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| author | DongHun Kwak <dh0128.kwak@samsung.com> | 2017-09-13 11:08:07 +0900 |
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| committer | DongHun Kwak <dh0128.kwak@samsung.com> | 2017-09-13 11:09:00 +0900 |
| commit | b5c87084afaef42b2d058f68091be31988a6a874 (patch) | |
| tree | adef9a65870a41181687e11d57fdf98e7629de3c /doc/html/conversion | |
| parent | 34bd32e225e2a8a94104489b31c42e5801cc1f4a (diff) | |
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Imported Upstream version 1.64.0upstream/1.64.0
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diff --git a/doc/html/conversion/_polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis.html b/doc/html/conversion/_polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis.html new file mode 100644 index 0000000000..12f1dc69ea --- /dev/null +++ b/doc/html/conversion/_polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis.html @@ -0,0 +1,70 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>polymorphic_cast, polymorphic_downcast, polymorphic_pointer_cast and polymorphic_pointer_downcast synopsis</title> +<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> +<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> +<link rel="up" href="../conversion.html" title="Chapter 11. The Conversion Library 1.6"> +<link rel="prev" href="polymorphic_casts.html" title="Polymorphic casts"> +<link rel="next" href="_polymorphic_downcast__example.html" title="polymorphic_downcast example"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> +<table cellpadding="2" width="100%"><tr> +<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> +<td align="center"><a href="../../../index.html">Home</a></td> +<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> +<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> +<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> +<td align="center"><a href="../../../more/index.htm">More</a></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="polymorphic_casts.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../conversion.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="_polymorphic_downcast__example.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +<div class="section"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="conversion._polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis"></a><a class="link" href="_polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis.html" title="polymorphic_cast, polymorphic_downcast, polymorphic_pointer_cast and polymorphic_pointer_downcast synopsis"><code class="computeroutput">polymorphic_cast</code>, + <code class="computeroutput">polymorphic_downcast</code>, <code class="computeroutput">polymorphic_pointer_cast</code> and + <code class="computeroutput">polymorphic_pointer_downcast</code> synopsis</a> +</h2></div></div></div> +<pre class="programlisting">namespace boost { + +template <class Derived, class Base> +inline Derived polymorphic_cast(Base* x); +// Throws: std::bad_cast if ( dynamic_cast<Derived>(x) == 0 ) +// Returns: dynamic_cast<Derived>(x) + +template <class Derived, class Base> +inline Derived polymorphic_downcast(Base* x); +// Effects: assert( dynamic_cast<Derived>(x) == x ); +// Returns: static_cast<Derived>(x) + +template <class Derived, class Base> +inline auto polymorphic_pointer_cast(Base x); +// Throws: std::bad_cast if ( dynamic_pointer_cast<Derived>(x) == 0 ) +// Returns: dynamic_pointer_cast<Derived>(x) + +template <class Derived, class Base> +inline auto polymorphic_pointer_downcast(Base x); +// Effects: assert( dynamic_pointer_cast<Derived>(x) == x ); +// Returns: static_pointer_cast<Derived>(x) + +} +</pre> +</div> +<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> +<td align="left"></td> +<td align="right"><div class="copyright-footer">Copyright © 2001 Beman Dawes<p> + Distributed under the Boost Software License, Version 1.0. (See accompanying + file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) + </p> +</div></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="polymorphic_casts.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../conversion.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="_polymorphic_downcast__example.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> diff --git a/doc/html/conversion/_polymorphic_downcast__example.html b/doc/html/conversion/_polymorphic_downcast__example.html new file mode 100644 index 0000000000..b942a73933 --- /dev/null +++ b/doc/html/conversion/_polymorphic_downcast__example.html @@ -0,0 +1,56 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>polymorphic_downcast example</title> +<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> +<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> +<link rel="up" href="../conversion.html" title="Chapter 11. The Conversion Library 1.6"> +<link rel="prev" href="_polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis.html" title="polymorphic_cast, polymorphic_downcast, polymorphic_pointer_cast and polymorphic_pointer_downcast synopsis"> +<link rel="next" href="_polymorphic_pointer_downcast__example.html" title="polymorphic_pointer_downcast example"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> +<table cellpadding="2" width="100%"><tr> +<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> +<td align="center"><a href="../../../index.html">Home</a></td> +<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> +<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> +<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> +<td align="center"><a href="../../../more/index.htm">More</a></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="_polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../conversion.