| 1 | <!doctype HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
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| 2 | <html> |
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| 3 | <head> |
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| 4 | <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> |
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| 5 | <link rel="stylesheet" type="text/css" href="../../../boost.css"> |
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| 6 | <link rel="stylesheet" type="text/css" href="style.css"> |
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| 7 | <title>Serialization - Archives</title> |
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| 8 | </head> |
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| 9 | <body link="#0000ff" vlink="#800080"> |
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| 10 | <table border="0" cellpadding="7" cellspacing="0" width="100%" summary="header"> |
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| 11 | <tr> |
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| 12 | <td valign="top" width="300"> |
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| 13 | <h3><a href="../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../boost.png" border="0"></a></h3> |
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| 14 | </td> |
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| 15 | <td valign="top"> |
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| 16 | <h1 align="center">Serialization</h1> |
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| 17 | <h2 align="center">Archive Concepts</h2> |
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| 18 | </td> |
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| 19 | </tr> |
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| 20 | </table> |
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| 21 | <hr> |
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| 22 | <dl class="page-index"> |
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| 23 | <dt><a href="#saving_interface">Saving Archive Concept</a> |
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| 24 | <dt><a href="#loading_interface">Loading Archive Concept</a> |
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| 25 | <dt><a href="#archive_models">Models</a> |
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| 26 | <dt><a href="#exceptions">Exceptions</a> |
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| 27 | <dt><a href="#charactersets">Character Sets</a> |
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| 28 | </dl> |
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| 29 | <h4>Notation</h4> |
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| 30 | In the following descriptions |
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| 31 | <ul> |
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| 32 | <li><code>SA</code> is an type modeling the <a href="#saving_interface">Saving Archive Concept</a> |
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| 33 | <li><code>sa</code> is an instance of type SA. |
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| 34 | <li><code>LA</code> is an type modeling the <a href="#loading_interface">Loading Archive Concept</a> |
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| 35 | <li><code>la</code> is an instance of type LA. |
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| 36 | <li><code>T</code> is an <a href="serialization.html"><strong>Serializable</strong></a> Type |
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| 37 | <li><code>x</code> is an instance of type T Type</li>. |
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| 38 | <li><code>u,v</code> is a pointer to a an instance of type T |
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| 39 | <li><code>count</code> is an instance of a type that can be converted to <code>std::size_t</code>. |
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| 40 | </ul> |
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| 41 | <h4><a name="saving_interface">Saving Archive Concept</a></h4> |
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| 42 | <h4>Associated Types</h4> |
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| 43 | Intuitively, a type modeling this concept will generate a sequence of bytes |
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| 44 | correpsonding to an arbitrary set of C++ data structures. Each type modeling the |
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| 45 | Saving Archive concept (SA) may be associated with another type modeling the |
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| 46 | <a href="#loading_interface">Loading Archive Concept</a>(LA). |
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| 47 | This associated type will perform the inverse operation. |
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| 48 | That is, given a sequence of bytes generated by SA, it will generate a set of |
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| 49 | C++ data structures the is equivalent to the original. |
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| 50 | The notion of equivalence is defined by the implementations of the pair of archives and the |
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| 51 | way the data is are rendered <a href="serialization.html">serializable</a>. |
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| 52 | <p> |
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| 53 | <h4>Valid Expressions</h4> |
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| 54 | <dl> |
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| 55 | <dt><h4><code> |
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| 56 | SA::is_saving |
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| 57 | </code></h4></dt> |
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| 58 | <dd> |
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| 59 | Returns the Boost MPL Integral Constant type boost::mpl::bool_<true> |
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| 60 | </dd> |
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| 61 | <dt><h4><code> |
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| 62 | SA::is_loading |
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| 63 | </code></h4></dt> |
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| 64 | <dd> |
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| 65 | Returns the Boost MPL Integral Constant type boost::mpl::bool_<false> |
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| 66 | </dd> |
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| 67 | <dt><h4><code> |
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| 68 | sa << x |
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| 69 | <br> |
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| 70 | sa & x |
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| 71 | </code></h4></dt> |
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| 72 | <dd> |
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| 73 | These expressions must perform exactly the same function. They append the |
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| 74 | value of <code style="white-space: normal">x</code> along with other information to <code>sa</code>. |
