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| 13 | <title>Serialization - Tutorial</title> |
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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">Tutorial</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 | <dl class="page-index"> |
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| 29 | <dt><a href="#simplecase">A Very Simple Case</a> |
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| 30 | <dt><a href="#nonintrusiveversion">Non Intrusive Version</a> |
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| 31 | <dt><a href="#serializablemembers">Serializable Members</a> |
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| 32 | <dt><a href="#derivedclasses">Derived Classes</a> |
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| 33 | <dt><a href="#pointers">Pointers</a> |
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| 34 | <dt><a href="#arrays">Arrays</a> |
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| 35 | <dt><a href="#stl">STL Collections</a> |
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| 36 | <dt><a href="#versioning">Class Versioning</a> |
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| 37 | <dt><a href="#splitting">Splitting <code style="white-space: normal">serialize</code> into <code style="white-space: normal">save/load</code></a> |
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| 38 | <dt><a href="#archives">Archives</a> |
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| 39 | <dt><a href="#examples">List of examples</a> |
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| 40 | </dl> |
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| 41 | An output archive is similar to an output data stream. Data can be saved to the archive |
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| 42 | with either the << or the & operator: |
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| 43 | <pre><code> |
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| 44 | ar << data; |
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| 45 | ar & data; |
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| 46 | </code></pre> |
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| 47 | An input archive is similar to an input datastream. Data can be loaded from the archive |
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| 48 | with either the >> or the & operator. |
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| 49 | <pre><code> |
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| 50 | ar >> data; |
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| 51 | ar & data; |
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| 52 | </code></pre> |
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| 53 | <p> |
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| 54 | When these operators are invoked for primitive data types, the data is simply saved/loaded |
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| 55 | to/from the archive. When invoked for class data types, the class |
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| 56 | <code style="white-space: normal">serialize</code> function is invoked. Each |
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| 57 | <code style="white-space: normal">serialize</code> function is uses the above operators |
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| 58 | to save/load its data members. This process will continue in a recursive manner until |
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| 59 | all the data contained in the class is saved/loaded. |
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| 60 | |
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| 61 | <h3><a name="simplecase">A Very Simple Case</a></h3> |
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| 62 | These operators are used inside the <code style="white-space: normal">serialize</code> |
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| 63 | function to save and load class data members. |
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| 64 | <p> |
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| 65 | Included in this library is a program called |
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| 66 | <a href="../example/demo.cpp" target="demo_cpp">demo.cpp</a> which illustrates how |
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| 67 | to use this system. Below we excerpt code from this program to |
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| 68 | illustrate with the simplest possible case how this library is |
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| 69 | intended to be used. |
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| 70 | <pre> |
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| 71 | <code> |
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| 72 | #include <fstream> |
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| 73 | |
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| 74 | // include headers that implement a archive in simple text format |
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| 75 | #include <boost/archive/text_oarchive.hpp> |
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| 76 | #include <boost/archive/text_iarchive.hpp> |
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| 77 | |
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| 78 | ///////////////////////////////////////////////////////////// |
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| 79 | // gps coordinate |
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| 80 | // |
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| 81 | // illustrates serialization for a simple type |
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| 82 | // |
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| 83 | class gps_position |
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| 84 | { |
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| 85 | private: |
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| 86 | friend class boost::serialization::access; |
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| 87 | // When the class Archive corresponds to an output archive, the |
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| 88 | // & operator is defined similar to <<. Likewise, when the class Archive |
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| 89 | // is a type of input archive the & operator is defined similar to >>. |
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| 90 | template<class Archive> |
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| 91 | void serialize(Archive & ar, const unsigned int version) |
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| 92 | { |
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| 93 | ar & degrees; |
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| 94 | ar & minutes; |
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| 95 | ar & seconds; |
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| 96 | } |
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| 97 | int degrees; |
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| 98 | int minutes; |
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| 99 | float seconds; |
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| 100 | public: |
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| 101 | gps_position(){}; |
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| 102 | gps_position(int d, int m, float s) : |
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| 103 | degrees(d), minutes(m), seconds(s) |
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| 104 | {} |
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| 105 | }; |
