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129 lines
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<title>Buffer-oriented synchronous 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="SignalToken.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="SyncRandomAccessWriteDevice.html"><img src="../../next.png" alt="Next"></a>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="asio.reference.SyncRandomAccessReadDevice"></a><a class="link" href="SyncRandomAccessReadDevice.html" title="Buffer-oriented synchronous random-access read device requirements">Buffer-oriented
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synchronous 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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a synchronous 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">ec</span></code> denotes
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an object of type <code class="computeroutput"><span class="identifier">error_code</span></code>.
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</p>
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<div class="table">
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<a name="asio.reference.SyncRandomAccessReadDevice.t0"></a><p class="title"><b>Table 30. Buffer-oriented synchronous random-access read device requirements</b></p>
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<div class="table-contents"><table class="table" summary="Buffer-oriented synchronous random-access read device requirements">
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<colgroup>
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<col>
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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">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></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="identifier">size_t</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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Equivalent to:
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</p>
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<pre class="programlisting"><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">;</span>
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<span class="identifier">size_t</span> <span class="identifier">s</span> <span class="special">=</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">read_some_at</span><span class="special">(</span><span class="identifier">o</span><span class="special">,</span> <span class="identifier">mb</span><span class="special">,</span> <span class="identifier">ec</span><span class="special">);</span>
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<span class="keyword">if</span> <span class="special">(</span><span class="identifier">ec</span><span class="special">)</span> <span class="keyword">throw</span> <span class="identifier">system_error</span><span class="special">(</span><span class="identifier">ec</span><span class="special">);</span>
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<span class="keyword">return</span> <span class="identifier">s</span><span class="special">;</span>
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</pre>
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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">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">ec</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="identifier">size_t</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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Reads one or more bytes of data from the device <code class="computeroutput"><span class="identifier">a</span></code>
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at offset <code class="computeroutput"><span class="identifier">o</span></code>.<br>
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<br> The mutable buffer sequence <code class="computeroutput"><span class="identifier">mb</span></code>
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specifies memory where the data should be placed. The <code class="computeroutput"><span class="identifier">read_some_at</span></code> operation shall
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always fill a buffer in the sequence completely before proceeding
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to the next.<br> <br> If successful, returns the number of
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bytes read and sets <code class="computeroutput"><span class="identifier">ec</span></code>
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such that <code class="computeroutput"><span class="special">!</span><span class="identifier">ec</span></code>
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is true. If an error occurred, returns <code class="computeroutput"><span class="number">0</span></code>
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and sets <code class="computeroutput"><span class="identifier">ec</span></code> such
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that <code class="computeroutput"><span class="special">!!</span><span class="identifier">ec</span></code>
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is true.<br> <br> If the total size of all buffers in the sequence
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<code class="computeroutput"><span class="identifier">mb</span></code> is <code class="computeroutput"><span class="number">0</span></code>, the function shall return <code class="computeroutput"><span class="number">0</span></code> immediately.
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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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<hr>
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<div class="spirit-nav">
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