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<title>Buffer-oriented asynchronous random-access read device requirements</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.AsyncRandomAccessReadDevice"></a><a class="link" href="AsyncRandomAccessReadDevice.html" title="Buffer-oriented asynchronous random-access read device requirements">Buffer-oriented
asynchronous random-access read device requirements</a>
</h3></div></div></div>
<p>
In the table below, <code class="computeroutput"><span class="identifier">a</span></code> denotes
an asynchronous random access read device object, <code class="computeroutput"><span class="identifier">o</span></code>
denotes an offset of type <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">uint64_t</span></code>,
<code class="computeroutput"><span class="identifier">mb</span></code> denotes an object satisfying
<a class="link" href="MutableBufferSequence.html" title="Mutable buffer sequence requirements">mutable buffer
sequence</a> requirements, and <code class="computeroutput"><span class="identifier">h</span></code>
denotes an object satisfying <a class="link" href="ReadHandler.html" title="Read handler requirements">read
handler</a> requirements.
</p>
<div class="table">
<a name="boost_asio.reference.AsyncRandomAccessReadDevice.t0"></a><p class="title"><b>Table 1. Buffer-oriented asynchronous random-access read device requirements</b></p>
<div class="table-contents"><table class="table" summary="Buffer-oriented asynchronous random-access read device requirements">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
operation
</p>
</th>
<th>
<p>
type
</p>
</th>
<th>
<p>
semantics, pre/post-conditions
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">get_io_service</span><span class="special">();</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">io_service</span><span class="special">&</span></code>
</p>
</td>
<td>
<p>
Returns the <code class="computeroutput"><span class="identifier">io_service</span></code>
object through which the <code class="computeroutput"><span class="identifier">async_read_some_at</span></code>
handler <code class="computeroutput"><span class="identifier">h</span></code> will
be invoked.
</p>
</td>
</tr>
<tr>
<td>
<p>
<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>
<span class="identifier">mb</span><span class="special">,</span>
<span class="identifier">h</span><span class="special">);</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">void</span></code>
</p>
</td>
<td>
<p>
Initiates an asynchronous operation to read one or more bytes of
data from the device <code class="computeroutput"><span class="identifier">a</span></code>
at the offset <code class="computeroutput"><span class="identifier">o</span></code>.
The operation is performed via the <code class="computeroutput"><span class="identifier">io_service</span></code>
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>
and behaves according to <a class="link" href="asynchronous_operations.html" title="Requirements on asynchronous operations">asynchronous
operation</a> requirements.<br> <br> The mutable buffer
sequence <code class="computeroutput"><span class="identifier">mb</span></code> specifies
memory where the data should be placed. The <code class="computeroutput"><span class="identifier">async_read_some_at</span></code>
operation shall always fill a buffer in the sequence completely
before proceeding to the next.<br> <br> The implementation
shall maintain one or more copies of <code class="computeroutput"><span class="identifier">mb</span></code>
until such time as the read operation no longer requires access
to the memory specified by the buffers in the sequence. The program
must ensure the memory is valid until:<br> <br> — the last copy
of <code class="computeroutput"><span class="identifier">mb</span></code> is destroyed,
or<br> <br> — the handler for the asynchronous read operation
is invoked,<br> <br> whichever comes first.<br> <br> If
the total size of all buffers in the sequence <code class="computeroutput"><span class="identifier">mb</span></code>
is <code class="computeroutput"><span class="number">0</span></code>, the asynchronous
read operation shall complete immediately and pass <code class="computeroutput"><span class="number">0</span></code> as the argument to the handler
that specifies the number of bytes read.
</p>
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</tbody>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2013 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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