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| 106 | |
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| 107 | int main() { |
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| 108 | // create and open a character archive for output |
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| 109 | std::ofstream ofs("filename"); |
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| 110 | |
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| 111 | // create class instance |
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| 112 | const gps_position g(35, 59, 24.567f); |
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| 113 | |
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| 114 | // save data to archive |
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| 115 | { |
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| 116 | boost::archive::text_oarchive oa(ofs); |
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| 117 | // write class instance to archive |
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| 118 | oa << g; |
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| 119 | // archive and stream closed when destructors are called |
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| 120 | } |
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| 121 | |
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| 122 | // ... some time later restore the class instance to its orginal state |
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| 123 | gps_position newg; |
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| 124 | { |
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| 125 | // create and open an archive for input |
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| 126 | std::ifstream ifs("filename", std::ios::binary); |
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| 127 | boost::archive::text_iarchive ia(ifs); |
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| 128 | // read class state from archive |
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| 129 | ia >> newg; |
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| 130 | // archive and stream closed when destructors are called |
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| 131 | } |
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| 132 | return 0; |
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| 133 | } |
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| 134 | </code> |
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| 135 | </pre> |
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| 136 | <p>For each class to be saved via serialization, there must exist a function to |
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| 137 | save all the class members which define the state of the class. |
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| 138 | For each class to be loaded via serialization, there must exist a function to |
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| 139 | load theese class members in the same sequence as they were saved. |
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| 140 | In the above example, these functions are generated by the |
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| 141 | template member function <code style="white-space: normal">serialize</code>. |
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| 142 | |
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| 143 | <h3><a name="nonintrusiveversion">Non Intrusive Version</a></h3> |
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| 144 | <p>The above formulation is intrusive. That is, it requires |
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| 145 | that classes whose instances are to be serialized be |
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| 146 | altered. This can be inconvenient in some cases. |
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| 147 | An equivalent alternative formulation permitted by the |
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| 148 | system would be: |
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| 149 | <pre><code> |
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| 150 | #include <boost/archive/text_oarchive.hpp> |
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| 151 | #include <boost/archive/text_iarchive.hpp> |
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| 152 | |
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| 153 | class gps_position |
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| 154 | { |
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| 155 | public: |
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| 156 | int degrees; |
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| 157 | int minutes; |
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| 158 | float seconds; |
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| 159 | gps_position(){}; |
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| 160 | gps_position(int d, int m, float s) : |
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| 161 | degrees(d), minutes(m), seconds(s) |
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| 162 | {} |
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| 163 | }; |
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| 164 | |
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| 165 | namespace boost { |
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| 166 | namespace serialization { |
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| 167 | |
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| 168 | template<class Archive> |
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| 169 | void serialize(Archive & ar, gps_position & g, const unsigned int version) |
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| 170 | { |
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| 171 | ar & g.degrees; |
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| 172 | ar & g.minutes; |
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| 173 | ar & g.seconds; |
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| 174 | } |
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| 175 | |
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| 176 | } // namespace serialization |
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| 177 | } // namespace boost |
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| 178 | </code></pre> |
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| 179 | <p> |
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| 180 | In this case the generated serialize functions are not members of the |
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| 181 | <code style="white-space: normal">gps_position</code> class. The two formulations function |
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| 182 | in exactly the same way. |
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| 183 | <p> |
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| 184 | The main application of non-intrusive serialization is to permit serialization |
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| 185 | to be implemented for classes without changing the class definition. |
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| 186 | In order for this to be possible, the class must expose enough information |
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| 187 | to reconstruct the class state. In this example, we presumed that the |
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| 188 | class had <code style="white-space: normal">public</code> members - not a common occurence. Only |
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| 189 | classes which expose enough information to save and restore the class |
