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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 6 overloads)">read_at (2 |
| of 6 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="keyword">typename</span> <span class="identifier">CompletionCondition</span><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">boost</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">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 supplied buffers are full. That is, the bytes transferred is equal |
| to the sum of the buffer sizes. |
| </li> |
| <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> |
| <a name="boost_asio.reference.read_at.overload2.parameters"></a><h6> |
| <a name="id1291178"></a> |
| <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> |
| <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">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">&</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> |
| <a name="boost_asio.reference.read_at.overload2.return_value"></a><h6> |
| <a name="id1291384"></a> |
| <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> |
| <a name="boost_asio.reference.read_at.overload2.exceptions"></a><h6> |
| <a name="id1291410"></a> |
| <a class="link" href="overload2.html#boost_asio.reference.read_at.overload2.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> |
| <a name="boost_asio.reference.read_at.overload2.example"></a><h6> |
| <a name="id1291453"></a> |
| <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">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">transfer_at_least</span><span class="special">(</span><span class="number">32</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> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2003 - 2010 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>) |
| </p> |
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