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| <title>Template serialization - shared_ptr</title> |
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| <h3><a href="../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../boost.png" border="0"></a></h3> |
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| <td valign="top"> |
| <h1 align="center">Serialization</h1> |
| <h2 align="center"><code style="white-space: normal">shared_ptr<class T></code> Revisited</h2> |
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| The previously described serialization of <code style="white-space: normal">shared_ptr</code> |
| illustrates the straightforward way of serializing a moderately complicated class structure. |
| Unfortunately, this way of doing it suffered from some undesirable features |
| <ul> |
| <li>It was dependent on the Boost implementation of <code style="white-space: normal">shared_ptr</code>. |
| The <code style="white-space: normal">shared_ptr</code> interface has been included |
| in <code style="white-space: normal">std::tr1</code> 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 <code style="white-space: normal">shared_ptr</code>. |
| <li>It required extra macros for export. |
| </ul> |
| |
| <pre><code> |
| 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. |
| ... |
| } |
| </code></pre> |
| |
| In principle, this is very much simpler than the original implementation. Completion of |
| this code requires: |
| |
| <ol> |
| <li>Filling in the "To Do". This required making an extra map for |
| <code style="white-space: normal">shared_ptr</code> instances. |
| <li>A method for identifying pointers to the same objects from pointers to their base classes. |
| <li>Backward compatibility with pointers serialized by the previous method. This exploits |
| the serialization class versioning. |
| <li>Proper handling of <code style="white-space: normal">weak_ptr</code>. |
| </ol> |
| |
| The result of this effort can be found in |
| <a target = serialization_shared_ptr href="../../../boost/serialization/shared_ptr.hpp"> |
| <code style="white-space: normal">boost::serialization::shared_ptr.hpp</code> |
| </a> |
| <p> |
| Note that if your code needs to read archives created under boost version 1.32, you will |
| have to include the following |
| |
| <pre><code> |
| #include <boost/serialization/shared_ptr_132.hpp> |
| #include <boost/serialization/shared_ptr.hpp> |
| </code></pre> |
| rather than just |
| <pre><code> |
| #include <boost/serialization/shared_ptr.hpp> |
| </code></pre> |
| |
| <hr> |
| <p><i>© Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 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) |
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