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<div class="titlepage"><div><div><h5 class="title">
<a name="boost_asio.reference.basic_datagram_socket.cancel.overload2"></a><a class="link" href="overload2.html" title="basic_datagram_socket::cancel (2 of 2 overloads)">
          basic_datagram_socket::cancel (2 of 2 overloads)</a>
</h5></div></div></div>
<p>
            <span class="emphasis"><em>Inherited from basic_socket.</em></span>
          </p>
<p>
            Cancel all asynchronous operations associated with the socket.
          </p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">cancel</span><span class="special">(</span>
    <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="special">&amp;</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
<p>
            This function causes all outstanding asynchronous connect, send and receive
            operations to finish immediately, and the handlers for cancelled operations
            will be passed the boost::asio::error::operation_aborted error.
          </p>
<a name="boost_asio.reference.basic_datagram_socket.cancel.overload2.parameters"></a><h6>
<a name="id2900664"></a>
            <a class="link" href="overload2.html#boost_asio.reference.basic_datagram_socket.cancel.overload2.parameters">Parameters</a>
          </h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">ec</span></dt>
<dd><p>
                Set to indicate what error occurred, if any.
              </p></dd>
</dl>
</div>
<a name="boost_asio.reference.basic_datagram_socket.cancel.overload2.remarks"></a><h6>
<a name="id2900705"></a>
            <a class="link" href="overload2.html#boost_asio.reference.basic_datagram_socket.cancel.overload2.remarks">Remarks</a>
          </h6>
<p>
            Calls to cancel() will always fail with boost::asio::error::operation_not_supported
            when run on Windows XP, Windows Server 2003, and earlier versions of
            Windows, unless BOOST_ASIO_ENABLE_CANCELIO is defined. However, the CancelIo
            function has two issues that should be considered before enabling its
            use:
          </p>
<div class="itemizedlist"><ul type="disc">
<li>
              It will only cancel asynchronous operations that were initiated in
              the current thread.
            </li>
<li>
              It can appear to complete without error, but the request to cancel
              the unfinished operations may be silently ignored by the operating
              system. Whether it works or not seems to depend on the drivers that
              are installed.
            </li>
</ul></div>
<p>
            For portable cancellation, consider using one of the following alternatives:
          </p>
<div class="itemizedlist"><ul type="disc">
<li>
              Disable asio's I/O completion port backend by defining BOOST_ASIO_DISABLE_IOCP.
            </li>
<li>
              Use the close() function to simultaneously cancel the outstanding operations
              and close the socket.
            </li>
</ul></div>
<p>
            When running on Windows Vista, Windows Server 2008, and later, the CancelIoEx
            function is always used. This function does not have the problems described
            above.
          </p>
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<td align="right"><div class="copyright-footer">Copyright © 2003 - 2008 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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