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| 75 | This other information is defined by the implementation of the archive. |
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| 76 | Typically this information is that which is required by a corresponding |
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| 77 | Loading Archive type to properly restore the value of <code>x</code>. |
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| 78 | <p> |
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| 79 | Returns a reference to <code>sa</code>. |
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| 80 | </dd> |
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| 81 | <dt><h4><code> |
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| 82 | sa.save_binary(u, count) |
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| 83 | </code></h4></dt> |
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| 84 | <dd> |
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| 85 | Appends to the archive <code style="white-space: normal">size_t(count)</code> bytes found at |
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| 86 | <code style="white-space: normal">u</code>. |
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| 87 | </dd> |
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| 88 | <dt><h4><code> |
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| 89 | sa.register_type<T>() |
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| 90 | <br> |
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| 91 | sa.register_type(u) |
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| 92 | </code></h4></dt> |
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| 93 | <dd> |
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| 94 | Appends information about class T to the archive. This information is used to |
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| 95 | construct the correct class when a derived pointer is loaded by a corresponding |
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| 96 | Loading Archive type. |
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| 97 | Invocation of this member function is referred to as "class registration". |
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| 98 | This is explained in detail in |
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| 99 | <a href="special.html#derivedpointers">Special Considerations - Derived Pointers</a>. |
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| 100 | The second syntax is included to permit this function to be called on non-conforming |
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| 101 | compilers when <code style="white-space: normal">sa</code> is a template argument. |
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| 102 | For more information, see <a target="detail" href="implementation.html#tempatesyntax">Template Invocation syntax</a> |
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| 103 | </dd> |
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| 104 | <dt><h4><code> |
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| 105 | sa.library_version() |
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| 106 | </code></h4></dt> |
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| 107 | <dd> |
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| 108 | Returns an unsigned integer containing the current version number of the serialization |
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| 109 | library. This number will be incremented each time the library is altered in such a |
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| 110 | way that serialization could be altered for some type. For example, suppose the type |
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| 111 | used for a count of collection members is changed. The code that loads collections |
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| 112 | might be conditioned on the library version to make sure that libraries created by |
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| 113 | previous versions of the library can still be read. |
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| 114 | </dd> |
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| 115 | </dl> |
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| 116 | |
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| 117 | <h4><a name="loading_interface">Loading Archive Concept</a></h4> |
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| 118 | <h4>Associated Types</h4> |
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| 119 | Each model of this concept presumes the |
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| 120 | existence of a corresponding type modeling the |
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| 121 | <a href="#saving_interface">Saving Archive Concept</a>. |
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| 122 | The purpose of an instance of this concept is to convert a sequence of bytes |
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| 123 | generated by this corresponding type to a set of C++ data structures |
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| 124 | equivalent to the original. |
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| 125 | <h4>Valid Expressions</h4> |
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| 126 | <dl> |
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| 127 | <dt><h4><code> |
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| 128 | LA::is_saving |
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| 129 | </code></h4></dt> |
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| 130 | <dd> |
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| 131 | Returns the Boost MPL Integral Constant type boost::mpl::bool_<false> |
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| 132 | </dd> |
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| 133 | <dt><h4><code> |
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| 134 | LA::is_loading |
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| 135 | </code></h4></dt> |
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| 136 | <dd> |
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| 137 | Returns the Boost MPL Integral Constant type boost::mpl::bool_<true> |
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| 138 | </dd> |
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| 139 | <dt><h4><code> |
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| 140 | la >> x |
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| 141 | <br> |
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| 142 | la & x |
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| 143 | </code></h4></dt> |
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| 144 | <dd> |
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| 145 | These expressions must perform exactly the same function. |
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| 146 | Sets <code>x</code> to a value retrieved from <code>la</code>. |
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| 147 | <p> |
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| 148 | Returns a reference to <code>la</code>. |
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| 149 | </dd> |
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| 150 | <dt><h4><code> |
