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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.async_read_until.overload1"></a><a class="link" href="overload1.html" title="async_read_until (1 of 12 overloads)">async_read_until
  28         (1 of 12 overloads)</a>
  29 </h4></div></div></div>
  30 <p>
  31           Start an asynchronous operation to read data into a dynamic buffer sequence
  32           until it contains a specified delimiter.
  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_v1.html" title="Dynamic buffer requirements (version 1)">DynamicBuffer_v1</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_until(
  39     AsyncReadStream &amp; s,
  40     DynamicBuffer_v1 &amp;&amp; buffers,
  41     char delim,
  42     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>,
  43     typename enable_if&lt; is_dynamic_buffer_v1&lt; typename decay&lt; DynamicBuffer_v1 &gt;::type &gt;::value &amp;&amp;!is_dynamic_buffer_v2&lt; typename decay&lt; DynamicBuffer_v1 &gt;::type &gt;::value &gt;::type *  = 0);
  44 </pre>
  45 <p>
  46           This function is used to asynchronously read data into the specified dynamic
  47           buffer sequence until the dynamic buffer sequence's get area contains the
  48           specified delimiter. The function call always returns immediately. The
  49           asynchronous operation will continue until one of the following conditions
  50           is true:
  51         </p>
  52 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  53 <li class="listitem">
  54               The get area of the dynamic buffer sequence contains the specified
  55               delimiter.
  56             </li>
  57 <li class="listitem">
  58               An error occurred.
  59             </li>
  60 </ul></div>
  61 <p>
  62           This operation is implemented in terms of zero or more calls to the stream's
  63           async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
  64           If the dynamic buffer sequence's get area already contains the delimiter,
  65           this asynchronous operation completes immediately. The program must ensure
  66           that the stream performs no other read operations (such as async_read,
  67           async_read_until, the stream's async_read_some function, or any other composed
  68           operations that perform reads) until this operation completes.
  69         </p>
  70 <h6>
  71 <a name="boost_asio.reference.async_read_until.overload1.h0"></a>
  72           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload1.parameters"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_read_until.overload1.parameters">Parameters</a>
  73         </h6>
  74 <div class="variablelist">
  75 <p class="title"><b></b></p>
  76 <dl class="variablelist">
  77 <dt><span class="term">s</span></dt>
  78 <dd><p>
  79                 The stream from which the data is to be read. The type must support
  80                 the AsyncReadStream concept.
  81               </p></dd>
  82 <dt><span class="term">buffers</span></dt>
  83 <dd><p>
  84                 The dynamic buffer sequence into which the data will be read. Although
  85                 the buffers object may be copied as necessary, ownership of the underlying
  86                 memory blocks is retained by the caller, which must guarantee that
  87                 they remain valid until the handler is called.
  88               </p></dd>
  89 <dt><span class="term">delim</span></dt>
  90 <dd><p>
  91                 The delimiter character.
  92               </p></dd>
  93 <dt><span class="term">handler</span></dt>
  94 <dd>
  95 <p>
  96                 The handler to be called when the read operation completes. Copies
  97                 will be made of the handler as required. The function signature of
  98                 the handler must be:
  99 </p>
 100 <pre class="programlisting">void handler(
 101   // Result of operation.
 102   const boost::system::error_code&amp; error,
 103
 104   // The number of bytes in the dynamic buffer sequence's
 105   // get area up to and including the delimiter.
 106   // 0 if an error occurred.
 107   std::size_t bytes_transferred
 108 );
 109 </pre>
 110 <p>
 111                 Regardless of whether the asynchronous operation completes immediately
 112                 or not, the handler will not be invoked from within this function.
 113                 On immediate completion, invocation of the handler will be performed
 114                 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>.
 115               </p>
 116 </dd>
 117 </dl>
 118 </div>
 119 <h6>
 120 <a name="boost_asio.reference.async_read_until.overload1.h1"></a>
 121           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload1.remarks"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_read_until.overload1.remarks">Remarks</a>
 122         </h6>
 123 <p>
 124           After a successful async_read_until operation, the dynamic buffer sequence
 125           may contain additional data beyond the delimiter. An application will typically
 126           leave that data in the dynamic buffer sequence for a subsequent async_read_until
 127           operation to examine.
 128         </p>
 129 <h6>
 130 <a name="boost_asio.reference.async_read_until.overload1.h2"></a>
 131           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload1.example"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_read_until.overload1.example">Example</a>
 132         </h6>
 133 <p>
 134           To asynchronously read data into a <code class="computeroutput">std::string</code> until a newline
 135           is encountered:
 136         </p>
 137 <pre class="programlisting">std::string data;
 138 ...
 139 void handler(const boost::system::error_code&amp; e, std::size_t size)
 140 {
 141   if (!e)
 142   {
 143     std::string line = data.substr(0, n);
 144     data.erase(0, n);
 145     ...
 146   }
 147 }
 148 ...
 149 boost::asio::async_read_until(s, data, '\n', handler);
 150 </pre>
 151 <p>
 152           After the <code class="computeroutput">async_read_until</code> operation completes successfully,
 153           the buffer <code class="computeroutput">data</code> contains the delimiter:
 154         </p>
 155 <pre class="programlisting">{ 'a', 'b', ..., 'c', '\n', 'd', 'e', ... }
 156 </pre>
 157 <p>
 158           The call to <code class="computeroutput">substr</code> then extracts the data up to and including
 159           the delimiter, so that the string <code class="computeroutput">line</code> contains:
 160         </p>
 161 <pre class="programlisting">{ 'a', 'b', ..., 'c', '\n' }
 162 </pre>
 163 <p>
 164           After the call to <code class="computeroutput">erase</code>, the remaining data is left in the
 165           buffer <code class="computeroutput">data</code> as follows:
 166         </p>
 167 <pre class="programlisting">{ 'd', 'e', ... }
 168 </pre>
 169 <p>
 170           This data may be the start of a new line, to be extracted by a subsequent
 171           <code class="computeroutput">async_read_until</code> operation.
 172         </p>
 173 </div>
 174 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 175 <td align="left"></td>
 176 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2019 Christopher M. Kohlhoff<p>
 177         Distributed under the Boost Software License, Version 1.0. (See accompanying
 178         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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