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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"><span class="keyword">template</span><span class="special">&lt;</span>
  35     <span class="keyword">typename</span> <a class="link" href="../AsyncRandomAccessWriteDevice.html" title="Buffer-oriented asynchronous random-access write device requirements">AsyncRandomAccessWriteDevice</a><span class="special">,</span>
  36     <span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">,</span>
  37     <span class="keyword">typename</span> <a class="link" href="../WriteHandler.html" title="Write handler requirements">WriteHandler</a><span class="special">&gt;</span>
  38 <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.return_type_of_an_initiating_function"><span class="emphasis"><em>void-or-deduced</em></span></a> <span class="identifier">async_write_at</span><span class="special">(</span>
  39     <span class="identifier">AsyncRandomAccessWriteDevice</span> <span class="special">&amp;</span> <span class="identifier">d</span><span class="special">,</span>
  40     <span class="identifier">uint64_t</span> <span class="identifier">offset</span><span class="special">,</span>
  41     <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>
  42     <span class="identifier">WriteHandler</span> <span class="identifier">handler</span><span class="special">);</span>
  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"><span class="identifier">basic_streambuf</span></code></a> has been written.
  53             </li>
  54 <li class="listitem">
  55               An error occurred.
  56             </li>
  57 </ul></div>
  58 <p>
  59           This operation is implemented in terms of zero or more calls to the device's
  60           async_write_some_at function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
  61           The program must ensure that the device performs no <span class="emphasis"><em>overlapping</em></span>
  62           write operations (such as async_write_at, the device's async_write_some_at
  63           function, or any other composed operations that perform writes) until this
  64           operation completes. Operations are overlapping if the regions defined
  65           by their offsets, and the numbers of bytes to write, intersect.
  66         </p>
  67 <h6>
  68 <a name="boost_asio.reference.async_write_at.overload3.h0"></a>
  69           <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>
  70         </h6>
  71 <div class="variablelist">
  72 <p class="title"><b></b></p>
  73 <dl class="variablelist">
  74 <dt><span class="term">d</span></dt>
  75 <dd><p>
  76                 The device to which the data is to be written. The type must support
  77                 the AsyncRandomAccessWriteDevice concept.
  78               </p></dd>
  79 <dt><span class="term">offset</span></dt>
  80 <dd><p>
  81                 The offset at which the data will be written.
  82               </p></dd>
  83 <dt><span class="term">b</span></dt>
  84 <dd><p>
  85                 A <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput"><span class="identifier">basic_streambuf</span></code></a> object from
  86                 which data will be written. Ownership of the streambuf is retained
  87                 by the caller, which must guarantee that it remains valid until the
  88                 handler is called.
  89               </p></dd>
  90 <dt><span class="term">handler</span></dt>
  91 <dd>
  92 <p>
  93                 The handler to be called when the write operation completes. Copies
  94                 will be made of the handler as required. The function signature of
  95                 the handler must be:
  96 </p>
  97 <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span>
  98   <span class="comment">// Result of operation.</span>
  99   <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>
 100
 101   <span class="comment">// Number of bytes written from the buffers. If an error</span>
 102   <span class="comment">// occurred, this will be less than the sum of the buffer sizes.</span>
 103   <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
 104 <span class="special">);</span>
 105 </pre>
 106 <p>
 107                 Regardless of whether the asynchronous operation completes immediately
 108                 or not, the handler will not be invoked from within this function.
 109                 Invocation of the handler will be performed in a manner equivalent
 110                 to using <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">post</span><span class="special">()</span></code>.
 111               </p>
 112 </dd>
 113 </dl>
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