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| 151 | la.load_binary(u, count) |
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| 152 | </code></h4></dt> |
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| 153 | <dd> |
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| 154 | Retrieves from <code style="white-space: normal">la</code> <code style="white-space: normal">size_t(count)</code> bytes and stores |
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| 155 | them in memory starting at <code style="white-space: normal">u</code>. |
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| 156 | </dd> |
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| 157 | <dt> |
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| 158 | <dt><h4><code> |
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| 159 | la.register_type<T>() |
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| 160 | <br> |
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| 161 | la.register_type(u) |
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| 162 | </code></h4></dt> |
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| 163 | <dd> |
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| 164 | Retrieves information about class T from the archive. This information is used to |
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| 165 | construct the correct class when loading a pointer to a derived class not |
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| 166 | otherwise referred to in the program by name. |
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| 167 | Invocation of this member function is referred to as "class registration". |
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| 168 | This is explained in detail in |
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| 169 | <a href="special.html#derivedpointers">Special Considerations - Derived Pointers</a>. |
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| 170 | The second syntax is included to permit this function to be called on non-conforming |
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| 171 | compilers when <code style="white-space: normal">la</code> is a template argument. |
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| 172 | For more information, see <a target="detail" href="implementation.html#tempatesyntax">Template Invocation syntax</a> |
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| 173 | </dd> |
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| 174 | <dt><h4><code> |
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| 175 | la.library_version() |
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| 176 | </code></h4></dt> |
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| 177 | <dd> |
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| 178 | Returns an unsigned integer containing the version number of the serialization |
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| 179 | library that created the archive. This number will be incremented each time the |
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| 180 | library is altered in such a way that serialization could be altered for some type. |
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| 181 | For example, suppose the type used for a count of collection members is changed. |
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| 182 | The code that loads collections might be conditioned on the library version to make |
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| 183 | sure that libraries created by previous versions of the library can still be read. |
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| 184 | </dd> |
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| 185 | <dt><h4><code> |
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| 186 | la.reset_object_address(v, u) |
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| 187 | </code></h4></dt> |
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| 188 | <dd> |
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| 189 | Communicates to the archive that the object originally at address u has been |
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| 190 | moved to address v. |
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| 191 | <p> |
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| 192 | When an object is loaded to a temporary variable and later moved to another location, |
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| 193 | This function must be called in order communicate this fact. This is permits the |
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| 194 | the archive to properly implement object tracking. Object tracking is required in order |
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| 195 | to correctly implement serialization of pointers to instances of derived classes. |
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| 196 | </dd> |
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| 197 | <dt><h4><code> |
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| 198 | la.delete_created_pointers() |
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| 199 | </code></h4></dt> |
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| 200 | <dd> |
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| 201 | Deletes all objects created by the loading of pointers. This can be used to |
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| 202 | avoid memory leaks that might otherwise occur if pointers are being loaded |
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| 203 | and the archive load encounters an exception. |
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| 204 | </dd> |
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| 205 | </dl> |
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| 206 | |
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| 207 | There are archives based on text, binary and XML file |
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| 208 | formats but all have the above interface. Given that all archives present |
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| 209 | the same public interface, specifcation of serialization is exactly the same |
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| 210 | for all archives. Archive classes have other members not mentioned here. |
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| 211 | However they are related to the internal functioning of the library and |
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| 212 | are not meant to be called by users of an archive. Implementation of new |
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| 213 | archives is discussed in |
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| 214 | <a href="archive_reference.html#implementation">New Archives - Implementation</a>. |
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| 215 | |
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| 216 | <p> |
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| 217 | The existence of the <code style="white-space: normal"><<</code> |
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| 218 | and <code style="white-space: normal">>></code> suggest |
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| 219 | a relationship between archives and C++ i/o streams. <strong>Archives are not |