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| 190 | state will be serializable without changing the class definition. |
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| 191 | <h3><a name="serializablemembers">Serializable Members</a></h3> |
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| 192 | <p> |
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| 193 | A serializable class with serializable members would look like this: |
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| 194 | <pre><code> |
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| 195 | class bus_stop |
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| 196 | { |
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| 197 | friend class boost::serialization::access; |
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| 198 | template<class Archive> |
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| 199 | void serialize(Archive & ar, const unsigned int version) |
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| 200 | { |
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| 201 | ar & latitude; |
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| 202 | ar & longitude; |
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| 203 | } |
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| 204 | gps_position latitude; |
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| 205 | gps_position longitude; |
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| 206 | protected: |
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| 207 | bus_stop(const gps_position & lat_, const gps_position & long_) : |
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| 208 | latitude(lat_), longitude(long_) |
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| 209 | {} |
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| 210 | public: |
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| 211 | bus_stop(){} |
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| 212 | // See item # 14 in Effective C++ by Scott Meyers. |
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| 213 | // re non-virtual destructors in base classes. |
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| 214 | virtual ~bus_stop(){} |
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| 215 | }; |
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| 216 | </code></pre> |
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| 217 | <p>That is, members of class type are serialized just as |
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| 218 | members of primitive types are. |
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| 219 | <p> |
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| 220 | Note that saving an instance of the class <code style="white-space: normal">bus_stop</code> |
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| 221 | with one of the archive operators will invoke the |
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| 222 | <code style="white-space: normal">serialize</code> function which saves |
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| 223 | <code style="white-space: normal">latitude</code> and |
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| 224 | <code style="white-space: normal">longitude</code>. Each of these in turn will be saved by invoking |
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| 225 | <code style="white-space: normal">serialize</code> in the definition of |
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| 226 | <code style="white-space: normal">gps_position</code>. In this manner the whole |
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| 227 | data structure is saved by the application of an archive operator to |
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| 228 | just its root item. |
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| 229 | |
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| 230 | |
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| 231 | <h3><a name="derivedclasses">Derived Classes</a></h3> |
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| 232 | <p>Derived classes should include serializations of their base classes. |
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| 233 | <pre><code> |
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| 234 | #include <boost/serialization/base_object.hpp> |
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| 235 | |
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| 236 | class bus_stop_corner : public bus_stop |
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| 237 | { |
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| 238 | friend class boost::serialization::access; |
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| 239 | template<class Archive> |
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| 240 | void serialize(Archive & ar, const unsigned int version) |
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| 241 | { |
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| 242 | // serialize base class information |
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| 243 | ar & boost::serialization::base_object<bus_stop>(*this); |
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| 244 | ar & street1; |
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| 245 | ar & street2; |
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| 246 | } |
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| 247 | std::string street1; |
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| 248 | std::string street2; |
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| 249 | virtual std::string description() const |
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| 250 | { |
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| 251 | return street1 + " and " + street2; |
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| 252 | } |
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| 253 | public: |
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| 254 | bus_stop_corner(){} |
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| 255 | bus_stop_corner(const gps_position & lat_, const gps_position & long_, |
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| 256 | const std::string & s1_, const std::string & s2_ |
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| 257 | ) : |
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| 258 | bus_stop(lat_, long_), street1(s1_), street2(s2_) |
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| 259 | {} |
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| 260 | }; |
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| 261 | </code> |
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| 262 | </pre> |
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| 263 | <p> |
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| 264 | Note the serialization of the base classes from the derived |
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| 265 | class. Do <b>NOT</b> directly call the base class serialize |
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| 266 | functions. Doing so might seem to work but will bypass the code |
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| 267 | that tracks instances written to storage to eliminate redundancies. |
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| 268 | It will also bypass the writing of class version information into |
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| 269 | the archive. For this reason, it is advisable to always make member |
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| 270 | <code style="white-space: normal">serialize</code> functions private. The declaration |
