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| <title>pointer_cast.hpp</title> |
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| <h1><IMG height="86" alt="C++ Boost" src="../../boost.png" width="277" align="middle" border="0">Pointer |
| cast functions</h1> |
| <p>The pointer cast functions (<code>boost::static_pointer_cast</code> <code>boost::dynamic_pointer_cast</code> |
| <code>boost::reinterpret_pointer_cast</code> <code>boost::const_pointer_cast</code>) |
| provide a way to write generic pointer castings for raw pointers. The functions |
| are defined in <CITE><A href="../../boost/pointer_cast.hpp">boost/pointer_cast.hpp</A>.</CITE></p> |
| <P>There is test/example code in <CITE><A href="test/pointer_cast_test.cpp">pointer_cast_test.cpp</A></CITE>.</p> |
| <h2><a name="rationale">Rationale</a></h2> |
| <P>Boost smart pointers usually overload those functions to provide a mechanism to |
| emulate pointers casts. For example, <code>boost::shared_ptr<...></code> implements |
| a static pointer cast this way:</P> |
| <pre> |
| template<class T, class U> |
| shared_ptr<T> static_pointer_cast(shared_ptr<U> const &r); |
| </pre> |
| <P>Pointer cast functions from <CITE><A href="../../boost/pointer_cast.hpp">boost/pointer_cast.hpp</A></CITE> |
| are overloads of <code>boost::static_pointer_cast</code>, <code>boost::dynamic_pointer_cast</code>, |
| <code>boost::reinterpret_pointer_cast</code> and <code>boost::const_pointer_cast</code> |
| for raw pointers. This way when developing pointer type independent classes, |
| for example, memory managers or shared memory compatible classes, the same code |
| can be used for raw and smart pointers.</p> |
| <H2><A name="synopsis">Synopsis</A></H2> |
| <BLOCKQUOTE> |
| <PRE> |
| namespace boost { |
| |
| template<class T, class U> |
| inline T* static_pointer_cast(U *ptr) |
| { return static_cast<T*>(ptr); } |
| |
| template<class T, class U> |
| inline T* dynamic_pointer_cast(U *ptr) |
| { return dynamic_cast<T*>(ptr); } |
| |
| template<class T, class U> |
| inline T* const_pointer_cast(U *ptr) |
| { return const_cast<T*>(ptr); } |
| |
| template<class T, class U> |
| inline T* reinterpret_pointer_cast(U *ptr) |
| { return reinterpret_cast<T*>(ptr); } |
| |
| } // namespace boost |
| </PRE> |
| </BLOCKQUOTE> |
| <P>As you can see from the above synopsis, the pointer cast functions are just |
| wrappers around standard C++ cast operators.</P> |
| <H2><A name="example">Example</A></H2> |
| <BLOCKQUOTE> |
| <PRE> |
| #include <boost/pointer_cast.hpp> |
| #include <boost/shared_ptr.hpp> |
| |
| class base |
| { |
| public: |
| |
| virtual ~base() |
| { |
| } |
| }; |
| |
| class derived: public base |
| { |
| }; |
| |
| template <class BasePtr> |
| void check_if_it_is_derived(const BasePtr &ptr) |
| { |
| assert(boost::dynamic_pointer_cast<derived>(ptr) != 0); |
| } |
| |
| int main() |
| { |
| <I>// Create a raw and a shared_ptr</I> |
| |
| base *ptr = new derived; |
| boost::shared_ptr<base> sptr(new derived); |
| |
| <I>// Check that base pointer points actually to derived class</I> |
| |
| check_if_it_is_derived(ptr); |
| check_if_it_is_derived(sptr); |
| |
| // <EM>Ok!</EM> |
| |
| delete ptr; |
| return 0; |
| }</PRE> |
| </BLOCKQUOTE> |
| <P>The example demonstrates how the generic pointer casts help us create pointer |
| independent code.</P> |
| <hr> |
| <p>Revised: $Date: 2005-12-06 08:26:13 -0500 (Tue, 06 Dec 2005) $</p> |
| <p>Copyright 2005 Ion Gaztañaga. Use, modification, and distribution are subject to |
| the Boost Software License, Version 1.0. (See accompanying file <A href="../../LICENSE_1_0.txt"> |
| LICENSE_1_0.txt</A> or a copy at <<A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>>.)</p> |
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