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| 220 | C++ i/o streams</strong>. All the archives included with this system take a stream |
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| 221 | as an argument in the constructor and that stream is used for output or input. |
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| 222 | However, this is not a requirement of the serialization functions or the |
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| 223 | archive interface. It just turns out that the archives written so far have |
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| 224 | found it useful to base their implementation on streams. |
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| 225 | |
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| 226 | <h3><a name="archive_models">Archive Models</a></h3> |
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| 227 | This library includes a various implementation of the Archive concept. |
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| 228 | |
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| 229 | An archive is defined by two complementary classes. One is for saving data while |
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| 230 | the other is for loading it. |
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| 231 | |
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| 232 | This library includes a number of archive implementations that are "ready to go" for the |
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| 233 | most common requirements. These classes implement the archive concept for differing data formats. |
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| 234 | They can be used "as is" or as a basis for developing one's own particular type of archive. |
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| 235 | An archive is defined by two complementary classes. One is for saving data while the other is for loading it. |
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| 236 | |
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| 237 | To invoke serialization using one of |
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| 238 | these archives, one or more of the following header files must be |
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| 239 | included in the code module containing the serialization code. |
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| 240 | <pre><code> |
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| 241 | // a portable text archive</a> |
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| 242 | <a href="../../../boost/archive/text_oarchive.hpp" target="text_oarchive_cpp">boost::archive::text_oarchive</a> // saving |
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| 243 | <a href="../../../boost/archive/text_iarchive.hpp" target="text_iarchive_cpp">boost::archive::text_iarchive</a> // loading |
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| 244 | |
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| 245 | // a portable text archive using a wide character stream</a> |
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| 246 | <a href="../../../boost/archive/text_woarchive.hpp">boost::archive::text_woarchive</a> // saving |
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| 247 | <a href="../../../boost/archive/text_wiarchive.hpp">boost::archive::text_wiarchive</a> // loading |
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| 248 | |
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| 249 | // a portable XML archive</a> |
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| 250 | <a href="../../../boost/archive/xml_oarchive.hpp" target="xml_oarchive_cpp">boost::archive::xml_oarchive</a> // saving |
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| 251 | <a href="../../../boost/archive/xml_iarchive.hpp" target="xml_iarchive_cpp">boost::archive::xml_iarchive</a> // loading |
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| 252 | |
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| 253 | // a portable XML archive which uses wide characters - use for utf-8 output</a> |
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| 254 | <a href="../../../boost/archive/xml_woarchive.hpp" target="xml_woarchive_cpp">boost::archive::xml_woarchive</a> // saving |
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| 255 | <a href="../../../boost/archive/xml_wiarchive.hpp" target="xml_wiarchive_cpp">boost::archive::xml_wiarchive</a> // loading |
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| 256 | |
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| 257 | // a non-portable native binary archive</a> |
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| 258 | <a href="../../../boost/archive/binary_oarchive.hpp" target="binary_oarchive_cpp">boost::archive::binary_oarchive</a> // saving |
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| 259 | <a href="../../../boost/archive/binary_iarchive.hpp" target="binary_iarchive_cpp">boost::archive::binary_iarchive</a> // loading |
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| 260 | |
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| 261 | <!-- |
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| 262 | // a non-portable native binary archive which use wide character streams |
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| 263 | <a href="../../../boost/archive/binary_woarchive.hpp">boost::archive::binary_woarchive</a> // saving |
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| 264 | <a href="../../../boost/archive/binary_wiarchive.hpp">boost::archive::binary_wiarchive</a> // loading |
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| 265 | --> |
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| 266 | |
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| 267 | </code></pre> |
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| 268 | |
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| 269 | All of these archives implement the same inteface. Hence, it should suffice to describe only one |
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| 270 | of them in detail. For this purpose we will use the text archive. |
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| 271 | |
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| 272 | |
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| 273 | <pre><code> |
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| 274 | namespace boost { |
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| 275 | namespace archive { |
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| 276 | |
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| 277 | enum archive_flags { |
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| 278 | no_header = 1, // suppress archive header info |
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| 279 | no_codecvt = 2, // suppress alteration of codecvt facet |
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| 280 | no_xml_tag_checking = 4 // suppress checking of xml tags - igored on saving |
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| 281 | }; |
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| 282 | |
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| 283 | } // archive |
