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<title>read_until (21 of 24 overloads)</title>
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<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.read_until.overload21"></a><a class="link" href="overload21.html" title="read_until (21 of 24 overloads)">read_until
(21 of 24 overloads)</a>
</h4></div></div></div>
<p>
Read data into a dynamic buffer sequence until some part of the data it
contains matches a regular expression.
</p>
<pre class="programlisting">template<
typename <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a>,
typename <a class="link" href="../DynamicBuffer_v2.html" title="Dynamic buffer requirements (version 2)">DynamicBuffer_v2</a>>
std::size_t read_until(
SyncReadStream & s,
DynamicBuffer_v2 buffers,
const boost::regex & expr,
typename enable_if< is_dynamic_buffer_v2< DynamicBuffer_v2 >::value >::type * = 0);
</pre>
<p>
This function is used to read data into the specified dynamic buffer sequence
until the dynamic buffer sequence's get area contains some data that matches
a regular expression. The call will block until one of the following conditions
is true:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
A substring of the dynamic buffer sequence's get area matches the regular
expression.
</li>
<li class="listitem">
An error occurred.
</li>
</ul></div>
<p>
This operation is implemented in terms of zero or more calls to the stream's
read_some function. If the dynamic buffer sequence's get area already contains
data that matches the regular expression, the function returns immediately.
</p>
<h6>
<a name="boost_asio.reference.read_until.overload21.h0"></a>
<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>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">s</span></dt>
<dd><p>
The stream from which the data is to be read. The type must support
the SyncReadStream concept.
</p></dd>
<dt><span class="term">buffers</span></dt>
<dd><p>
A dynamic buffer sequence into which the data will be read.
</p></dd>
<dt><span class="term">expr</span></dt>
<dd><p>
The regular expression.
</p></dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.read_until.overload21.h1"></a>
<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
Value</a>
</h6>
<p>
The number of bytes in the dynamic buffer sequence's get area up to and
including the substring that matches the regular expression.
</p>
<h6>
<a name="boost_asio.reference.read_until.overload21.h2"></a>
<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>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">boost::system::system_error</span></dt>
<dd><p>
Thrown on failure.
</p></dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.read_until.overload21.h3"></a>
<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>
</h6>
<p>
After a successful read_until operation, the dynamic buffer sequence may
contain additional data beyond that which matched the regular expression.
An application will typically leave that data in the dynamic buffer sequence
for a subsequent read_until operation to examine.
</p>
<h6>
<a name="boost_asio.reference.read_until.overload21.h4"></a>
<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>
</h6>
<p>
To read data into a <code class="computeroutput">std::string</code> until a CR-LF sequence is
encountered:
</p>
<pre class="programlisting">std::string data;
std::string n = boost::asio::read_until(s,
boost::asio::dynamic_buffer(data), boost::regex("\r\n"));
std::string line = data.substr(0, n);
data.erase(0, n);
</pre>
<p>
After the <code class="computeroutput">read_until</code> operation completes successfully, the
string <code class="computeroutput">data</code> contains the delimiter:
</p>
<pre class="programlisting">{ 'a', 'b', ..., 'c', '\r', '\n', 'd', 'e', ... }
</pre>
<p>
The call to <code class="computeroutput">substr</code> then extracts the data up to and including
the delimiter, so that the string <code class="computeroutput">line</code> contains:
</p>
<pre class="programlisting">{ 'a', 'b', ..., 'c', '\r', '\n' }
</pre>
<p>
After the call to <code class="computeroutput">erase</code>, the remaining data is left in the
buffer <code class="computeroutput">b</code> as follows:
</p>
<pre class="programlisting">{ 'd', 'e', ... }
</pre>
<p>
This data may be the start of a new line, to be extracted by a subsequent
<code class="computeroutput">read_until</code> operation.
</p>
</div>
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<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003-2019 Christopher M. Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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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