134 lines
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134 lines
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<title>Buffer-oriented asynchronous random-access read device requirements</title>
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<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../asio.png"></td></tr></table>
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<a accesskey="p" href="AcceptToken.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../home.png" alt="Home"></a><a accesskey="n" href="AsyncRandomAccessWriteDevice.html"><img src="../../next.png" alt="Next"></a>
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<div class="titlepage"><div><div><h3 class="title">
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<a name="asio.reference.AsyncRandomAccessReadDevice"></a><a class="link" href="AsyncRandomAccessReadDevice.html" title="Buffer-oriented asynchronous random-access read device requirements">Buffer-oriented
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asynchronous random-access read device requirements</a>
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</h3></div></div></div>
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<p>
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In the table below, <code class="computeroutput"><span class="identifier">a</span></code> denotes
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an asynchronous random access read device object, <code class="computeroutput"><span class="identifier">o</span></code>
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denotes an offset of type <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">uint64_t</span></code>,
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<code class="computeroutput"><span class="identifier">mb</span></code> denotes an object satisfying
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<a class="link" href="MutableBufferSequence.html" title="Mutable buffer sequence requirements">mutable buffer sequence</a>
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requirements, and <code class="computeroutput"><span class="identifier">h</span></code> denotes
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an object satisfying <a class="link" href="ReadHandler.html" title="Read handler requirements">read handler</a>
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requirements.
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</p>
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<div class="table">
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<a name="asio.reference.AsyncRandomAccessReadDevice.t0"></a><p class="title"><b>Table 4. Buffer-oriented asynchronous random-access read device requirements</b></p>
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<div class="table-contents"><table class="table" summary="Buffer-oriented asynchronous random-access read device requirements">
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<colgroup>
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<col>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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operation
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</p>
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</th>
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<th>
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<p>
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type
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</p>
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</th>
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<th>
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<p>
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semantics, pre/post-conditions
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">get_executor</span><span class="special">()</span></code>
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</p>
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</td>
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<td>
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<p>
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A type satisfying the <a class="link" href="Executor1.html" title="Executor requirements">Executor
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requirements</a>.
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</p>
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</td>
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<td>
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<p>
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Returns the associated I/O executor.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">async_read_some_at</span><span class="special">(</span><span class="identifier">o</span><span class="special">,</span>
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<span class="identifier">mb</span><span class="special">,</span>
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<span class="identifier">h</span><span class="special">);</span></code>
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</p>
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</td>
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<td>
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<p>
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<code class="computeroutput"><span class="keyword">void</span></code>
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</p>
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</td>
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<td>
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<p>
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Initiates an asynchronous operation to read one or more bytes of
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data from the device <code class="computeroutput"><span class="identifier">a</span></code>
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at the offset <code class="computeroutput"><span class="identifier">o</span></code>.
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The operation is performed via the <code class="computeroutput"><span class="identifier">io_service</span></code>
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object <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">get_io_service</span><span class="special">()</span></code>
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and behaves according to <a class="link" href="asynchronous_operations.html" title="Requirements on asynchronous operations">asynchronous
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operation</a> requirements.<br> <br> The mutable buffer
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sequence <code class="computeroutput"><span class="identifier">mb</span></code> specifies
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memory where the data should be placed. The <code class="computeroutput"><span class="identifier">async_read_some_at</span></code>
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operation shall always fill a buffer in the sequence completely
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before proceeding to the next.<br> <br> The implementation
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shall maintain one or more copies of <code class="computeroutput"><span class="identifier">mb</span></code>
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until such time as the read operation no longer requires access
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to the memory specified by the buffers in the sequence. The program
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must ensure the memory is valid until:<br> <br> — the last copy
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of <code class="computeroutput"><span class="identifier">mb</span></code> is destroyed,
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or<br> <br> — the handler for the asynchronous read operation
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is invoked,<br> <br> whichever comes first.<br> <br> If
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the total size of all buffers in the sequence <code class="computeroutput"><span class="identifier">mb</span></code>
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is <code class="computeroutput"><span class="number">0</span></code>, the asynchronous
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read operation shall complete immediately and pass <code class="computeroutput"><span class="number">0</span></code> as the argument to the handler
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that specifies the number of bytes read.
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</p>
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</td>
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</tr>
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</tbody>
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</table></div>
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</div>
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<br class="table-break">
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</div>
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<div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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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</p>
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</div>
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