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| 284 | } // boost |
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| 285 | </code></pre> |
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| 286 | |
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| 287 | <pre><code> |
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| 288 | namespace boost { |
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| 289 | namespace archive { |
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| 290 | |
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| 291 | class text_oarchive : ... |
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| 292 | { |
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| 293 | ... |
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| 294 | public: |
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| 295 | ... // implementation of the <strong>Saving Archive</strong> concept |
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| 296 | text_oarchive(std::ostream & os, unsigned int flags = 0); |
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| 297 | ~text_oarchive(); |
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| 298 | }; |
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| 299 | |
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| 300 | } // archive |
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| 301 | } // boost |
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| 302 | </code></pre> |
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| 303 | |
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| 304 | <dl> |
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| 305 | |
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| 306 | <dt><h4><code> |
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| 307 | text_oarchive(std::ostream & os, unsigned int flags = 0); |
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| 308 | </code></h4></dt> |
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| 309 | <dd> |
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| 310 | Contructs an archive given an open <code style="white-space: normal">stream</code> as |
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| 311 | an argument and optional flags. For most applications there will be no need to use flags. |
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| 312 | Flags are defined by <code style="white-space: normal">enum archive_flags</code> enumerator. |
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| 313 | Multiple flags can be combined with the <code style="white-space: normal">|</code> operator. |
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| 314 | |
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| 315 | By default, archives prepend |
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| 316 | output with initial data which helps identify them as archives produced by this system. |
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| 317 | This permits a more graceful handling of the case where an attempt is made to load an archive |
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| 318 | from an invalid file format. In addition to this, each type of archive might have |
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| 319 | its own information. For example, native binary archives include information about |
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| 320 | sizes of native types and endianess to gracefully handle the case where it has been |
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| 321 | erroneously assumed that such an archive is portable across platforms. In some cases, |
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| 322 | where this extra overhead might be considered objectionable, it can be suppressed with the |
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| 323 | <code style="white-space: normal">no_header</code> flag. |
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| 324 | <p> |
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| 325 | In some cases, an archive may alter (and later restore) |
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| 326 | the codecvt facet of the stream locale. To suppress this action, |
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| 327 | include the <code style="white-space: normal">no_codecvt</code> flag. |
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| 328 | <p> |
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| 329 | XML archives contain nested tags signifying the start and end of data fields. |
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| 330 | These tags are normally checked for agreement with the object name when |
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| 331 | data is loaded. If a mismatch occurs an exception is thrown. It's possible |
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| 332 | that this may not be desired behavior. To suppress this checking of XML |
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| 333 | tags, use <code style="white-space: normal">no_xml_tag_checking</code> flag. |
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| 334 | </dd> |
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| 335 | |
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| 336 | <dt><h4><code> |
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| 337 | ~text_oarchive(); |
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| 338 | </code></h4></dt> |
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| 339 | <dd> |
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| 340 | Destructor for an archive. This should be called before the stream is |
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| 341 | closed. It restores any altered stream facets to their state before the |
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| 342 | the archive was opened. |
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| 343 | </dd> |
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| 344 | |
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| 345 | </dl> |
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| 346 | |
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| 347 | <pre><code> |
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| 348 | namespace boost { |
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| 349 | namespace archive { |
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| 350 | |
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| 351 | class text_iarchive : ... |
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| 352 | { |
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| 353 | ... |
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| 354 | public: |
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| 355 | ... // implementation of the <strong>Loading Archive</strong> concept |
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| 356 | text_iarchive(std::istream & is, unsigned int flags = 0); |
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| 357 | ~text_iarchive(); |
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| 358 | }; |
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| 359 | |
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| 360 | } //namespace archive |
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| 361 | ) //namespace boost |
