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169 lines
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<title>read_until (21 of 24 overloads)</title>
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<div class="titlepage"><div><div><h4 class="title">
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<a name="boost_asio.reference.read_until.overload21"></a><a class="link" href="overload21.html" title="read_until (21 of 24 overloads)">read_until
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(21 of 24 overloads)</a>
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</h4></div></div></div>
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<p>
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Read data into a dynamic buffer sequence until some part of the data it
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contains matches a regular expression.
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</p>
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<pre class="programlisting">template<
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typename <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a>,
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typename <a class="link" href="../DynamicBuffer_v2.html" title="Dynamic buffer requirements (version 2)">DynamicBuffer_v2</a>>
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std::size_t read_until(
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SyncReadStream & s,
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DynamicBuffer_v2 buffers,
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const boost::regex & expr,
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typename constraint< is_dynamic_buffer_v2< DynamicBuffer_v2 >::value >::type = 0);
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</pre>
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<p>
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This function is used to read data into the specified dynamic buffer sequence
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until the dynamic buffer sequence's get area contains some data that matches
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a regular expression. The call will block until one of the following conditions
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is true:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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A substring of the dynamic buffer sequence's get area matches the regular
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expression.
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</li>
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<li class="listitem">
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An error occurred.
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</li>
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</ul></div>
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<p>
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This operation is implemented in terms of zero or more calls to the stream's
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read_some function. If the dynamic buffer sequence's get area already contains
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data that matches the regular expression, the function returns immediately.
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</p>
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<h6>
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<a name="boost_asio.reference.read_until.overload21.h0"></a>
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<span class="phrase"><a name="boost_asio.reference.read_until.overload21.parameters"></a></span><a class="link" href="overload21.html#boost_asio.reference.read_until.overload21.parameters">Parameters</a>
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</h6>
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<div class="variablelist">
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<p class="title"><b></b></p>
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<dl class="variablelist">
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<dt><span class="term">s</span></dt>
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<dd><p>
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The stream from which the data is to be read. The type must support
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the SyncReadStream concept.
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</p></dd>
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<dt><span class="term">buffers</span></dt>
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<dd><p>
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A dynamic buffer sequence into which the data will be read.
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</p></dd>
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<dt><span class="term">expr</span></dt>
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<dd><p>
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The regular expression.
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</p></dd>
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</dl>
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</div>
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<h6>
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<a name="boost_asio.reference.read_until.overload21.h1"></a>
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<span class="phrase"><a name="boost_asio.reference.read_until.overload21.return_value"></a></span><a class="link" href="overload21.html#boost_asio.reference.read_until.overload21.return_value">Return
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Value</a>
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</h6>
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<p>
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The number of bytes in the dynamic buffer sequence's get area up to and
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including the substring that matches the regular expression.
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</p>
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<h6>
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<a name="boost_asio.reference.read_until.overload21.h2"></a>
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<span class="phrase"><a name="boost_asio.reference.read_until.overload21.exceptions"></a></span><a class="link" href="overload21.html#boost_asio.reference.read_until.overload21.exceptions">Exceptions</a>
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</h6>
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<div class="variablelist">
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<p class="title"><b></b></p>
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<dl class="variablelist">
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<dt><span class="term">boost::system::system_error</span></dt>
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<dd><p>
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Thrown on failure.
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</p></dd>
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</dl>
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</div>
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<h6>
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<a name="boost_asio.reference.read_until.overload21.h3"></a>
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<span class="phrase"><a name="boost_asio.reference.read_until.overload21.remarks"></a></span><a class="link" href="overload21.html#boost_asio.reference.read_until.overload21.remarks">Remarks</a>
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</h6>
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<p>
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After a successful read_until operation, the dynamic buffer sequence may
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contain additional data beyond that which matched the regular expression.
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An application will typically leave that data in the dynamic buffer sequence
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for a subsequent read_until operation to examine.
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</p>
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<h6>
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<a name="boost_asio.reference.read_until.overload21.h4"></a>
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<span class="phrase"><a name="boost_asio.reference.read_until.overload21.example"></a></span><a class="link" href="overload21.html#boost_asio.reference.read_until.overload21.example">Example</a>
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</h6>
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<p>
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To read data into a <code class="computeroutput">std::string</code> until a CR-LF sequence is
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encountered:
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</p>
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<pre class="programlisting">std::string data;
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std::size_t n = boost::asio::read_until(s,
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boost::asio::dynamic_buffer(data), boost::regex("\r\n"));
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std::string line = data.substr(0, n);
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data.erase(0, n);
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</pre>
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<p>
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After the <code class="computeroutput">read_until</code> operation completes successfully, the
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string <code class="computeroutput">data</code> contains the delimiter:
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</p>
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<pre class="programlisting">{ 'a', 'b', ..., 'c', '\r', '\n', 'd', 'e', ... }
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</pre>
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<p>
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The call to <code class="computeroutput">substr</code> then extracts the data up to and including
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the delimiter, so that the string <code class="computeroutput">line</code> contains:
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</p>
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<pre class="programlisting">{ 'a', 'b', ..., 'c', '\r', '\n' }
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</pre>
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<p>
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After the call to <code class="computeroutput">erase</code>, the remaining data is left in the
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buffer <code class="computeroutput">b</code> as follows:
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</p>
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<pre class="programlisting">{ 'd', 'e', ... }
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</pre>
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<p>
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This data may be the start of a new line, to be extracted by a subsequent
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<code class="computeroutput">read_until</code> operation.
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</p>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 Christopher
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M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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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</p>
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</div></td>
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