| Brian Silverman | 8867871 | 2018-08-04 23:56:48 -0700 | [diff] [blame^] | 1 | <!doctype HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
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| 4 | (C) Copyright 2002-4 Robert Ramey - http://www.rrsd.com . |
| 5 | Use, modification and distribution is subject to the Boost Software |
| 6 | License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
| 7 | http://www.boost.org/LICENSE_1_0.txt) |
| 8 | --> |
| 9 | <head> |
| 10 | <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> |
| 11 | <link rel="stylesheet" type="text/css" href="../../../boost.css"> |
| 12 | <link rel="stylesheet" type="text/css" href="style.css"> |
| 13 | <title>Serialization - BOOST_STATIC_WARNING</title> |
| 14 | </head> |
| 15 | <body link="#0000ff" vlink="#800080"> |
| 16 | <table border="0" cellpadding="7" cellspacing="0" width="100%" summary="header"> |
| 17 | <tr> |
| 18 | <td valign="top" width="300"> |
| 19 | <h3><a href="../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../boost.png" border="0"></a></h3> |
| 20 | </td> |
| 21 | <td valign="top"> |
| 22 | <h1 align="center">Serialization</h1> |
| 23 | <h2 align="center"><code>void_cast</code></h2> |
| 24 | </td> |
| 25 | </tr> |
| 26 | </table> |
| 27 | <hr> |
| 28 | <h3>Motivation</h3> |
| 29 | C++ includes the operator <code style="white-space: normal">dynamic_cast<T>(U * u)</code> |
| 30 | for casting a pointer at runtime between two related types. However, this can only be |
| 31 | used for polymorphic classes. That is, it can only be used with related classes which have at least one virtual function. |
| 32 | Limiting the serializaton of pointers to only such classes would diminish the applicability |
| 33 | of the library. |
| 34 | |
| 35 | <h3>Usage</h3> |
| 36 | |
| 37 | The following functions are defined in the header |
| 38 | <a target="void_cast" href="../../../boost/serialization/void_cast.hpp">void_cast.hpp</a>. |
| 39 | They are declared in the namespace |
| 40 | <code style="white-space: normal">boost::serialization</code>. |
| 41 | |
| 42 | <dl> |
| 43 | <dt><h4><pre><code> |
| 44 | template<class Derived, class Base> |
| 45 | const void_cast_detail::void_caster & |
| 46 | void_cast_register( |
| 47 | Derived const * derived = NULL, |
| 48 | Base * const base = NULL |
| 49 | ); |
| 50 | </code></pre></h4></dt> |
| 51 | <dd> |
| 52 | This function "registers" a pair of related types. It stores the fact that |
| 53 | <code style="white-space: normal">Derived</code> is immediately derived from |
| 54 | <code style="white-space: normal">Base</code> in a global table. |
| 55 | <ul> |
| 56 | <li>This "registration" can be invoked anywhere in the program. The table is built at |
| 57 | pre-runtime and is available anywhere else in the program. |
| 58 | <li>only adjacent base/derived pairs need be registered. That is, |
| 59 | <pre><code> |
| 60 | void_cast_register<A, B>(); |
| 61 | void_cast_register<B, C>(); |
| 62 | </code></pre> |
| 63 | automatically derives the fact that A can be upcast to C and vice-versa. |
| 64 | </ul> |
| 65 | </dd> |
| 66 | |
| 67 | <dt><h4><pre><code> |
| 68 | void * |
| 69 | void_upcast( |
| 70 | extended_type_info const & derived_type, |
| 71 | extended_type_info const & base_type, |
| 72 | void * const t |
| 73 | ); |
| 74 | </code></pre></h4></dt> |
| 75 | |
| 76 | <dt><h4><pre><code> |
| 77 | void * |
| 78 | void_downcast( |
| 79 | extended_type_info const & derived_type, |
| 80 | extended_type_info const & base_type, |
| 81 | void * const t |
| 82 | ); |
| 83 | </code></pre></h4></dt> |
| 84 | <dd> |
| 85 | These functions cast a void pointer from one type to another. The source and |
| 86 | definition types are specified by passing references to the corresponding |
| 87 | <a href="extended_type_info.html"><code style="white-space: normal"> |
| 88 | extended_type_info</code></a> |
| 89 | records. An attempt to cast between types not "registered" with |
| 90 | <code style="white-space: normal">void_cast_register</code> |
| 91 | will throw a |
| 92 | <a href="exceptions.html"><code style="white-space: normal">boost::archive::archive_exception</code></a> |
| 93 | with value equal to |
| 94 | <code style="white-space: normal">unregistered_cast</code> |
| 95 | </dd> |
| 96 | </dl> |
| 97 | |
| 98 | <hr> |
| 99 | <p><i>© Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 2002-2004. |
| 100 | Distributed under the Boost Software License, Version 1.0. (See |
| 101 | accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
| 102 | </i></p> |
| 103 | </body> |
| 104 | </html> |