C++ Boost

Serialization

void_cast


Motivation

C++ includes the operator dynamic_cast<T>(U * u) 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 classes would diminish the applicability of the library.

Usage

The following functions are defined in the header void_cast.hpp. They are declared in the namespace boost::serialization.


template<class Derived, class Base>
const void_cast_detail::void_caster &
void_cast_register(
    Derived const * derived = NULL, 
    Base * const base = NULL
)

This function "registers" a pair of related types. It stores the fact that Derived is immediately derived from Base in a global table.


void *
void_upcast(
    extended_type_info const & derived_type,
    extended_type_info const & base_type,
    void * const t 
);


void *
void_downcast(
    extended_type_info const & derived_type,
    extended_type_info const & base_type,
    void * const t 
);

These functions cast a void pointer from one type to another. The source and definition types are specified by passing references to the corresponding extended_type_info records. An attempt to cast between types not "registered" with void_cast_register will throw a boost::archive::archive_exception with value equal to unregistered_cast

© Copyright Robert Ramey 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)