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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.async_read.overload1"></a><a class="link" href="overload1.html" title="async_read (1 of 8 overloads)">async_read
  28         (1 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="../MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</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     const MutableBufferSequence &amp; 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_mutable_buffer_sequence&lt; MutableBufferSequence &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 supplied buffers are full. That is, the bytes transferred is equal
  53               to the sum of the buffer sizes.
  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.overload1.h0"></a>
  68           <span class="phrase"><a name="boost_asio.reference.async_read.overload1.parameters"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_read.overload1.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                 One or more buffers into which the data will be read. The sum of
  81                 the buffer sizes indicates the maximum number of bytes to read from
  82                 the stream. Although the buffers object may be copied as necessary,
  83                 ownership of the underlying memory blocks is retained by the caller,
  84                 which must guarantee that they remain valid until the handler is
  85                 called.
  86               </p></dd>
  87 <dt><span class="term">handler</span></dt>
  88 <dd>
  89 <p>
  90                 The handler to be called when the read operation completes. Copies
  91                 will be made of the handler as required. The function signature of
  92                 the handler must be:
  93 </p>
  94 <pre class="programlisting">void handler(
  95   const boost::system::error_code&amp; error, // Result of operation.
  96
  97   std::size_t bytes_transferred           // Number of bytes copied into the
  98                                           // buffers. If an error occurred,
  99                                           // this will be the  number of
 100                                           // bytes successfully transferred
 101                                           // prior to the error.
 102 );
 103 </pre>
 104 <p>
 105                 Regardless of whether the asynchronous operation completes immediately
 106                 or not, the handler will not be invoked from within this function.
 107                 On immediate completion, invocation of the handler will be performed
 108                 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>.
 109               </p>
 110 </dd>
 111 </dl>
 112 </div>
 113 <h6>
 114 <a name="boost_asio.reference.async_read.overload1.h1"></a>
 115           <span class="phrase"><a name="boost_asio.reference.async_read.overload1.example"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_read.overload1.example">Example</a>
 116         </h6>
 117 <p>
 118           To read into a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a>
 119           function as follows:
 120         </p>
 121 <pre class="programlisting">boost::asio::async_read(s, boost::asio::buffer(data, size), handler);
 122 </pre>
 123 <p>
 124           See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a>
 125           documentation for information on reading into multiple buffers in one go,
 126           and how to use it with arrays, boost::array or std::vector.
 127         </p>
 128 <h6>
 129 <a name="boost_asio.reference.async_read.overload1.h2"></a>
 130           <span class="phrase"><a name="boost_asio.reference.async_read.overload1.remarks"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_read.overload1.remarks">Remarks</a>
 131         </h6>
 132 <p>
 133           This overload is equivalent to calling:
 134         </p>
 135 <pre class="programlisting">boost::asio::async_read(
 136     s, buffers,
 137     boost::asio::transfer_all(),
 138     handler);
 139 </pre>
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