r;
        // recover the underlying raw pointer
        ar >> boost::serialization::make_nvp("px", r);

        // To Do - match up with other shared pointers which
        // use this same raw pointer.
        ...
    }

In principle, this is very much simpler than the original implementation. Completion of this code requires:

1. Filling in the "To Do". This required making an extra map for `shared_ptr` instances.
2. A method for identifying pointers to the same objects from pointers to their base classes.
3. Backward compatibility with pointers serialized by the previous method. This exploits the serialization class versioning.
4. Proper handling of `weak_ptr`.

The result of this effort can be found in `boost::serialization::shared_ptr.hpp`

Note that if your code needs to read archives created under boost version 1.32, you will have to include the following

    #include <boost/serialization/shared_ptr_132.hpp>
    #include <boost/serialization/shared_ptr.hpp>

rather than just

    #include <boost/serialization/shared_ptr.hpp>

© Copyright Robert Ramey 2002-2004. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)