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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.write_at.overload7"></a><a class="link" href="overload7.html" title="write_at (7 of 8 overloads)">write_at (7
  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> <span class="identifier">Allocator</span><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="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>
  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 <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput"><span class="identifier">basic_streambuf</span></code></a> has been written.
  51             </li>
  52 <li class="listitem">
  53               The completion_condition function object returns 0.
  54             </li>
  55 </ul></div>
  56 <p>
  57           This operation is implemented in terms of zero or more calls to the device's
  58           write_some_at function.
  59         </p>
  60 <h6>
  61 <a name="boost_asio.reference.write_at.overload7.h0"></a>
  62           <span class="phrase"><a name="boost_asio.reference.write_at.overload7.parameters"></a></span><a class="link" href="overload7.html#boost_asio.reference.write_at.overload7.parameters">Parameters</a>
  63         </h6>
  64 <div class="variablelist">
  65 <p class="title"><b></b></p>
  66 <dl class="variablelist">
  67 <dt><span class="term">d</span></dt>
  68 <dd><p>
  69                 The device to which the data is to be written. The type must support
  70                 the SyncRandomAccessWriteDevice concept.
  71               </p></dd>
  72 <dt><span class="term">offset</span></dt>
  73 <dd><p>
  74                 The offset at which the data will be written.
  75               </p></dd>
  76 <dt><span class="term">b</span></dt>
  77 <dd><p>
  78                 The <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput"><span class="identifier">basic_streambuf</span></code></a> object from
  79                 which data will be written.
  80               </p></dd>
  81 <dt><span class="term">completion_condition</span></dt>
  82 <dd>
  83 <p>
  84                 The function object to be called to determine whether the write operation
  85                 is complete. The signature of the function object must be:
  86 </p>
  87 <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>
  88   <span class="comment">// Result of latest write_some_at operation.</span>
  89   <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>
  90
  91   <span class="comment">// Number of bytes transferred so far.</span>
  92   <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
  93 <span class="special">);</span>
  94 </pre>
  95 <p>
  96                 A return value of 0 indicates that the write operation is complete.
  97                 A non-zero return value indicates the maximum number of bytes to
  98                 be written on the next call to the device's write_some_at function.
  99               </p>
 100 </dd>
 101 </dl>
 102 </div>
 103 <h6>
 104 <a name="boost_asio.reference.write_at.overload7.h1"></a>
 105           <span class="phrase"><a name="boost_asio.reference.write_at.overload7.return_value"></a></span><a class="link" href="overload7.html#boost_asio.reference.write_at.overload7.return_value">Return Value</a>
 106         </h6>
 107 <p>
 108           The number of bytes transferred.
 109         </p>
 110 <h6>
 111 <a name="boost_asio.reference.write_at.overload7.h2"></a>
 112           <span class="phrase"><a name="boost_asio.reference.write_at.overload7.exceptions"></a></span><a class="link" href="overload7.html#boost_asio.reference.write_at.overload7.exceptions">Exceptions</a>
 113         </h6>
 114 <div class="variablelist">
 115 <p class="title"><b></b></p>
 116 <dl class="variablelist">
 117 <dt><span class="term">boost::system::system_error</span></dt>
 118 <dd><p>
 119                 Thrown on failure.
 120               </p></dd>
 121 </dl>
 122 </div>
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