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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.async_read_until.overload3"></a><a class="link" href="overload3.html" title="async_read_until (3 of 12 overloads)">async_read_until
  28         (3 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 some part of its data matches a regular expression.
  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     const boost::regex &amp; expr,
  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 some
  48           data that matches a regular expression. The function call always returns
  49           immediately. The asynchronous operation will continue until one of the
  50           following conditions is true:
  51         </p>
  52 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  53 <li class="listitem">
  54               A substring of the dynamic buffer sequence's get area matches the regular
  55               expression.
  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 data that matches
  65           the regular expression, this asynchronous operation completes immediately.
  66           The program must ensure that the stream performs no other read operations
  67           (such as async_read, async_read_until, the stream's async_read_some function,
  68           or any other composed operations that perform reads) until this operation
  69           completes.
  70         </p>
  71 <h6>
  72 <a name="boost_asio.reference.async_read_until.overload3.h0"></a>
  73           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload3.parameters"></a></span><a class="link" href="overload3.html#boost_asio.reference.async_read_until.overload3.parameters">Parameters</a>
  74         </h6>
  75 <div class="variablelist">
  76 <p class="title"><b></b></p>
  77 <dl class="variablelist">
  78 <dt><span class="term">s</span></dt>
  79 <dd><p>
  80                 The stream from which the data is to be read. The type must support
  81                 the AsyncReadStream concept.
  82               </p></dd>
  83 <dt><span class="term">buffers</span></dt>
  84 <dd><p>
  85                 The dynamic buffer sequence into which the data will be read. Although
  86                 the buffers object may be copied as necessary, ownership of the underlying
  87                 memory blocks is retained by the caller, which must guarantee that
  88                 they remain valid until the handler is called.
  89               </p></dd>
  90 <dt><span class="term">expr</span></dt>
  91 <dd><p>
  92                 The regular expression.
  93               </p></dd>
  94 <dt><span class="term">handler</span></dt>
  95 <dd>
  96 <p>
  97                 The handler to be called when the read operation completes. Copies
  98                 will be made of the handler as required. The function signature of
  99                 the handler must be:
 100 </p>
 101 <pre class="programlisting">void handler(
 102   // Result of operation.
 103   const boost::system::error_code&amp; error,
 104
 105   // The number of bytes in the dynamic buffer
 106   // sequence's get area up to and including the
 107   // substring that matches the regular expression.
 108   // 0 if an error occurred.
 109   std::size_t bytes_transferred
 110 );
 111 </pre>
 112 <p>
 113                 Regardless of whether the asynchronous operation completes immediately
 114                 or not, the handler will not be invoked from within this function.
 115                 On immediate completion, invocation of the handler will be performed
 116                 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>.
 117               </p>
 118 </dd>
 119 </dl>
 120 </div>
 121 <h6>
 122 <a name="boost_asio.reference.async_read_until.overload3.h1"></a>
 123           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload3.remarks"></a></span><a class="link" href="overload3.html#boost_asio.reference.async_read_until.overload3.remarks">Remarks</a>
 124         </h6>
 125 <p>
 126           After a successful async_read_until operation, the dynamic buffer sequence
 127           may contain additional data beyond that which matched the regular expression.
 128           An application will typically leave that data in the dynamic buffer sequence
 129           for a subsequent async_read_until operation to examine.
 130         </p>
 131 <h6>
 132 <a name="boost_asio.reference.async_read_until.overload3.h2"></a>
 133           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload3.example"></a></span><a class="link" href="overload3.html#boost_asio.reference.async_read_until.overload3.example">Example</a>
 134         </h6>
 135 <p>
 136           To asynchronously read data into a <code class="computeroutput">std::string</code> until a CR-LF
 137           sequence is encountered:
 138         </p>
 139 <pre class="programlisting">std::string data;
 140 ...
 141 void handler(const boost::system::error_code&amp; e, std::size_t size)
 142 {
 143   if (!e)
 144   {
 145     std::string line = data.substr(0, n);
 146     data.erase(0, n);
 147     ...
 148   }
 149 }
 150 ...
 151 boost::asio::async_read_until(s, data,
 152     boost::regex("\r\n"), handler);
 153 </pre>
 154 <p>
 155           After the <code class="computeroutput">async_read_until</code> operation completes successfully,
 156           the string <code class="computeroutput">data</code> contains the data which matched the regular
 157           expression:
 158         </p>
 159 <pre class="programlisting">{ 'a', 'b', ..., 'c', '\r', '\n', 'd', 'e', ... }
 160 </pre>
 161 <p>
 162           The call to <code class="computeroutput">substr</code> then extracts the data up to and including
 163           the match, so that the string <code class="computeroutput">line</code> contains:
 164         </p>
 165 <pre class="programlisting">{ 'a', 'b', ..., 'c', '\r', '\n' }
 166 </pre>
 167 <p>
 168           After the call to <code class="computeroutput">erase</code>, the remaining data is left in the
 169           string <code class="computeroutput">data</code> as follows:
 170         </p>
 171 <pre class="programlisting">{ 'd', 'e', ... }
 172 </pre>
 173 <p>
 174           This data may be the start of a new line, to be extracted by a subsequent
 175           <code class="computeroutput">async_read_until</code> operation.
 176         </p>
 177 </div>
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 179 <td align="left"></td>
 180 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2019 Christopher M. Kohlhoff<p>
 181         Distributed under the Boost Software License, Version 1.0. (See accompanying
 182         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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