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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.overview.windows.random_access_handle"></a><a class="link" href="random_access_handle.html" title="Random-Access HANDLEs">Random-Access
  28         HANDLEs</a>
  29 </h4></div></div></div>
  30 <p>
  31           Boost.Asio provides Windows-specific classes that permit asynchronous read
  32           and write operations to be performed on HANDLEs that refer to regular files.
  33         </p>
  34 <p>
  35           For example, to perform asynchronous operations on a file the following
  36           object may be created:
  37         </p>
  38 <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>
  39 <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>
  40 </pre>
  41 <p>
  42           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>,
  43           <code class="computeroutput"><span class="identifier">async_read_some_at</span><span class="special">()</span></code>,
  44           <code class="computeroutput"><span class="identifier">write_some_at</span><span class="special">()</span></code>
  45           or <code class="computeroutput"><span class="identifier">async_write_some_at</span><span class="special">()</span></code> member functions. However, like the equivalent
  46           functions (<code class="computeroutput"><span class="identifier">read_some</span><span class="special">()</span></code>,
  47           etc.) on streams, these functions are only required to transfer one or
  48           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>,
  49           <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
  50           been created to repeatedly call the corresponding <code class="literal"><span class="bold"><strong>*</strong></span>_some_at()</code>
  51           function until all data has been transferred.
  52         </p>
  53 <h6>
  54 <a name="boost_asio.overview.windows.random_access_handle.h0"></a>
  55           <span class="phrase"><a name="boost_asio.overview.windows.random_access_handle.see_also"></a></span><a class="link" href="random_access_handle.html#boost_asio.overview.windows.random_access_handle.see_also">See
  56           Also</a>
  57         </h6>
  58 <p>
  59           <a class="link" href="../../reference/windows__random_access_handle.html" title="windows::random_access_handle">windows::random_access_handle</a>,
  60           <a class="link" href="../../reference/windows__basic_random_access_handle.html" title="windows::basic_random_access_handle">windows::basic_random_access_handle</a>,
  61           <a class="link" href="../../reference/windows__random_access_handle_service.html" title="windows::random_access_handle_service">windows::random_access_handle_service</a>.
  62         </p>
  63 <h6>
  64 <a name="boost_asio.overview.windows.random_access_handle.h1"></a>
  65           <span class="phrase"><a name="boost_asio.overview.windows.random_access_handle.notes"></a></span><a class="link" href="random_access_handle.html#boost_asio.overview.windows.random_access_handle.notes">Notes</a>
  66         </h6>
  67 <p>
  68           Windows random-access <code class="computeroutput"><span class="identifier">HANDLE</span></code>s
  69           are only available at compile time when targeting Windows and only when
  70           the I/O completion port backend is used (which is the default). A program
  71           may test for the macro <code class="computeroutput"><span class="identifier">BOOST_ASIO_HAS_WINDOWS_RANDOM_ACCESS_HANDLE</span></code>
  72           to determine whether they are supported.
  73         </p>
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