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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.overview.windows.random_access_handle"></a><a class="link" href="random_access_handle.html" title="Random-Access HANDLEs"> Random-Access
HANDLEs</a>
</h4></div></div></div>
<p>
Asio provides Windows-specific classes that permit asynchronous read and
write operations to be performed on HANDLEs that refer to regular files.
</p>
<p>
For example, to perform asynchronous operations on a file the following
object may be created:
</p>
<pre class="programlisting"><span class="identifier">HANDLE</span> <span class="identifier">handle</span> <span class="special">=</span> <span class="special">::</span><span class="identifier">CreateFile</span><span class="special">(...);</span>
<span class="identifier">windows</span><span class="special">::</span><span class="identifier">random_access_handle</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">my_io_service</span><span class="special">,</span> <span class="identifier">handle</span><span class="special">);</span>
</pre>
<p>
Data may be read from or written to the handle using one of the <code class="computeroutput"><span class="identifier">read_some_at</span><span class="special">()</span></code>,
<code class="computeroutput"><span class="identifier">async_read_some_at</span><span class="special">()</span></code>,
<code class="computeroutput"><span class="identifier">write_some_at</span><span class="special">()</span></code>
or <code class="computeroutput"><span class="identifier">async_write_some_at</span><span class="special">()</span></code> member functions. However, like the equivalent
functions (<code class="computeroutput"><span class="identifier">read_some</span><span class="special">()</span></code>,
etc.) on streams, these functions are only required to transfer one or
more bytes in a single operation. Therefore free functions called <a class="link" href="../../reference/read_at.html" title="read_at">read_at()</a>, <a class="link" href="../../reference/async_read_at.html" title="async_read_at">async_read_at()</a>,
<a class="link" href="../../reference/write_at.html" title="write_at">write_at()</a> and <a class="link" href="../../reference/async_write_at.html" title="async_write_at">async_write_at()</a>
have been created to repeatedly call the corresponding <code class="literal"><span class="bold"><strong>*</strong></span>_some_at()</code> function until all data has
been transferred.
</p>
<a name="asio.overview.windows.random_access_handle.see_also"></a><h6>
<a name="id487212"></a>
<a class="link" href="random_access_handle.html#asio.overview.windows.random_access_handle.see_also">See
Also</a>
</h6>
<p>
<a class="link" href="../../reference/windows__random_access_handle.html" title="windows::random_access_handle">windows::random_access_handle</a>,
<a class="link" href="../../reference/windows__basic_random_access_handle.html" title="windows::basic_random_access_handle">windows::basic_random_access_handle</a>,
<a class="link" href="../../reference/windows__random_access_handle_service.html" title="windows::random_access_handle_service">windows::random_access_handle_service</a>.
</p>
<a name="asio.overview.windows.random_access_handle.notes"></a><h6>
<a name="id487260"></a>
<a class="link" href="random_access_handle.html#asio.overview.windows.random_access_handle.notes">Notes</a>
</h6>
<p>
Windows random-access <code class="computeroutput"><span class="identifier">HANDLE</span></code>s
are only available at compile time when targeting Windows and only when
the I/O completion port backend is used (which is the default). A program
may test for the macro <code class="computeroutput"><span class="identifier">ASIO_HAS_WINDOWS_RANDOM_ACCESS_HANDLE</span></code>
to determine whether they are supported.
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2003 - 2010 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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