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| 362 | |
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| 363 | </code></pre> |
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| 364 | |
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| 365 | <dl> |
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| 366 | |
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| 367 | <dt><h4><code> |
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| 368 | text_iarchive(std::istream & is, unsigned int flags = 0); |
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| 369 | </code></h4></dt> |
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| 370 | <dd> |
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| 371 | Contructs an archive given an open <code style="white-space: normal">stream</code> as |
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| 372 | an argument and optional flags. If flags are used, they should be the same |
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| 373 | as those used when the archive was created. Function and usage of flags is described |
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| 374 | above. |
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| 375 | </dd> |
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| 376 | |
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| 377 | <dt><h4><code> |
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| 378 | ~text_iarchive(); |
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| 379 | </code></h4></dt> |
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| 380 | <dd> |
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| 381 | Destructor for an archive. This should be called before the stream is |
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| 382 | closed. It restores any altered stream facets to thier state before the |
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| 383 | the archive was opened. |
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| 384 | </dd> |
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| 385 | </dl> |
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| 386 | <p> |
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| 387 | The <code style="white-space: normal">binary_oarchive</code> and |
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| 388 | <code style="white-space: normal">binary_iarchive</code> classes are |
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| 389 | implemented in terms of the more basic |
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| 390 | <code style="white-space: normal">std::streambuf</code>. So, in addition |
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| 391 | to the common class interface described above, they include the following |
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| 392 | constructors: |
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| 393 | <dl> |
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| 394 | <dt><h4><code> |
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| 395 | binary_oarchive(std::streambuf & bsb, unsigned int flags = 0); |
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| 396 | </code></h4></dt> |
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| 397 | and |
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| 398 | <dt><h4><code> |
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| 399 | binary_iarchive(std::streambuf & bsb, unsigned int flags = 0); |
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| 400 | </code></h4></dt> |
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| 401 | </dl> |
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| 402 | |
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| 403 | <h3><a name="exceptions">Exceptions</h3> |
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| 404 | All of the archive classes included may throw exceptions. The list of exceptions that might |
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| 405 | be throw can be found in section <a target="detail" href="exceptions.html">Archive Exceptions</a> |
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| 406 | of this documentation. |
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| 407 | |
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| 408 | <h3><a name="charactersets">Character Sets</h3> |
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| 409 | This library includes two archive classes for XML. The wide character |
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| 410 | version (<code style="white-space: normal">xml_w?archive</code>) renders it output as UTF-8 which can |
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| 411 | handle any wide character without loss of information. |
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| 412 | <code style="white-space: normal">std::string</code> data is converted from multi-byte format to wide |
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| 413 | character format using the current <code style="white-space: normal"> |
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| 414 | locale</code>. Hence this version should give a fair rendering of all |
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| 415 | C++ data for all cases. This could result in some unexpected behavior. |
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| 416 | Suppose an <code style="white-space: normal">std::string</code> |
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| 417 | is created with the <code style="white-space: normal">locale</code> character |
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| 418 | set to hebrew characters. On output this is converted to wide characters. |
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| 419 | On input however, there could be a problem if the <code style="white-space: normal">locale</code> is |
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| 420 | not set the same as when the archive is created. |
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| 421 | <p> |
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| 422 | The normal character version (<code style="white-space: normal">xml_?archive</code>) renders |
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| 423 | <code style="white-space: normal">std::string</code> output without any conversion. Though this may work |
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| 424 | fine for serialization, it may create difficulties if the XML archive is used |
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| 425 | for some other purpose. |
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| 426 | <hr> |
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| 427 | <p><i>© Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 2002-2004. |
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| 428 | Distributed under the Boost Software License, Version 1.0. (See |
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| 429 | accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
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| 430 | </i></p> |
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| 431 | </body> |
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| 432 | </html> |
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