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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.write_at.overload3"></a><a class="link" href="overload3.html" title="write_at (3 of 8 overloads)">write_at (3
  28         of 8 overloads)</a>
  29 </h4></div></div></div>
  30 <p>
  31           Write a certain amount of data at a specified offset before returning.
  32         </p>
  33 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
  34     <span class="keyword">typename</span> <a class="link" href="../SyncRandomAccessWriteDevice.html" title="Buffer-oriented synchronous random-access write device requirements">SyncRandomAccessWriteDevice</a><span class="special">,</span>
  35     <span class="keyword">typename</span> <a class="link" href="../ConstBufferSequence.html" title="Constant buffer sequence requirements">ConstBufferSequence</a><span class="special">,</span>
  36     <span class="keyword">typename</span> <span class="identifier">CompletionCondition</span><span class="special">&gt;</span>
  37 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">write_at</span><span class="special">(</span>
  38     <span class="identifier">SyncRandomAccessWriteDevice</span> <span class="special">&amp;</span> <span class="identifier">d</span><span class="special">,</span>
  39     <span class="identifier">uint64_t</span> <span class="identifier">offset</span><span class="special">,</span>
  40     <span class="keyword">const</span> <span class="identifier">ConstBufferSequence</span> <span class="special">&amp;</span> <span class="identifier">buffers</span><span class="special">,</span>
  41     <span class="identifier">CompletionCondition</span> <span class="identifier">completion_condition</span><span class="special">);</span>
  42 </pre>
  43 <p>
  44           This function is used to write a certain number of bytes of data to a random
  45           access device at a specified offset. The call will block until one of the
  46           following conditions is true:
  47         </p>
  48 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  49 <li class="listitem">
  50               All of the data in the supplied buffers has been written. That is,
  51               the bytes transferred is equal to the sum of the buffer sizes.
  52             </li>
  53 <li class="listitem">
  54               The completion_condition function object returns 0.
  55             </li>
  56 </ul></div>
  57 <p>
  58           This operation is implemented in terms of zero or more calls to the device's
  59           write_some_at function.
  60         </p>
  61 <h6>
  62 <a name="boost_asio.reference.write_at.overload3.h0"></a>
  63           <span class="phrase"><a name="boost_asio.reference.write_at.overload3.parameters"></a></span><a class="link" href="overload3.html#boost_asio.reference.write_at.overload3.parameters">Parameters</a>
  64         </h6>
  65 <div class="variablelist">
  66 <p class="title"><b></b></p>
  67 <dl class="variablelist">
  68 <dt><span class="term">d</span></dt>
  69 <dd><p>
  70                 The device to which the data is to be written. The type must support
  71                 the SyncRandomAccessWriteDevice concept.
  72               </p></dd>
  73 <dt><span class="term">offset</span></dt>
  74 <dd><p>
  75                 The offset at which the data will be written.
  76               </p></dd>
  77 <dt><span class="term">buffers</span></dt>
  78 <dd><p>
  79                 One or more buffers containing the data to be written. The sum of
  80                 the buffer sizes indicates the maximum number of bytes to write to
  81                 the device.
  82               </p></dd>
  83 <dt><span class="term">completion_condition</span></dt>
  84 <dd>
  85 <p>
  86                 The function object to be called to determine whether the write operation
  87                 is complete. The signature of the function object must be:
  88 </p>
  89 <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>
  90   <span class="comment">// Result of latest write_some_at operation.</span>
  91   <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>
  92
  93   <span class="comment">// Number of bytes transferred so far.</span>
  94   <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
  95 <span class="special">);</span>
  96 </pre>
  97 <p>
  98                 A return value of 0 indicates that the write operation is complete.
  99                 A non-zero return value indicates the maximum number of bytes to
 100                 be written on the next call to the device's write_some_at function.
 101               </p>
 102 </dd>
 103 </dl>
 104 </div>
 105 <h6>
 106 <a name="boost_asio.reference.write_at.overload3.h1"></a>
 107           <span class="phrase"><a name="boost_asio.reference.write_at.overload3.return_value"></a></span><a class="link" href="overload3.html#boost_asio.reference.write_at.overload3.return_value">Return Value</a>
 108         </h6>
 109 <p>
 110           The number of bytes transferred.
 111         </p>
 112 <h6>
 113 <a name="boost_asio.reference.write_at.overload3.h2"></a>
 114           <span class="phrase"><a name="boost_asio.reference.write_at.overload3.exceptions"></a></span><a class="link" href="overload3.html#boost_asio.reference.write_at.overload3.exceptions">Exceptions</a>
 115         </h6>
 116 <div class="variablelist">
 117 <p class="title"><b></b></p>
 118 <dl class="variablelist">
 119 <dt><span class="term">boost::system::system_error</span></dt>
 120 <dd><p>
 121                 Thrown on failure.
 122               </p></dd>
 123 </dl>
 124 </div>
 125 <h6>
 126 <a name="boost_asio.reference.write_at.overload3.h3"></a>
 127           <span class="phrase"><a name="boost_asio.reference.write_at.overload3.example"></a></span><a class="link" href="overload3.html#boost_asio.reference.write_at.overload3.example">Example</a>
 128         </h6>
 129 <p>
 130           To write 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:
 131         </p>
 132 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">write_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>
 133     <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>
 134 </pre>
 135 <p>
 136           See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span class="identifier">buffer</span></code></a>
 137           documentation for information on writing multiple buffers in one go, and
 138           how to use it with arrays, boost::array or std::vector.
 139         </p>
 140 </div>
 141 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 142 <td align="left"></td>
 143 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2017 Christopher M. Kohlhoff<p>
 144         Distributed under the Boost Software License, Version 1.0. (See accompanying
 145         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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