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| 271 | <code style="white-space: normal">friend boost::serialization::access</code> will grant to the |
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| 272 | serialization library access to private member variables and functions. |
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| 273 | <p> |
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| 274 | <h3><a name="pointers">Pointers</a></h3> |
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| 275 | Suppose we define a bus route as an array of bus stops. Given that |
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| 276 | <ol> |
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| 277 | <li>we might have several types of bus stops (remember bus_stop is |
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| 278 | a base class) |
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| 279 | <li>a given bus_stop might appear in more than one route. |
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| 280 | </ol> |
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| 281 | it's convenient to represent a bus route with an array of pointers |
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| 282 | to <code style="white-space: normal">bus_stop</code>. |
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| 283 | <pre> |
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| 284 | <code> |
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| 285 | class bus_route |
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| 286 | { |
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| 287 | friend class boost::serialization::access; |
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| 288 | bus_stop * stops[10]; |
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| 289 | template<class Archive> |
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| 290 | void serialize(Archive & ar, const unsigned int version) |
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| 291 | { |
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| 292 | int i; |
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| 293 | for(i = 0; i < 10; ++i) |
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| 294 | ar & stops[i]; |
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| 295 | } |
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| 296 | public: |
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| 297 | bus_route(){} |
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| 298 | }; |
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| 299 | </code> |
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| 300 | </pre> |
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| 301 | Each member of the array <code style="white-space: normal">stops</code> will be serialized. |
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| 302 | But remember each member is a pointer - so what can this really |
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| 303 | mean? The whole object of this serialization is to permit |
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| 304 | reconstruction of the original data structures at another place |
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| 305 | and time. In order to accomplish this with a pointer, it is |
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| 306 | not sufficient to save the value of the pointer, rather the |
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| 307 | object it points to must be saved. When the member is later |
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| 308 | loaded, a new object has to be created and a new pointer has |
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| 309 | to be loaded into the class member. |
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| 310 | <p> |
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| 311 | If the same pointer is serialized more than once, only one instance |
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| 312 | is be added to the archive. When read back, no data is read back in. |
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| 313 | The only operation that occurs is for the second pointer is set equal to the first |
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| 314 | <p> |
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| 315 | Note that, in this example, the array consists of polymorphic pointers. |
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| 316 | That is, each array element point to one of several possible |
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| 317 | kinds of bus stops. So when the pointer is saved, some sort of class |
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| 318 | identifier must be saved. When the pointer is loaded, the class |
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| 319 | identifier must be read and and instance of the corresponding class |
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| 320 | must be constructed. Finally the data can be loaded to newly created |
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| 321 | instance of the correct type. |
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| 322 | |
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| 323 | As can be seen in |
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| 324 | <a href="../example/demo.cpp" target="demo_cpp">demo.cpp</a>, |
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| 325 | serialization of pointers to derived classes through a base |
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| 326 | clas pointer may require explicit enumeration of the derived |
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| 327 | classes to be serialized. This is referred to as "registration" or "export" |
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| 328 | of derived classes. This requirement and the methods of |
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| 329 | satisfying it are explained in detail |
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| 330 | <a href="serialization.html#derivedpointers">here</a> |
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| 331 | <p> |
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| 332 | All this is accomplished automatically by the serialization |
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| 333 | library. The above code is all that is necessary to accomplish |
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| 334 | the saving and loading of objects accessed through pointers. |
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| 335 | <p> |
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| 336 | <h3><a name="arrays">Arrays</a></h3> |
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| 337 | The above formulation is in fact more complex than necessary. |
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| 338 | The serialization library detects when the object being |
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| 339 | serialized is an array and emits code equivalent to the above. |
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| 340 | So the above can be shortened to: |
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| 341 | <pre> |
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| 342 | <code> |
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| 343 | class bus_route |
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| 344 | { |
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| 345 | friend class boost::serialization::access; |
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| 346 | bus_stop * stops[10]; |
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| 347 | template<class Archive> |