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="_polymorphic_pointer_downcast__example.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +<div class="section"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="conversion._polymorphic_downcast__example"></a><a class="link" href="_polymorphic_downcast__example.html" title="polymorphic_downcast example"><code class="computeroutput">polymorphic_downcast</code> + example</a> +</h2></div></div></div> +<pre class="programlisting">#include <boost/polymorphic_cast.hpp> +... +class Fruit { public: virtual ~Fruit(){}; ... }; +class Banana : public Fruit { ... }; +... +void f( Fruit * fruit ) { + // ... logic which leads us to believe it is a Banana + Banana * banana = boost::polymorphic_downcast<Banana*>(fruit); + ... +} +</pre> +</div> +<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> +<td align="left"></td> +<td align="right"><div class="copyright-footer">Copyright © 2001 Beman Dawes<p> + Distributed under the Boost Software License, Version 1.0. (See accompanying + file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) + </p> +</div></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="_polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../conversion.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="_polymorphic_pointer_downcast__example.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> diff --git a/doc/html/conversion/_polymorphic_pointer_downcast__example.html b/doc/html/conversion/_polymorphic_pointer_downcast__example.html new file mode 100644 index 0000000000..c40015482a --- /dev/null +++ b/doc/html/conversion/_polymorphic_pointer_downcast__example.html @@ -0,0 +1,63 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>polymorphic_pointer_downcast example</title> +<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> +<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> +<link rel="up" href="../conversion.html" title="Chapter 11. The Conversion Library 1.6"> +<link rel="prev" href="_polymorphic_downcast__example.html" title="polymorphic_downcast example"> +<link rel="next" href="history.html" title="History"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> +<table cellpadding="2" width="100%"><tr> +<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> +<td align="center"><a href="../../../index.html">Home</a></td> +<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> +<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> +<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> +<td align="center"><a href="../../../more/index.htm">More</a></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="_polymorphic_downcast__example.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../conversion.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="history.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +<div class="section"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="conversion._polymorphic_pointer_downcast__example"></a><a class="link" href="_polymorphic_pointer_downcast__example.html" title="polymorphic_pointer_downcast example"><code class="computeroutput">polymorphic_pointer_downcast</code> + example</a> +</h2></div></div></div> +<pre class="programlisting">#include <boost/polymorphic_pointer_cast.hpp> + +class Fruit { public: virtual ~Fruit(){} }; +class Banana : public Fruit {}; + +// use one of these: + +typedef Fruit* FruitPtr; +typedef std::shared_ptr<Fruit> FruitPtr; +typedef boost::shared_ptr<Fruit> FruitPtr; +typedef boost::intrusive_ptr<Fruit> FruitPtr; + +void f(FruitPtr fruit) { + // ... logic which leads us to believe it is a banana + auto banana = boost::polymorphic_pointer_downcast<Banana>(fruit); + ... +} +</pre> +</div> +<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> +<td align="left"></td> +<td align="right"><div class="copyright-footer">Copyright © 2001 Beman Dawes<p> + Distributed under the Boost Software License, Version 1.0. (See accompanying + file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) + </p> +</div></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="_polymorphic_downcast__example.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../conversion.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="history.