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| 3 | <!-- |
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| 4 | (C) Copyright 2002-4 Robert Ramey - http://www.rrsd.com . |
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| 5 | Use, modification and distribution is subject to the Boost Software |
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| 6 | License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
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| 7 | http://www.boost.org/LICENSE_1_0.txt) |
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| 8 | --> |
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| 9 | <head> |
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| 10 | <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> |
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| 11 | <link rel="stylesheet" type="text/css" href="../../../boost.css"> |
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| 12 | <link rel="stylesheet" type="text/css" href="style.css"> |
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| 13 | <title>Template serialization - shared_ptr</title> |
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| 14 | </head> |
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| 15 | <body link="#0000ff" vlink="#800080"> |
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| 16 | <table border="0" cellpadding="7" cellspacing="0" width="100%" summary="header"> |
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| 17 | <tr> |
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| 18 | <td valign="top" width="300"> |
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| 19 | <h3><a href="../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../boost.png" border="0"></a></h3> |
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| 20 | </td> |
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| 21 | <td valign="top"> |
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| 22 | <h1 align="center">Serialization</h1> |
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| 23 | <h2 align="center"><code style="white-space: normal">shared_ptr<class T></code> Revisted</h2> |
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| 24 | </td> |
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| 25 | </tr> |
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| 26 | </table> |
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| 27 | <hr> |
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| 28 | The previously described serialization of <code style="white-space: normal">shared_ptr</code> |
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| 29 | illustrates the straightforward way of serializing a moderately complicated class structure. |
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| 30 | Unfortunately, this way of doing it suffered from some undesirable features |
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| 31 | <ul> |
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| 32 | <li>It was dependent on the Boost implementation of <code style="white-space: normal">shared_ptr</code>. |
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| 33 | The <code style="white-space: normal">shared_ptr</code> interface has been included |
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| 34 | in <code style="white-space: normal">std::tr1</code> and may someday be included in the standard |
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| 35 | C++ library. An implementation which depends only on the public interface can be guarenteed to |
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| 36 | function with any other future implementation of <code style="white-space: normal">shared_ptr</code>. |
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| 37 | <li>It required extra macros for export. |
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| 38 | </ul> |
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| 39 | |
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| 40 | <pre><code> |
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| 41 | template<class Archive, class T> |
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| 42 | inline void save( |
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| 43 | Archive & ar, |
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| 44 | const boost::shared_ptr<T> &t, |
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| 45 | const unsigned int /* file_version */ |
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| 46 | ){ |
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| 47 | const T * t_ptr = t.get(); |
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| 48 | // just seriailize the underlying raw pointer |
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| 49 | ar <<: boost::serialization::make_nvp("px", t_ptr); |
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| 50 | } |
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| 51 | |
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| 52 | template<class Archive, class T> |
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| 53 | inline void load( |
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| 54 | Archive & ar, |
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| 55 | boost::shared_ptr<T> &t, |
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| 56 | const unsigned int file_version |
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| 57 | ){ |
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| 58 | T* r; |
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| 59 | // recover the underlying raw poiter |
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| 60 | ar >> boost::serialization::make_nvp("px", r); |
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| 61 | |
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| 62 | // To Do - match up with other shared pointers which |
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| 63 | // use this same raw pointer. |
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| 64 | ... |
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| 65 | } |
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| 66 | </code></pre> |
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| 67 | |
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| 68 | In priniciple this is very much simpler than the original implementation. Completion of |
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| 69 | this code requires: |
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| 70 | |
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| 71 | <ol> |
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| 72 | <li>Filling in the "To Do". This required making an extra map for |
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| 73 | <code style="white-space: normal">shared_ptr</code> instances. |
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| 74 | <li>A method for identifing pointers to the same objects from pointers to their base classes. |
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| 75 | <li>Backward compatibility with pointers serialized by the previous method. This exploits |
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| 76 | the serialization class versioning. |
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| 77 | <li>Proper handling of <code style="white-space: normal">weak_ptr</code>. |
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| 78 | </ol> |
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| 79 | |
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| 80 | The result of this effort can be found in |
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| 81 | <a target = serialization_shared_ptr href="../../../boost/serialization/shared_ptr.hpp"> |
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| 82 | <code style="white-space: normal">boost::serialization::shared_ptr.hpp</code> |
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| 83 | </a> |
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| 84 | <p> |
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| 85 | Note that if your code needs to read archives created under boost version 1.32, you will |
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| 86 | have to include the following |
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| 87 | |
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| 88 | <pre><code> |
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| 89 | #include <boost/serialization/shared_ptr_132.hpp> |
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| 90 | #include <boost/serialization/shared_ptr.hpp> |
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| 91 | </code></pre> |
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| 92 | rather than just |
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| 93 | <pre><code> |
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| 94 | #include <boost/serialization/shared_ptr.hpp> |
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| 95 | </code></pre> |
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| 96 | |
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| 97 | <hr> |
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| 98 | <p><i>© Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 2002-2004. |
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| 99 | Distributed under the Boost Software License, Version 1.0. (See |
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| 100 | accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
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| 101 | </i></p> |
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| 102 | </body> |
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| 103 | </html> |
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