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100 lines
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<html>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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<title>Movable I/O Objects</title>
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<link rel="stylesheet" href="../../../boostbook.css" type="text/css">
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<link rel="up" href="../cpp2011.html" title="C++ 2011 Support">
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<link rel="next" href="move_handlers.html" title="Movable Handlers">
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../../asio.png"></td></tr></table>
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<div class="spirit-nav">
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<a accesskey="p" href="system_error.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../cpp2011.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="move_handlers.html"><img src="../../../next.png" alt="Next"></a>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="asio.overview.cpp2011.move_objects"></a><a class="link" href="move_objects.html" title="Movable I/O Objects">Movable I/O Objects</a>
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</h4></div></div></div>
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<p>
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When move support is available (via rvalue references), Asio allows move
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construction and assignment of sockets, serial ports, POSIX descriptors
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and Windows handles.
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</p>
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<p>
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Move support allows you to write code like:
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</p>
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<pre class="programlisting"><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">make_socket</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">&</span> <span class="identifier">i</span><span class="special">)</span>
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<span class="special">{</span>
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<span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">s</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>
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<span class="special">...</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">s</span><span class="special">);</span>
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<span class="special">}</span>
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</pre>
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<p>
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or:
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</p>
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<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">connection</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">enable_shared_from_this</span><span class="special"><</span><span class="identifier">connection</span><span class="special">></span>
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<span class="special">{</span>
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<span class="keyword">private</span><span class="special">:</span>
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<span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">local_socket</span><span class="special">;</span>
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<span class="special">...</span>
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<span class="keyword">public</span><span class="special">:</span>
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<span class="identifier">connection</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&&</span> <span class="identifier">s</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">local_socket</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">s</span><span class="special">))</span> <span class="special">{}</span>
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<span class="special">...</span>
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<span class="special">};</span>
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<span class="special">...</span>
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<span class="keyword">class</span> <span class="identifier">server</span>
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<span class="special">{</span>
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<span class="keyword">private</span><span class="special">:</span>
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<span class="identifier">tcp</span><span class="special">::</span><span class="identifier">acceptor</span> <span class="identifier">acceptor_</span><span class="special">;</span>
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<span class="special">...</span>
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<span class="keyword">void</span> <span class="identifier">handle_accept</span><span class="special">(</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket</span><span class="special">)</span>
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<span class="special">{</span>
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<span class="keyword">if</span> <span class="special">(!</span><span class="identifier">ec</span><span class="special">)</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">make_shared</span><span class="special"><</span><span class="identifier">connection</span><span class="special">>(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">socket</span><span class="special">))-></span><span class="identifier">go</span><span class="special">();</span>
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<span class="identifier">acceptor_</span><span class="special">.</span><span class="identifier">async_accept</span><span class="special">(...);</span>
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<span class="special">}</span>
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<span class="special">...</span>
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<span class="special">};</span>
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</pre>
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<p>
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as well as:
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</p>
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<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">></span> <span class="identifier">sockets</span><span class="special">;</span>
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<span class="identifier">sockets</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">(...));</span>
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</pre>
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<p>
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A word of warning: There is nothing stopping you from moving these objects
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while there are pending asynchronous operations, but it is unlikely to
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be a good idea to do so. In particular, composed operations like <a class="link" href="../../reference/async_read.html" title="async_read">async_read()</a> store a reference
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to the stream object. Moving during the composed operation means that the
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composed operation may attempt to access a moved-from object.
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</p>
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<p>
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Move support is automatically enabled for <code class="literal">g++</code> 4.5 and
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later, when the <code class="literal">-std=c++0x</code> or <code class="literal">-std=gnu++0x</code>
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compiler options are used. It may be disabled by defining <code class="computeroutput"><span class="identifier">ASIO_DISABLE_MOVE</span></code>, or explicitly enabled
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for other compilers by defining <code class="computeroutput"><span class="identifier">ASIO_HAS_MOVE</span></code>.
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Note that these macros also affect the availability of <a class="link" href="move_handlers.html" title="Movable Handlers">movable
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handlers</a>.
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</p>
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</div>
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<div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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>)
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</p>
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</div>
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