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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.async_read.overload7"></a><a class="link" href="overload7.html" title="async_read (7 of 8 overloads)">async_read
  28         (7 of 8 overloads)</a>
  29 </h4></div></div></div>
  30 <p>
  31           Start an asynchronous operation to read a certain amount of data from a
  32           stream.
  33         </p>
  34 <pre class="programlisting">template&lt;
  35     typename <a class="link" href="../AsyncReadStream.html" title="Buffer-oriented asynchronous read stream requirements">AsyncReadStream</a>,
  36     typename <a class="link" href="../DynamicBuffer_v2.html" title="Dynamic buffer requirements (version 2)">DynamicBuffer_v2</a>,
  37     typename <a class="link" href="../ReadHandler.html" title="Read handler requirements">ReadHandler</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_read(
  39     AsyncReadStream &amp; s,
  40     DynamicBuffer_v2 buffers,
  41     ReadHandler &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>,
  42     typename enable_if&lt; is_dynamic_buffer_v2&lt; DynamicBuffer_v2 &gt;::value &gt;::type *  = 0);
  43 </pre>
  44 <p>
  45           This function is used to asynchronously read a certain number of bytes
  46           of data from a stream. The function call always returns immediately. The
  47           asynchronous operation will continue until one of the following conditions
  48           is true:
  49         </p>
  50 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  51 <li class="listitem">
  52               The specified dynamic buffer sequence is full (that is, it has reached
  53               maximum size).
  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 stream's
  61           async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
  62           The program must ensure that the stream performs no other read operations
  63           (such as async_read, the stream's async_read_some function, or any other
  64           composed operations that perform reads) until this operation completes.
  65         </p>
  66 <h6>
  67 <a name="boost_asio.reference.async_read.overload7.h0"></a>
  68           <span class="phrase"><a name="boost_asio.reference.async_read.overload7.parameters"></a></span><a class="link" href="overload7.html#boost_asio.reference.async_read.overload7.parameters">Parameters</a>
  69         </h6>
  70 <div class="variablelist">
  71 <p class="title"><b></b></p>
  72 <dl class="variablelist">
  73 <dt><span class="term">s</span></dt>
  74 <dd><p>
  75                 The stream from which the data is to be read. The type must support
  76                 the AsyncReadStream concept.
  77               </p></dd>
  78 <dt><span class="term">buffers</span></dt>
  79 <dd><p>
  80                 The dynamic buffer sequence into which the data will be read. Although
  81                 the buffers object may be copied as necessary, ownership of the underlying
  82                 memory blocks is retained by the caller, which must guarantee that
  83                 they remain valid until the handler is called.
  84               </p></dd>
  85 <dt><span class="term">handler</span></dt>
  86 <dd>
  87 <p>
  88                 The handler to be called when the read operation completes. Copies
  89                 will be made of the handler as required. The function signature of
  90                 the handler must be:
  91 </p>
  92 <pre class="programlisting">void handler(
  93   const boost::system::error_code&amp; error, // Result of operation.
  94
  95   std::size_t bytes_transferred           // Number of bytes copied into the
  96                                           // buffers. If an error occurred,
  97                                           // this will be the  number of
  98                                           // bytes successfully transferred
  99                                           // prior to the error.
 100 );
 101 </pre>
 102 <p>
 103                 Regardless of whether the asynchronous operation completes immediately
 104                 or not, the handler will not be invoked from within this function.
 105                 On immediate completion, invocation of the handler will be performed
 106                 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>.
 107               </p>
 108 </dd>
 109 </dl>
 110 </div>
 111 <h6>
 112 <a name="boost_asio.reference.async_read.overload7.h1"></a>
 113           <span class="phrase"><a name="boost_asio.reference.async_read.overload7.remarks"></a></span><a class="link" href="overload7.html#boost_asio.reference.async_read.overload7.remarks">Remarks</a>
 114         </h6>
 115 <p>
 116           This overload is equivalent to calling:
 117         </p>
 118 <pre class="programlisting">boost::asio::async_read(
 119     s, buffers,
 120     boost::asio::transfer_all(),
 121     handler);
 122 </pre>
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 126 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2019 Christopher M. Kohlhoff<p>
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