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> diff --git a/doc/html/conversion/history.html b/doc/html/conversion/history.html new file mode 100644 index 0000000000..1ff9cac8a0 --- /dev/null +++ b/doc/html/conversion/history.html @@ -0,0 +1,61 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>History</title> +<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> +<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> +<link rel="up" href="../conversion.html" title="Chapter 11. The Conversion Library 1.6"> +<link rel="prev" href="_polymorphic_pointer_downcast__example.html" title="polymorphic_pointer_downcast example"> +<link rel="next" href="../date_time.html" title="Chapter 12. Boost.Date_Time"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> +<table cellpadding="2" width="100%"><tr> +<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> +<td align="center"><a href="../../../index.html">Home</a></td> +<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> +<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> +<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> +<td align="center"><a href="../../../more/index.htm">More</a></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="_polymorphic_pointer_downcast__example.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../conversion.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../date_time.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +<div class="section"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="conversion.history"></a><a class="link" href="history.html" title="History">History</a> +</h2></div></div></div> +<p> + <code class="computeroutput">polymorphic_cast</code> was suggested by Bjarne Stroustrup in "The + C++ Programming Language". + </p> +<p> + <code class="computeroutput">polymorphic_downcast</code> was contributed by <a href="http://www.boost.org/people/dave_abrahams.htm" target="_top">Dave + Abrahams</a>. + </p> +<p> + <code class="computeroutput">polymorphic_pointer_downcast</code> was contributed by <a href="http://www.boost.org/people/boris_rasin.htm" target="_top">Boris + Rasin</a> and <code class="computeroutput">polymorphic_pointer_cast</code> by Antony Polukhin. + </p> +<p> + An old numeric_cast that was contributed by <a href="http://www.boost.org/people/kevlin_henney.htm" target="_top">Kevlin + Henney</a> is now superseeded by the <a href="../../../numeric_conversion/doc/html/html/boost_numericconversion/improved_numeric_cast__.html" target="_top">Boost + Numeric Conversion Library</a> + </p> +</div> +<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> +<td align="left"></td> +<td align="right"><div class="copyright-footer">Copyright © 2001 Beman Dawes<p> + Distributed under the Boost Software License, Version 1.0. (See accompanying + file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) + </p> +</div></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="_polymorphic_pointer_downcast__example.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../conversion.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../date_time.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> diff --git a/doc/html/conversion/polymorphic_casts.html b/doc/html/conversion/polymorphic_casts.html new file mode 100644 index 0000000000..3982c3264a --- /dev/null +++ b/doc/html/conversion/polymorphic_casts.html @@ -0,0 +1,131 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>Polymorphic casts</title> +<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> +<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> +<link rel="up" href="../conversion.html" title="Chapter 11. The Conversion Library 1.6"> +<link rel="prev" href="../conversion.html" title="Chapter 11. The Conversion Library 1.6"> +<link rel="next" href="_polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis.html" title="polymorphic_cast, polymorphic_downcast, polymorphic_pointer_cast and polymorphic_pointer_downcast synopsis"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> +<table cellpadding="2" width="100%"><tr> +<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> +<td align="center"><a href="../../../index.html">Home</a></td> +<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> +<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> +<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> +<td align="center"><a href="../../../more/index.htm">More</a></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="../conversion.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../conversion.