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| <title>Serialization - BOOST_STATIC_WARNING</title> |
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| <h3><a href="../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../boost.png" border="0"></a></h3> |
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| <td valign="top"> |
| <h1 align="center">Serialization</h1> |
| <h2 align="center"><code>void_cast</code></h2> |
| </td> |
| </tr> |
| </table> |
| <hr> |
| <h3>Motivation</h3> |
| C++ includes the operator <code style="white-space: normal">dynamic_cast<T>(U * u)</code> |
| for casting a pointer at runtime between two related types. However, this can only be |
| used for polymorphic classes. That is, it can only be used with related classes which have at least one virtual function. |
| Limiting the serializaton of pointers to only such class would diminish the applicability |
| of the library. |
| |
| <h3>Usage</h3> |
| |
| The following functions are defined in the header |
| <a target="void_cast" href="../../../boost/serialization/void_cast.hpp">void_cast.hpp</a>. |
| They are declared in the namespace |
| <code style="white-space: normal">boost::serialization</code>. |
| |
| <dl> |
| <dt><h4><pre><code> |
| template<class Derived, class Base> |
| const void_cast_detail::void_caster & |
| void_cast_register( |
| Derived const * derived = NULL, |
| Base * const base = NULL |
| ) |
| </code></pre></h4></dt> |
| <dd> |
| This function "registers" a pair of related types. It stores the fact that |
| <code style="white-space: normal">Derived</code> is immediately derived from |
| <code style="white-space: normal">Base</code> in a global table. |
| <ul> |
| <li>This "registration" can be invoked anywhere in the program. The table is built at |
| pre-runtime and is available anywhere else in the program. |
| <li>only adjacent base/derived pairs need be registered. That is, |
| <pre><code> |
| void_cast_register<A, B>(); |
| void_cast_register<B, C>(); |
| </code></pre> |
| automatically derives the fact that A can be upcast to C and vice-versa. |
| </ul> |
| </dd> |
| |
| <dt><h4><pre><code> |
| void * |
| void_upcast( |
| extended_type_info const & derived_type, |
| extended_type_info const & base_type, |
| void * const t |
| ); |
| </code></pre></h4></dt> |
| |
| <dt><h4><pre><code> |
| void * |
| void_downcast( |
| extended_type_info const & derived_type, |
| extended_type_info const & base_type, |
| void * const t |
| ); |
| </code></pre></h4></dt> |
| <dd> |
| These functions cast a void pointer from one type to another. The source and |
| definition types are specified by passing references to the corresponding |
| <a href="extended_type_info.html"><code style="white-space: normal"> |
| extended_type_info</code></a> |
| records. An attempt to cast between types not "registered" with |
| <code style="white-space: normal">void_cast_register</code> |
| will throw a |
| <a href="exceptions.html"><code style="white-space: normal">boost::archive::archive_exception</code></a> |
| with value equal to |
| <code style="white-space: normal">unregistered_cast</code> |
| </dd> |
| </dl> |
| |
| <hr> |
| <p><i>© Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 2002-2004. |
| Distributed under the Boost Software License, Version 1.0. (See |
| accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
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