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| 348 | void serialize(Archive & ar, const unsigned int version) |
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| 349 | { |
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| 350 | ar & stops; |
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| 351 | } |
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| 352 | public: |
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| 353 | bus_route(){} |
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| 354 | }; |
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| 355 | </code> |
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| 356 | </pre> |
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| 357 | <h3><a name="stl">STL Collections</a></h3> |
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| 358 | The above example uses an array of members. More likely such |
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| 359 | an application would use an STL collection for such a purpose. |
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| 360 | The serialization library contains code for serialization |
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| 361 | of all STL classes. Hence, the reformulation below will |
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| 362 | also work as one would expect. |
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| 363 | <pre> |
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| 364 | <code> |
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| 365 | #include <boost/serialization/list.hpp> |
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| 366 | |
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| 367 | class bus_route |
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| 368 | { |
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| 369 | friend class boost::serialization::access; |
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| 370 | std::list<bus_stop *> stops; |
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| 371 | template<class Archive> |
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| 372 | void serialize(Archive & ar, const unsigned int version) |
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| 373 | { |
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| 374 | ar & stops; |
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| 375 | } |
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| 376 | public: |
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| 377 | bus_route(){} |
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| 378 | }; |
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| 379 | </code> |
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| 380 | </pre> |
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| 381 | <h3><a name="versioning">Class Versioning</a></h3> |
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| 382 | <p> |
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| 383 | Suppose we're satisfied with our <code style="white-space: normal">bus_route</code> class, build a program |
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| 384 | that uses it and ship the product. Some time later, it's decided |
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| 385 | that the program needs enhancement and the <code style="white-space: normal">bus_route</code> class is |
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| 386 | altered to include the name of the driver of the route. So the |
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| 387 | new version looks like: |
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| 388 | <pre> |
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| 389 | <code> |
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| 390 | #include <boost/serialization/list.hpp> |
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| 391 | #include <boost/serialization/string.hpp> |
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| 392 | |
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| 393 | class bus_route |
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| 394 | { |
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| 395 | friend class boost::serialization::access; |
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| 396 | std::list<bus_stop *> stops; |
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| 397 | std::string driver_name; |
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| 398 | template<class Archive> |
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| 399 | void serialize(Archive & ar, const unsigned int version) |
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| 400 | { |
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| 401 | ar & driver_name; |
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| 402 | ar & stops; |
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| 403 | } |
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| 404 | public: |
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| 405 | bus_route(){} |
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| 406 | }; |
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| 407 | </code> |
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| 408 | </pre> |
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| 409 | Great, we're all done. Except... what about people using our application |
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| 410 | who now have a bunch of files created under the previous program. |
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| 411 | How can these be used with our new program version? |
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| 412 | <p> |
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| 413 | In general, the serialization library stores a version number in the |
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| 414 | archive for each class serialized. By default this version number is 0. |
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| 415 | When the archive is loaded, the version number under which it was saved |
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| 416 | is read. The above code can be altered to exploit this |
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| 417 | <pre> |
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| 418 | <code> |
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| 419 | #include <boost/serialization/list.hpp> |
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| 420 | #include <boost/serialization/string.hpp> |
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| 421 | #include <boost/serialization/version.hpp> |
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| 422 | |
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| 423 | class bus_route |
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| 424 | { |
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| 425 | friend class boost::serialization::access; |
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| 426 | std::list<bus_stop *> stops; |
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| 427 | std::string driver_name; |
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| 428 | template<class Archive> |
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| 429 | void serialize(Archive & ar, const unsigned int version) |
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| 430 | { |
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| 431 | // only save/load driver_name for newer archives |
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| 432 | if(version > 0) |
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| 433 | ar & driver_name; |
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| 434 | ar & stops; |