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="_polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +<div class="section"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="conversion.polymorphic_casts"></a><a class="link" href="polymorphic_casts.html" title="Polymorphic casts">Polymorphic casts</a> +</h2></div></div></div> +<p> + Pointers to polymorphic objects (objects of classes which define at least one + virtual function) are sometimes downcast or crosscast. Downcasting means casting + from a base class to a derived class. Crosscasting means casting across an + inheritance hierarchy diagram, such as from one base to the other in a <code class="literal">Y</code> + diagram hierarchy. + </p> +<p> + Such casts can be done with old-style casts, but this approach is never to + be recommended. Old-style casts are sorely lacking in type safety, suffer poor + readability, and are difficult to locate with search tools. + </p> +<p> + <a name="polymorphic_downcast"></a>The C++ built-in <code class="computeroutput">static_cast</code> + can be used for efficiently downcasting pointers to polymorphic objects, but + provides no error detection for the case where the pointer being cast actually + points to the wrong derived class. The <code class="computeroutput">polymorphic_downcast</code> template + retains the efficiency of <code class="computeroutput">static_cast</code> for non-debug compilations, + but for debug compilations adds safety via an <code class="computeroutput">assert()</code> that a + <code class="computeroutput">dynamic_cast</code> succeeds. + </p> +<p> + A <code class="computeroutput">polymorphic_downcast</code> should be used for downcasts that you are + certain should succeed. Error checking is only performed in translation units + where <code class="computeroutput">NDEBUG</code> is not defined, via + </p> +<pre class="programlisting">assert( dynamic_cast<Derived>(x) == x ) +</pre> +<p> + where <code class="computeroutput">x</code> is the source pointer. This approach ensures that not + only is a non-zero pointer returned, but also that it is correct in the presence + of multiple inheritance. Attempts to crosscast using <code class="computeroutput">polymorphic_downcast</code> + will fail to compile. + </p> +<div class="warning"><table border="0" summary="Warning"> +<tr> +<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td> +<th align="left">Warning</th> +</tr> +<tr><td align="left" valign="top"><p> + Because <code class="computeroutput">polymorphic_downcast</code> uses <code class="computeroutput">assert()</code>, it + violates the One Definition Rule (ODR) if NDEBUG is inconsistently defined + across translation units. See ISO Std 3.2 + </p></td></tr> +</table></div> +<p> + <a name="polymorphic_cast"></a>The C++ built-in <code class="computeroutput">dynamic_cast</code> can + be used for downcasts and crosscasts of pointers to polymorphic objects, but + error notification in the form of a returned value of 0 is inconvenient to + test, or worse yet, easy to forget to test. The throwing form of <code class="computeroutput">dynamic_cast</code>, + which works on references, can be used on pointers through the ugly expression + <code class="computeroutput">&dynamic_cast<T&>(*p), which causes undefined behavior + if </code>p<code class="computeroutput"> is </code>0<code class="computeroutput">. The </code>polymorphic_cast<code class="computeroutput"> template + performs a </code>dynamic_cast<code class="computeroutput"> on a pointer, and throws an exception + if the </code>dynamic_cast` returns 0. + </p> +<p> + For crosscasts, or when the success of a cast can only be known at runtime, + or when efficiency is not important, <code class="computeroutput">polymorphic_cast</code> is preferred. + </p> +<p> + The C++ built-in dynamic_cast must be used to cast references rather than pointers. + It is also the only cast that can be used to check whether a given interface + is supported; in that case a return of 0 isn't an error condition. + </p> +<p> + <a name="polymorphic_pointer_cast"></a>While polymorphic_downcast and polymorphic_cast + work with built-in pointer types only, polymorphic_pointer_downcast and polymorphic_pointer_cast + are more generic versions with support for any pointer type for which the following + expressions would be valid: + </p> +<p> + For <code class="computeroutput">polymorphic_pointer_downcast</code>: + </p> +<pre class="programlisting">static_pointer_cast<Derived>(p); +dynamic_pointer_cast<Derived>(p); +</pre> +<p> + For <code class="computeroutput">polymorphic_pointer_cast</code>: + </p> +<pre class="programlisting">dynamic_pointer_cast<Derived>(p); +!p; // conversion to bool with negation +</pre> +<p> + This includes C++ built-in pointers, <code class="computeroutput">std::shared_ptr</code>, <code class="computeroutput">boost::shared_ptr</code>, + <code class="computeroutput">boost::intrusive_ptr</code>, etc. + </p> +</div> +<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> +<td align="left"></td> +<td align="right"><div class="copyright-footer">Copyright © 2001 Beman Dawes<p> + Distributed under the Boost Software License, Version 1.0. (See accompanying + file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) + </p> +</div></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="../conversion.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../conversion.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="_polymorphic_cast____polymorphic_downcast____polymorphic_pointer_cast__and__polymorphic_pointer_downcast__synopsis.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> |