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<title>read_at (2 of 8 overloads)</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.read_at.overload2"></a><a class="link" href="overload2.html" title="read_at (2 of 8 overloads)">read_at (2
of 8 overloads)</a>
</h4></div></div></div>
<p>
Attempt to read a certain amount of data at the specified offset before
returning.
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <a class="link" href="../SyncRandomAccessReadDevice.html" title="Buffer-oriented synchronous random-access read device requirements">SyncRandomAccessReadDevice</a><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</a><span class="special">></span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">read_at</span><span class="special">(</span>
<span class="identifier">SyncRandomAccessReadDevice</span> <span class="special">&</span> <span class="identifier">d</span><span class="special">,</span>
<span class="identifier">uint64_t</span> <span class="identifier">offset</span><span class="special">,</span>
<span class="keyword">const</span> <span class="identifier">MutableBufferSequence</span> <span class="special">&</span> <span class="identifier">buffers</span><span class="special">,</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="special">&</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
<p>
This function is used to read a certain number of bytes of data from a
random access device at the specified offset. The call will block until
one of the following conditions is true:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
The supplied buffers are full. That is, the bytes transferred is equal
to the sum of the buffer sizes.
</li>
<li class="listitem">
An error occurred.
</li>
</ul></div>
<p>
This operation is implemented in terms of zero or more calls to the device's
read_some_at function.
</p>
<h6>
<a name="boost_asio.reference.read_at.overload2.h0"></a>
<span class="phrase"><a name="boost_asio.reference.read_at.overload2.parameters"></a></span><a class="link" href="overload2.html#boost_asio.reference.read_at.overload2.parameters">Parameters</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">d</span></dt>
<dd><p>
The device from which the data is to be read. The type must support
the SyncRandomAccessReadDevice concept.
</p></dd>
<dt><span class="term">offset</span></dt>
<dd><p>
The offset at which the data will be read.
</p></dd>
<dt><span class="term">buffers</span></dt>
<dd><p>
One or more buffers into which the data will be read. The sum of
the buffer sizes indicates the maximum number of bytes to read from
the device.
</p></dd>
<dt><span class="term">ec</span></dt>
<dd><p>
Set to indicate what error occurred, if any.
</p></dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.read_at.overload2.h1"></a>
<span class="phrase"><a name="boost_asio.reference.read_at.overload2.return_value"></a></span><a class="link" href="overload2.html#boost_asio.reference.read_at.overload2.return_value">Return Value</a>
</h6>
<p>
The number of bytes transferred.
</p>
<h6>
<a name="boost_asio.reference.read_at.overload2.h2"></a>
<span class="phrase"><a name="boost_asio.reference.read_at.overload2.example"></a></span><a class="link" href="overload2.html#boost_asio.reference.read_at.overload2.example">Example</a>
</h6>
<p>
To read into a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span class="identifier">buffer</span></code></a> function as follows:
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">read_at</span><span class="special">(</span><span class="identifier">d</span><span class="special">,</span> <span class="number">42</span><span class="special">,</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">size</span><span class="special">),</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
<p>
See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span class="identifier">buffer</span></code></a>
documentation for information on reading into multiple buffers in one go,
and how to use it with arrays, boost::array or std::vector.
</p>
<h6>
<a name="boost_asio.reference.read_at.overload2.h3"></a>
<span class="phrase"><a name="boost_asio.reference.read_at.overload2.remarks"></a></span><a class="link" href="overload2.html#boost_asio.reference.read_at.overload2.remarks">Remarks</a>
</h6>
<p>
This overload is equivalent to calling:
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">read_at</span><span class="special">(</span>
<span class="identifier">d</span><span class="special">,</span> <span class="number">42</span><span class="special">,</span> <span class="identifier">buffers</span><span class="special">,</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">transfer_all</span><span class="special">(),</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
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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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