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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.async_write.overload2"></a><a class="link" href="overload2.html" title="async_write (2 of 4 overloads)">async_write
  28         (2 of 4 overloads)</a>
  29 </h4></div></div></div>
  30 <p>
  31           Start an asynchronous operation to write a certain amount of data to a
  32           stream.
  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="../AsyncWriteStream.html" title="Buffer-oriented asynchronous write stream requirements">AsyncWriteStream</a><span class="special">,</span>
  36     <span class="keyword">typename</span> <a class="link" href="../ConstBufferSequence.html" title="Constant buffer sequence requirements">ConstBufferSequence</a><span class="special">,</span>
  37     <span class="keyword">typename</span> <span class="identifier">CompletionCondition</span><span class="special">,</span>
  38     <span class="keyword">typename</span> <a class="link" href="../WriteHandler.html" title="Write handler requirements">WriteHandler</a><span class="special">&gt;</span>
  39 <span class="keyword">void</span> <span class="identifier">async_write</span><span class="special">(</span>
  40     <span class="identifier">AsyncWriteStream</span> <span class="special">&amp;</span> <span class="identifier">s</span><span class="special">,</span>
  41     <span class="keyword">const</span> <span class="identifier">ConstBufferSequence</span> <span class="special">&amp;</span> <span class="identifier">buffers</span><span class="special">,</span>
  42     <span class="identifier">CompletionCondition</span> <span class="identifier">completion_condition</span><span class="special">,</span>
  43     <span class="identifier">WriteHandler</span> <span class="identifier">handler</span><span class="special">);</span>
  44 </pre>
  45 <p>
  46           This function is used to asynchronously write a certain number of bytes
  47           of data to a stream. The function call always returns immediately. The
  48           asynchronous operation will continue until one of the following conditions
  49           is true:
  50         </p>
  51 <div class="itemizedlist"><ul class="itemizedlist" type="disc">
  52 <li class="listitem">
  53               All of the data in the supplied buffers has been written. That is,
  54               the bytes transferred is equal to the sum of the buffer sizes.
  55             </li>
  56 <li class="listitem">
  57               The completion_condition function object returns 0.
  58             </li>
  59 </ul></div>
  60 <p>
  61           This operation is implemented in terms of zero or more calls to the stream's
  62           async_write_some function, and is known as a <span class="bold"><strong>composed
  63           operation</strong></span>. The program must ensure that the stream performs
  64           no other write operations (such as async_write, the stream's async_write_some
  65           function, or any other composed operations that perform writes) until this
  66           operation completes.
  67         </p>
  68 <h6>
  69 <a name="boost_asio.reference.async_write.overload2.h0"></a>
  70           <span><a name="boost_asio.reference.async_write.overload2.parameters"></a></span><a class="link" href="overload2.html#boost_asio.reference.async_write.overload2.parameters">Parameters</a>
  71         </h6>
  72 <div class="variablelist">
  73 <p class="title"><b></b></p>
  74 <dl>
  75 <dt><span class="term">s</span></dt>
  76 <dd><p>
  77                 The stream to which the data is to be written. The type must support
  78                 the AsyncWriteStream concept.
  79               </p></dd>
  80 <dt><span class="term">buffers</span></dt>
  81 <dd><p>
  82                 One or more buffers containing the data to be written. Although the
  83                 buffers object may be copied as necessary, ownership of the underlying
  84                 memory blocks is retained by the caller, which must guarantee that
  85                 they remain valid until the handler is called.
  86               </p></dd>
  87 <dt><span class="term">completion_condition</span></dt>
  88 <dd>
  89 <p>
  90                 The function object to be called to determine whether the write operation
  91                 is complete. The signature of the function object must be:
  92 </p>
  93 <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>
  94   <span class="comment">// Result of latest async_write_some operation.</span>
  95   <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>
  96
  97   <span class="comment">// Number of bytes transferred so far.</span>
  98   <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
  99 <span class="special">);</span>
 100 </pre>
 101 <p>
 102                 A return value of 0 indicates that the write operation is complete.
 103                 A non-zero return value indicates the maximum number of bytes to
 104                 be written on the next call to the stream's async_write_some function.
 105               </p>
 106 </dd>
 107 <dt><span class="term">handler</span></dt>
 108 <dd>
 109 <p>
 110                 The handler to be called when the write operation completes. Copies
 111                 will be made of the handler as required. The function signature of
 112                 the handler must be:
 113 </p>
 114 <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span>
 115   <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> <span class="comment">// Result of operation.</span>
 116
 117   <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>           <span class="comment">// Number of bytes written from the</span>
 118                                           <span class="comment">// buffers. If an error occurred,</span>
 119                                           <span class="comment">// this will be less than the sum</span>
 120                                           <span class="comment">// of the buffer sizes.</span>
 121 <span class="special">);</span>
 122 </pre>
 123 <p>
 124                 Regardless of whether the asynchronous operation completes immediately
 125                 or not, the handler will not be invoked from within this function.
 126                 Invocation of the handler will be performed in a manner equivalent
 127                 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>.
 128               </p>
 129 </dd>
 130 </dl>
 131 </div>
 132 <h6>
 133 <a name="boost_asio.reference.async_write.overload2.h1"></a>
 134           <span><a name="boost_asio.reference.async_write.overload2.example"></a></span><a class="link" href="overload2.html#boost_asio.reference.async_write.overload2.example">Example</a>
 135         </h6>
 136 <p>
 137           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:
 138         </p>
 139 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span>
 140     <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>
 141     <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>
 142     <span class="identifier">handler</span><span class="special">);</span>
 143 </pre>
 144 <p>
 145           See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span class="identifier">buffer</span></code></a>
 146           documentation for information on writing multiple buffers in one go, and
 147           how to use it with arrays, boost::array or std::vector.
 148         </p>
 149 </div>
 150 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 151 <td align="left"></td>
 152 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2012 Christopher M. Kohlhoff<p>
 153         Distributed under the Boost Software License, Version 1.0. (See accompanying
 154         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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