<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>use_future_t</title> <link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> <link rel="home" href="../../boost_asio.html" title="Boost.Asio"> <link rel="up" href="../reference.html" title="Reference"> <link rel="prev" href="use_future.html" title="use_future"> <link rel="next" href="use_future_t/allocator_type.html" title="use_future_t::allocator_type"> </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="use_future.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="use_future_t/allocator_type.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="boost_asio.reference.use_future_t"></a><a class="link" href="use_future_t.html" title="use_future_t">use_future_t</a> </h3></div></div></div> <p> Class used to specify that an asynchronous operation should return a future. </p> <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">Allocator</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span><span class="special"><</span><span class="keyword">void</span><span class="special">>></span> <span class="keyword">class</span> <span class="identifier">use_future_t</span> </pre> <h5> <a name="boost_asio.reference.use_future_t.h0"></a> <span class="phrase"><a name="boost_asio.reference.use_future_t.types"></a></span><a class="link" href="use_future_t.html#boost_asio.reference.use_future_t.types">Types</a> </h5> <div class="informaltable"><table class="table"> <colgroup> <col> <col> </colgroup> <thead><tr> <th> <p> Name </p> </th> <th> <p> Description </p> </th> </tr></thead> <tbody><tr> <td> <p> <a class="link" href="use_future_t/allocator_type.html" title="use_future_t::allocator_type"><span class="bold"><strong>allocator_type</strong></span></a> </p> </td> <td> <p> The allocator type. The allocator is used when constructing the std::promise object for a given asynchronous operation. </p> </td> </tr></tbody> </table></div> <h5> <a name="boost_asio.reference.use_future_t.h1"></a> <span class="phrase"><a name="boost_asio.reference.use_future_t.member_functions"></a></span><a class="link" href="use_future_t.html#boost_asio.reference.use_future_t.member_functions">Member Functions</a> </h5> <div class="informaltable"><table class="table"> <colgroup> <col> <col> </colgroup> <thead><tr> <th> <p> Name </p> </th> <th> <p> Description </p> </th> </tr></thead> <tbody> <tr> <td> <p> <a class="link" href="use_future_t/get_allocator.html" title="use_future_t::get_allocator"><span class="bold"><strong>get_allocator</strong></span></a> </p> </td> <td> <p> Obtain allocator. </p> </td> </tr> <tr> <td> <p> <a class="link" href="use_future_t/operator_lb__rb_.html" title="use_future_t::operator[]"><span class="bold"><strong>operator[]</strong></span></a> </p> </td> <td> <p> Specify an alternate allocator. </p> </td> </tr> <tr> <td> <p> <a class="link" href="use_future_t/use_future_t.html" title="use_future_t::use_future_t"><span class="bold"><strong>use_future_t</strong></span></a> </p> </td> <td> <p> Construct using default-constructed allocator. </p> <p> Construct using specified allocator. </p> </td> </tr> </tbody> </table></div> <p> The <a class="link" href="use_future_t.html" title="use_future_t"><code class="computeroutput"><span class="identifier">use_future_t</span></code></a> class is used to indicate that an asynchronous operation should return a std::future object. A <a class="link" href="use_future_t.html" title="use_future_t"><code class="computeroutput"><span class="identifier">use_future_t</span></code></a> object may be passed as a handler to an asynchronous operation, typically using the special value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span></code>. For example: </p> <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">my_future</span> <span class="special">=</span> <span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span><span class="special">);</span> </pre> <p> The initiating function (async_read_some in the above example) returns a future that will receive the result of the operation. If the operation completes with an error_code indicating failure, it is converted into a system_error and passed back to the caller via the future. </p> <h5> <a name="boost_asio.reference.use_future_t.h2"></a> <span class="phrase"><a name="boost_asio.reference.use_future_t.requirements"></a></span><a class="link" href="use_future_t.html#boost_asio.reference.use_future_t.requirements">Requirements</a> </h5> <p> <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/use_future.hpp</code> </p> <p> <span class="emphasis"><em>Convenience header: </em></span>None </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 © 2003-2015 Christopher M. Kohlhoff<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="use_future.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="use_future_t/allocator_type.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>