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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.async_write_at.overload3"></a><a class="link" href="overload3.html" title="async_write_at (3 of 4 overloads)">async_write_at
  28         (3 of 4 overloads)</a>
  29 </h4></div></div></div>
  30 <p>
  31           Start an asynchronous operation to write all of the supplied data at the
  32           specified offset.
  33         </p>
  34 <pre class="programlisting">template&lt;
  35     typename <a class="link" href="../AsyncRandomAccessWriteDevice.html" title="Buffer-oriented asynchronous random-access write device requirements">AsyncRandomAccessWriteDevice</a>,
  36     typename Allocator,
  37     typename <a class="link" href="../WriteHandler.html" title="Write handler requirements">WriteHandler</a> = <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>&gt;
  38 <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_write_at(
  39     AsyncRandomAccessWriteDevice &amp; d,
  40     uint64_t offset,
  41     basic_streambuf&lt; Allocator &gt; &amp; b,
  42     WriteHandler &amp;&amp; handler = <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>);
  43 </pre>
  44 <p>
  45           This function is used to asynchronously write a certain number of bytes
  46           of data to a random access device at a specified offset. The function call
  47           always returns immediately. The asynchronous operation will continue until
  48           one of the following conditions is true:
  49         </p>
  50 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  51 <li class="listitem">
  52               All of the data in the supplied <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput">basic_streambuf</code></a>
  53               has been written.
  54             </li>
  55 <li class="listitem">
  56               An error occurred.
  57             </li>
  58 </ul></div>
  59 <p>
  60           This operation is implemented in terms of zero or more calls to the device's
  61           async_write_some_at function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
  62           The program must ensure that the device performs no <span class="emphasis"><em>overlapping</em></span>
  63           write operations (such as async_write_at, the device's async_write_some_at
  64           function, or any other composed operations that perform writes) until this
  65           operation completes. Operations are overlapping if the regions defined
  66           by their offsets, and the numbers of bytes to write, intersect.
  67         </p>
  68 <h6>
  69 <a name="boost_asio.reference.async_write_at.overload3.h0"></a>
  70           <span class="phrase"><a name="boost_asio.reference.async_write_at.overload3.parameters"></a></span><a class="link" href="overload3.html#boost_asio.reference.async_write_at.overload3.parameters">Parameters</a>
  71         </h6>
  72 <div class="variablelist">
  73 <p class="title"><b></b></p>
  74 <dl class="variablelist">
  75 <dt><span class="term">d</span></dt>
  76 <dd><p>
  77                 The device to which the data is to be written. The type must support
  78                 the AsyncRandomAccessWriteDevice concept.
  79               </p></dd>
  80 <dt><span class="term">offset</span></dt>
  81 <dd><p>
  82                 The offset at which the data will be written.
  83               </p></dd>
  84 <dt><span class="term">b</span></dt>
  85 <dd><p>
  86                 A <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput">basic_streambuf</code></a>
  87                 object from which data will be written. Ownership of the streambuf
  88                 is retained by the caller, which must guarantee that it remains valid
  89                 until the handler is called.
  90               </p></dd>
  91 <dt><span class="term">handler</span></dt>
  92 <dd>
  93 <p>
  94                 The handler to be called when the write operation completes. Copies
  95                 will be made of the handler as required. The function signature of
  96                 the handler must be:
  97 </p>
  98 <pre class="programlisting">void handler(
  99   // Result of operation.
 100   const boost::system::error_code&amp; error,
 101
 102   // Number of bytes written from the buffers. If an error
 103   // occurred, this will be less than the sum of the buffer sizes.
 104   std::size_t bytes_transferred
 105 );
 106 </pre>
 107 <p>
 108                 Regardless of whether the asynchronous operation completes immediately
 109                 or not, the handler will not be invoked from within this function.
 110                 On immediate completion, invocation of the handler will be performed
 111                 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>.
 112               </p>
 113 </dd>
 114 </dl>
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