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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.read_at.overload7"></a><a class="link" href="overload7.html" title="read_at (7 of 8 overloads)">read_at (7
        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">&lt;</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> <span class="identifier">Allocator</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">CompletionCondition</span><span class="special">&gt;</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">&amp;</span> <span class="identifier">d</span><span class="special">,</span>
    <span class="identifier">boost</span><span class="special">::</span><span class="identifier">uint64_t</span> <span class="identifier">offset</span><span class="special">,</span>
    <span class="identifier">basic_streambuf</span><span class="special">&lt;</span> <span class="identifier">Allocator</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">b</span><span class="special">,</span>
    <span class="identifier">CompletionCondition</span> <span class="identifier">completion_condition</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" type="disc"><li class="listitem">
              The completion_condition function object returns 0.
            </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.overload7.h0"></a>
          <span><a name="boost_asio.reference.read_at.overload7.parameters"></a></span><a class="link" href="overload7.html#boost_asio.reference.read_at.overload7.parameters">Parameters</a>
        </h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<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">b</span></dt>
<dd><p>
                The <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput"><span class="identifier">basic_streambuf</span></code></a> object into
                which the data will be read.
              </p></dd>
<dt><span class="term">completion_condition</span></dt>
<dd>
<p>
                The function object to be called to determine whether the read operation
                is complete. The signature of the function object must be:
</p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">completion_condition</span><span class="special">(</span>
  <span class="comment">// Result of latest read_some_at operation.</span>
  <span class="keyword">const</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">&amp;</span> <span class="identifier">error</span><span class="special">,</span>

  <span class="comment">// Number of bytes transferred so far.</span>
  <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
<span class="special">);</span>
</pre>
<p>
                A return value of 0 indicates that the read operation is complete.
                A non-zero return value indicates the maximum number of bytes to
                be read on the next call to the device's read_some_at function.
              </p>
</dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.read_at.overload7.h1"></a>
          <span><a name="boost_asio.reference.read_at.overload7.return_value"></a></span><a class="link" href="overload7.html#boost_asio.reference.read_at.overload7.return_value">Return Value</a>
        </h6>
<p>
          The number of bytes transferred.
        </p>
<h6>
<a name="boost_asio.reference.read_at.overload7.h2"></a>
          <span><a name="boost_asio.reference.read_at.overload7.exceptions"></a></span><a class="link" href="overload7.html#boost_asio.reference.read_at.overload7.exceptions">Exceptions</a>
        </h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">boost::system::system_error</span></dt>
<dd><p>
                Thrown on failure.
              </p></dd>
</dl>
</div>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2012 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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