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| 3 | <!-- |
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| 4 | (C) Copyright 2002-4 Robert Ramey - http://www.rrsd.com . |
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| 5 | Use, modification and distribution is subject to the Boost Software |
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| 6 | License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
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| 7 | http://www.boost.org/LICENSE_1_0.txt) |
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| 8 | --> |
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| 9 | <head> |
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| 10 | <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> |
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| 11 | <link rel="stylesheet" type="text/css" href="../../../boost.css"> |
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| 12 | <link rel="stylesheet" type="text/css" href="style.css"> |
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| 13 | <title>Serialization - BOOST_STATIC_WARNING</title> |
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| 14 | </head> |
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| 15 | <body link="#0000ff" vlink="#800080"> |
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| 16 | <table border="0" cellpadding="7" cellspacing="0" width="100%" summary="header"> |
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| 17 | <tr> |
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| 18 | <td valign="top" width="300"> |
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| 19 | <h3><a href="../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../boost.png" border="0"></a></h3> |
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| 20 | </td> |
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| 21 | <td valign="top"> |
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| 22 | <h1 align="center">Serialization</h1> |
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| 23 | <h2 align="center"><code>void_cast</code></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 | <h3>Motivation</h3> |
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| 29 | C++ includes the operator <code style="white-space: normal">dynamic_cast<T>(U * u)</code> |
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| 30 | for casting a pointer at runtime between two related types. However, this can only be |
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| 31 | used for polymorphic classes. That is, it can only be used with related classes which have at least one virtual function. |
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| 32 | Limiting the serializaton of pointers to only such class would diminish the applicability |
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| 33 | of the library. |
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| 34 | |
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| 35 | <h3>Usage</h3> |
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| 36 | |
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| 37 | The following functions are defined in the header |
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| 38 | <a target="void_cast" href="../../../boost/serialization/void_cast.hpp">void_cast.hpp</a>. |
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| 39 | They are declared in the namespace |
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| 40 | <code style="white-space: normal">boost::serialization</code>. |
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| 41 | |
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| 42 | <dl> |
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| 43 | <dt><h4><pre><code> |
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| 44 | template<class Derived, class Base> |
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| 45 | const void_cast_detail::void_caster & |
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| 46 | void_cast_register( |
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| 47 | const Derived * derived = NULL, |
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| 48 | const Base * base = NULL |
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| 49 | ) |
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| 50 | </code></pre></h4></dt> |
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| 51 | <dd> |
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| 52 | This function "registers" a pair of related types. It stores the fact that |
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| 53 | <code style="white-space: normal">Derived</code> is immediately derived from |
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| 54 | <code style="white-space: normal">Base</code> in a global table. |
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| 55 | <ul> |
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| 56 | <li>This "registration" can be invoked anywhere in the program. The table is built at |
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| 57 | pre-runtime and is available anywhere else in the program. |
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| 58 | <li>only adjacent base/derived pairs need be registered. That is, |
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| 59 | <pre><code> |
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| 60 | void_cast_register<A, B>(); |
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| 61 | void_cast_register<B, C>(); |
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| 62 | </code></pre> |
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| 63 | automatically derives the fact that A can be upcast to C and vice-versa. |
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| 64 | </ul> |
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| 65 | </dd> |
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| 66 | |
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| 67 | <dt><h4><pre><code> |
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| 68 | void * |
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| 69 | void_upcast( |
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| 70 | extended_type_info const & derived_type, |
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| 71 | extended_type_info const & base_type, |
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| 72 | void * const t |
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| 73 | ); |
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| 74 | </code></pre></h4></dt> |
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| 75 | |
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| 76 | <dt><h4><pre><code> |
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| 77 | void * |
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| 78 | void_downcast( |
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| 79 | extended_type_info const & derived_type, |
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| 80 | extended_type_info const & base_type, |
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| 81 | void * const t |
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| 82 | ); |
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| 83 | </code></pre></h4></dt> |
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| 84 | <dd> |
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| 85 | These functions cast a void pointer from one type to another. The source and |
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| 86 | definition types are specified by passing references to the corresponding |
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| 87 | <a href="extended_type_info.html"><code style="white-space: normal"> |
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| 88 | extended_type_info</code></a> |
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| 89 | records. An attempt to cast between types not "registered" with |
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| 90 | <code style="white-space: normal">void_cast_register</code> |
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| 91 | will throw a |
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| 92 | <a href="exceptions.html"><code style="white-space: normal">boost::archive::archive_exception</code></a> |
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| 93 | with value equal to |
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| 94 | <code style="white-space: normal">unregistered_cast</code> |
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| 95 | </dd> |
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| 96 | </dl> |
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| 97 | |
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| 98 | <hr> |
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| 99 | <p><i>© Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 2002-2004. |
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| 100 | Distributed under the Boost Software License, Version 1.0. (See |
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| 101 | accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
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| 102 | </i></p> |
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| 103 | </body> |
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| 104 | </html> |
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