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| 435 | } |
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| 436 | public: |
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| 437 | bus_route(){} |
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| 438 | }; |
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| 439 | |
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| 440 | BOOST_CLASS_VERSION(bus_route, 1) |
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| 441 | </code> |
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| 442 | </pre> |
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| 443 | By application of versioning to each class, there is no need to |
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| 444 | try to maintain a versioning of files. That is, a file version |
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| 445 | is the combination of the versions of all its constituent classes. |
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| 446 | |
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| 447 | This system permits programs to be always compatible with archives |
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| 448 | created by all previous versions of a program with no more |
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| 449 | effort than required by this example. |
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| 450 | |
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| 451 | <h3><a name="splitting">Splitting <code style="white-space: normal">serialize</code> |
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| 452 | into <code style="white-space: normal">save/load</code></a></h3> |
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| 453 | The <code style="white-space: normal">serialize</code> function is simple, concise, and guarantees |
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| 454 | that class members are saved and loaded in the same sequence |
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| 455 | - the key to the serialization system. However, there are cases |
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| 456 | where the load and save operations are not as similar as the examples |
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| 457 | used here. For example, this could occur with a class that has evolved through |
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| 458 | multiple versions. The above class can be reformulated as: |
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| 459 | <pre> |
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| 460 | <code> |
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| 461 | #include <boost/serialization/list.hpp> |
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| 462 | #include <boost/serialization/string.hpp> |
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| 463 | #include <boost/serialization/version.hpp> |
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| 464 | #include <boost/serialization/split_member.hpp> |
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| 465 | |
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| 466 | class bus_route |
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| 467 | { |
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| 468 | friend class boost::serialization::access; |
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| 469 | std::list<bus_stop *> stops; |
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| 470 | std::string driver_name; |
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| 471 | template<class Archive> |
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| 472 | void save(Archive & ar, const unsigned int version) const |
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| 473 | { |
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| 474 | // note, version is always the latest when saving |
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| 475 | ar & driver_name; |
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| 476 | ar & stops; |
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| 477 | } |
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| 478 | template<class Archive> |
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| 479 | void load(Archive & ar, const unsigned int version) |
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| 480 | { |
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| 481 | if(version > 0) |
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| 482 | ar & driver_name; |
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| 483 | ar & stops; |
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| 484 | } |
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| 485 | BOOST_SERIALIZATION_SPLIT_MEMBER() |
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| 486 | public: |
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| 487 | bus_route(){} |
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| 488 | }; |
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| 489 | |
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| 490 | BOOST_CLASS_VERSION(bus_route, 1) |
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| 491 | </code> |
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| 492 | </pre> |
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| 493 | The macro <code style="white-space: normal">BOOST_SERIALIZATION_SPLIT_MEMBER()</code> generates |
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| 494 | code which invokes the <code style="white-space: normal">save</code> |
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| 495 | or <code style="white-space: normal">load</code> |
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| 496 | depending on whether the archive is used for saving or loading. |
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| 497 | <h3><a name="archives">Archives</a></h3> |
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| 498 | Our discussion here has focused on adding serialization |
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| 499 | capability to classes. The actual rendering of the data to be serialized |
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| 500 | is implemented in the archive class. Thus the stream of serialized |
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| 501 | data is a product of the serialization of the class and the |
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| 502 | archive selected. It is a key design decision that these two |
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| 503 | components be independent. This permits any serialization specification |
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| 504 | to be usable with any archive. |
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| 505 | <p> |
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| 506 | In this tutorial, we have used a particular |
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| 507 | archive class - <code style="white-space: normal">text_oarchive</code> for saving and |
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| 508 | <code style="white-space: normal">text_iarchive</code> for loading. |
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| 509 | text archives render data as text and are portable across platforms. In addition |
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| 510 | to text archives, the library includes archive class for native binary data |
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| 511 | and xml formatted data. Interfaces to all archive classes are all identical. |
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| 512 | Once serialization has been defined for a class, that class can be serialized to |
