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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.async_read_until.overload7"></a><a class="link" href="overload7.html" title="async_read_until (7 of 12 overloads)">async_read_until
  28         (7 of 12 overloads)</a>
  29 </h4></div></div></div>
  30 <p>
  31           Start an asynchronous operation to read data into a streambuf until some
  32           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 Allocator,
  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     boost::asio::basic_streambuf&lt; Allocator &gt; &amp; b,
  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 </pre>
  44 <p>
  45           This function is used to asynchronously read data into the specified streambuf
  46           until the streambuf's get area contains some data that matches a regular
  47           expression. The function call always returns immediately. The asynchronous
  48           operation will continue until one of the following conditions is true:
  49         </p>
  50 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  51 <li class="listitem">
  52               A substring of the streambuf's get area matches the regular expression.
  53             </li>
  54 <li class="listitem">
  55               An error occurred.
  56             </li>
  57 </ul></div>
  58 <p>
  59           This operation is implemented in terms of zero or more calls to the stream's
  60           async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
  61           If the streambuf's get area already contains data that matches the regular
  62           expression, this asynchronous operation completes immediately. The program
  63           must ensure that the stream performs no other read operations (such as
  64           async_read, async_read_until, the stream's async_read_some function, or
  65           any other composed operations that perform reads) until this operation
  66           completes.
  67         </p>
  68 <h6>
  69 <a name="boost_asio.reference.async_read_until.overload7.h0"></a>
  70           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload7.parameters"></a></span><a class="link" href="overload7.html#boost_asio.reference.async_read_until.overload7.parameters">Parameters</a>
  71         </h6>
  72 <div class="variablelist">
  73 <p class="title"><b></b></p>
  74 <dl class="variablelist">
  75 <dt><span class="term">s</span></dt>
  76 <dd><p>
  77                 The stream from which the data is to be read. The type must support
  78                 the AsyncReadStream concept.
  79               </p></dd>
  80 <dt><span class="term">b</span></dt>
  81 <dd><p>
  82                 A streambuf object into which the data will be read. Ownership of
  83                 the streambuf is retained by the caller, which must guarantee that
  84                 it remains valid until the handler is called.
  85               </p></dd>
  86 <dt><span class="term">expr</span></dt>
  87 <dd><p>
  88                 The regular expression.
  89               </p></dd>
  90 <dt><span class="term">handler</span></dt>
  91 <dd>
  92 <p>
  93                 The handler to be called when the read operation completes. Copies
  94                 will be made of the handler as required. The function signature of
  95                 the handler must be:
  96 </p>
  97 <pre class="programlisting">void handler(
  98   // Result of operation.
  99   const boost::system::error_code&amp; error,
 100
 101   // The number of bytes in the streambuf's get
 102   // area up to and including the substring
 103   // that matches the regular. expression.
 104   // 0 if an error occurred.
 105   std::size_t bytes_transferred
 106 );
 107 </pre>
 108 <p>
 109                 Regardless of whether the asynchronous operation completes immediately
 110                 or not, the handler will not be invoked from within this function.
 111                 On immediate completion, invocation of the handler will be performed
 112                 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>.
 113               </p>
 114 </dd>
 115 </dl>
 116 </div>
 117 <h6>
 118 <a name="boost_asio.reference.async_read_until.overload7.h1"></a>
 119           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload7.remarks"></a></span><a class="link" href="overload7.html#boost_asio.reference.async_read_until.overload7.remarks">Remarks</a>
 120         </h6>
 121 <p>
 122           After a successful async_read_until operation, the streambuf may contain
 123           additional data beyond that which matched the regular expression. An application
 124           will typically leave that data in the streambuf for a subsequent async_read_until
 125           operation to examine.
 126         </p>
 127 <h6>
 128 <a name="boost_asio.reference.async_read_until.overload7.h2"></a>
 129           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload7.example"></a></span><a class="link" href="overload7.html#boost_asio.reference.async_read_until.overload7.example">Example</a>
 130         </h6>
 131 <p>
 132           To asynchronously read data into a streambuf until a CR-LF sequence is
 133           encountered:
 134         </p>
 135 <pre class="programlisting">boost::asio::streambuf b;
 136 ...
 137 void handler(const boost::system::error_code&amp; e, std::size_t size)
 138 {
 139   if (!e)
 140   {
 141     std::istream is(&amp;b);
 142     std::string line;
 143     std::getline(is, line);
 144     ...
 145   }
 146 }
 147 ...
 148 boost::asio::async_read_until(s, b, boost::regex("\r\n"), handler);
 149 </pre>
 150 <p>
 151           After the <code class="computeroutput">async_read_until</code> operation completes successfully,
 152           the buffer <code class="computeroutput">b</code> contains the data which matched the regular expression:
 153         </p>
 154 <pre class="programlisting">{ 'a', 'b', ..., 'c', '\r', '\n', 'd', 'e', ... }
 155 </pre>
 156 <p>
 157           The call to <code class="computeroutput">std::getline</code> then extracts the data up to and
 158           including the newline (which is discarded), so that the string <code class="computeroutput">line</code>
 159           contains:
 160         </p>
 161 <pre class="programlisting">{ 'a', 'b', ..., 'c', '\r' }
 162 </pre>
 163 <p>
 164           The remaining data is left in the buffer <code class="computeroutput">b</code> as follows:
 165         </p>
 166 <pre class="programlisting">{ 'd', 'e', ... }
 167 </pre>
 168 <p>
 169           This data may be the start of a new line, to be extracted by a subsequent
 170           <code class="computeroutput">async_read_until</code> operation.
 171         </p>
 172 </div>
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 174 <td align="left"></td>
 175 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2019 Christopher M. Kohlhoff<p>
 176         Distributed under the Boost Software License, Version 1.0. (See accompanying
 177         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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