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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.async_read_until.overload5"></a><a class="link" href="overload5.html" title="async_read_until (5 of 12 overloads)">async_read_until
  28         (5 of 12 overloads)</a>
  29 </h4></div></div></div>
  30 <p>
  31           Start an asynchronous operation to read data into a streambuf until it
  32           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 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     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 </pre>
  44 <p>
  45           This function is used to asynchronously read data into the specified streambuf
  46           until the streambuf's get area contains the specified delimiter. The function
  47           call always returns immediately. The asynchronous operation will continue
  48           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               The get area of the streambuf contains the specified delimiter.
  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 the delimiter, this asynchronous
  62           operation completes immediately. The program must ensure that the stream
  63           performs no other read operations (such as async_read, async_read_until,
  64           the stream's async_read_some function, or any other composed operations
  65           that perform reads) until this operation completes.
  66         </p>
  67 <h6>
  68 <a name="boost_asio.reference.async_read_until.overload5.h0"></a>
  69           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload5.parameters"></a></span><a class="link" href="overload5.html#boost_asio.reference.async_read_until.overload5.parameters">Parameters</a>
  70         </h6>
  71 <div class="variablelist">
  72 <p class="title"><b></b></p>
  73 <dl class="variablelist">
  74 <dt><span class="term">s</span></dt>
  75 <dd><p>
  76                 The stream from which the data is to be read. The type must support
  77                 the AsyncReadStream concept.
  78               </p></dd>
  79 <dt><span class="term">b</span></dt>
  80 <dd><p>
  81                 A streambuf object into which the data will be read. Ownership of
  82                 the streambuf is retained by the caller, which must guarantee that
  83                 it remains valid until the handler is called.
  84               </p></dd>
  85 <dt><span class="term">delim</span></dt>
  86 <dd><p>
  87                 The delimiter character.
  88               </p></dd>
  89 <dt><span class="term">handler</span></dt>
  90 <dd>
  91 <p>
  92                 The handler to be called when the read operation completes. Copies
  93                 will be made of the handler as required. The function signature of
  94                 the handler must be:
  95 </p>
  96 <pre class="programlisting">void handler(
  97   // Result of operation.
  98   const boost::system::error_code&amp; error,
  99
 100   // The number of bytes in the streambuf's get
 101   // area up to and including the delimiter.
 102   // 0 if an error occurred.
 103   std::size_t bytes_transferred
 104 );
 105 </pre>
 106 <p>
 107                 Regardless of whether the asynchronous operation completes immediately
 108                 or not, the handler will not be invoked from within this function.
 109                 On immediate completion, invocation of the handler will be performed
 110                 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>.
 111               </p>
 112 </dd>
 113 </dl>
 114 </div>
 115 <h6>
 116 <a name="boost_asio.reference.async_read_until.overload5.h1"></a>
 117           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload5.remarks"></a></span><a class="link" href="overload5.html#boost_asio.reference.async_read_until.overload5.remarks">Remarks</a>
 118         </h6>
 119 <p>
 120           After a successful async_read_until operation, the streambuf may contain
 121           additional data beyond the delimiter. An application will typically leave
 122           that data in the streambuf for a subsequent async_read_until operation
 123           to examine.
 124         </p>
 125 <h6>
 126 <a name="boost_asio.reference.async_read_until.overload5.h2"></a>
 127           <span class="phrase"><a name="boost_asio.reference.async_read_until.overload5.example"></a></span><a class="link" href="overload5.html#boost_asio.reference.async_read_until.overload5.example">Example</a>
 128         </h6>
 129 <p>
 130           To asynchronously read data into a streambuf until a newline is encountered:
 131         </p>
 132 <pre class="programlisting">boost::asio::streambuf b;
 133 ...
 134 void handler(const boost::system::error_code&amp; e, std::size_t size)
 135 {
 136   if (!e)
 137   {
 138     std::istream is(&amp;b);
 139     std::string line;
 140     std::getline(is, line);
 141     ...
 142   }
 143 }
 144 ...
 145 boost::asio::async_read_until(s, b, '\n', handler);
 146 </pre>
 147 <p>
 148           After the <code class="computeroutput">async_read_until</code> operation completes successfully,
 149           the buffer <code class="computeroutput">b</code> contains the delimiter:
 150         </p>
 151 <pre class="programlisting">{ 'a', 'b', ..., 'c', '\n', 'd', 'e', ... }
 152 </pre>
 153 <p>
 154           The call to <code class="computeroutput">std::getline</code> then extracts the data up to and
 155           including the newline (which is discarded), so that the string <code class="computeroutput">line</code>
 156           contains:
 157         </p>
 158 <pre class="programlisting">{ 'a', 'b', ..., 'c' }
 159 </pre>
 160 <p>
 161           The remaining data is left in the buffer <code class="computeroutput">b</code> as follows:
 162         </p>
 163 <pre class="programlisting">{ 'd', 'e', ... }
 164 </pre>
 165 <p>
 166           This data may be the start of a new line, to be extracted by a subsequent
 167           <code class="computeroutput">async_read_until</code> operation.
 168         </p>
 169 </div>
 170 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 171 <td align="left"></td>
 172 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2019 Christopher M. Kohlhoff<p>
 173         Distributed under the Boost Software License, Version 1.0. (See accompanying
 174         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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