ceph/src/boost/libs/serialization/doc/void_cast.html

   1 <!doctype HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
   2 <html>
   3 <!--
   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&lt;T&gt;(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&lt;class Derived, class Base&gt;
  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&lt;A, B&gt;();
  61   void_cast_register&lt;B, C&gt;();
  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>&copy; 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>