futures.html
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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.overview.cpp2011.futures"></a><a class="link" href="futures.html" title="Futures">Futures</a>
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<p>
The <code class="computeroutput">asio::use_future</code> special value provides first-class support
for returning a C++11 <code class="computeroutput">std::future</code> from an asynchronous operation's
initiating function.
</p>
<p>
To use <code class="computeroutput">asio::use_future</code>, pass it to an asynchronous operation
instead of a normal completion handler. For example:
</p>
<pre class="programlisting">std::future<std::size_t> length =
my_socket.async_read_some(my_buffer, asio::use_future);
</pre>
<p>
Where a handler signature has the form:
</p>
<pre class="programlisting">void handler(asio::error_code ec, result_type result);
</pre>
<p>
the initiating function returns a <code class="computeroutput">std::future</code> templated on
<code class="computeroutput">result_type</code>. In the above example, this is <code class="computeroutput">std::size_t</code>.
If the asynchronous operation fails, the <code class="computeroutput">error_code</code> is converted
into a <code class="computeroutput">system_error</code> exception and passed back to the caller
through the future.
</p>
<p>
Where a handler signature has the form:
</p>
<pre class="programlisting">void handler(asio::error_code ec);
</pre>
<p>
the initiating function returns <code class="computeroutput">std::future<void></code>. As
above, an error is passed back in the future as a <code class="computeroutput">system_error</code>
exception.
</p>
<p>
<a class="link" href="../../reference/use_future.html" title="use_future">use_future</a>, <a class="link" href="../../reference/use_future_t.html" title="use_future_t">use_future_t</a>,
<a class="link" href="../../examples/cpp11_examples.html#asio.examples.cpp11_examples.futures">Futures example (C++11)</a>.
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<td align="right"><div class="copyright-footer">Copyright © 2003-2020 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>)
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