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| 513 | any type of archive. |
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| 514 | <p> |
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| 515 | If the current set of archive classes doesn't provide the |
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| 516 | attributes, format, or behavior needed for a particular application, |
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| 517 | one can either make a new archive class or derive from an existing one. |
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| 518 | This is described later in the manual. |
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| 519 | |
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| 520 | <h3><a name="examples">List of Examples</h3> |
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| 521 | <dl> |
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| 522 | <dt><a href="../example/demo.cpp" target="demo_cpp">demo.cpp</a> |
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| 523 | <dd>This is the completed example used in this tutorial. |
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| 524 | It does the following: |
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| 525 | <ol> |
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| 526 | <li>Creates a structure of differing kinds of stops, routes and schedules |
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| 527 | <li>Displays it |
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| 528 | <li>Serializes it to a file named "testfile.txt" with one |
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| 529 | statement |
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| 530 | <li>Restores to another structure |
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| 531 | <li>Displays the restored structure |
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| 532 | </ol> |
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| 533 | <a href="../example/demo_output.txt" target="demo_output">Output of |
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| 534 | this program</a> is sufficient to verify that all the |
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| 535 | originally stated requirements for a serialization system |
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| 536 | are met with this system. The <a href="../example/demofile.txt" |
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| 537 | target="test_file">contents of the archive file</a> can |
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| 538 | also be displayed as serialization files are ASCII text. |
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| 539 | |
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| 540 | <dt><a href="../example/demo_xml.cpp" target="demo_xml_cpp">demo_xml.cpp</a> |
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| 541 | <dd>This is a variation the original demo which supports xml archives in addition |
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| 542 | to the others. The extra wrapping macros are needed to associate a data |
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| 543 | item name with the corresponding xml tag. For more information see |
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| 544 | <a target="detail" href="wrappers.html#nvp">Name-Value Pairs</a>. |
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| 545 | <a href="../example/demo_save.xml" target="demo_save_xml">Here</a> |
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| 546 | is what an xml archive looks like. |
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| 547 | |
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| 548 | <dt><a href="../example/demo_xml_save.cpp" target="demo_xml_save_cpp">demo_xml_save.cpp</a> |
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| 549 | and <a href="../example/demo_xml_load.cpp" target="demo_xml_load_cpp">demo_xml_load.cpp</a> |
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| 550 | <dd>Note also that though our examples save and load the program data |
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| 551 | to an archive within the same program, this merely a convenience |
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| 552 | for purposes of illustration. In general, the archive may or may |
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| 553 | not be loaded by the same program that created it. |
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| 554 | </dl> |
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| 555 | <p> |
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| 556 | The astute reader might notice that these examples contain a subtle but important flaw. |
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| 557 | They leak memory. The bus stops are created in the <code style="white-space: normal"> |
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| 558 | main</code> function. The bus schedules may refer to these bus stops |
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| 559 | any number of times. At the end of the main function after the bus schedules are destroyed, |
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| 560 | the bus stops are destroyed. This seems fine. But what about the structure |
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| 561 | <code style="white-space: normal">new_schedule</code> data item created by the |
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| 562 | process of loading from an archive? This contains its own separate set of bus stops |
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| 563 | that are not referenced outside of the bus schedule. These won't be destroyed |
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| 564 | anywhere in the program - a memory leak. |
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| 565 | <p> |
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| 566 | There are couple of ways of fixing this. One way is to explicitly manage the bus stops. |
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| 567 | However, a more robust and transparent is to use |
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| 568 | <code style="white-space: normal">shared_ptr</code> rather than raw pointers. Along |
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| 569 | with serialization implemenations for the Standard Library, the serialization library |
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| 570 | includes implementation of serialization for |
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| 571 | <code style="white-space: normal">boost::shared ptr</code>. Given this, it should be |
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| 572 | easy to alter any of these examples to eliminate the memory leak. This is left |
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| 573 | as an excercise for the reader. |
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| 574 | |
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| 575 | <hr> |
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| 576 | <p><i>© Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 2002-2004. |
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| 577 | Distributed under the Boost Software License, Version 1.0. (See |
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| 578 | accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
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| 579 | </i></p> |
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| 580 | </body> |
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| 581 | </html> |
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