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<title>read_until (13 of 24 overloads)</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.read_until.overload13"></a><a class="link" href="overload13.html" title="read_until (13 of 24 overloads)">read_until
(13 of 24 overloads)</a>
</h4></div></div></div>
<p>
Read data into a streambuf until some part of the data it contains matches
a regular expression.
</p>
<pre class="programlisting">template&lt;
typename <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a>,
typename Allocator&gt;
std::size_t read_until(
SyncReadStream &amp; s,
boost::asio::basic_streambuf&lt; Allocator &gt; &amp; b,
const boost::regex &amp; expr);
</pre>
<p>
This function is used to read data into the specified streambuf until the
streambuf'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 streambuf'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 streambuf's get area already contains data that
matches the regular expression, the function returns immediately.
</p>
<h6>
<a name="boost_asio.reference.read_until.overload13.h0"></a>
<span class="phrase"><a name="boost_asio.reference.read_until.overload13.parameters"></a></span><a class="link" href="overload13.html#boost_asio.reference.read_until.overload13.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">b</span></dt>
<dd><p>
A streambuf object 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.overload13.h1"></a>
<span class="phrase"><a name="boost_asio.reference.read_until.overload13.return_value"></a></span><a class="link" href="overload13.html#boost_asio.reference.read_until.overload13.return_value">Return
Value</a>
</h6>
<p>
The number of bytes in the streambuf's get area up to and including the
substring that matches the regular expression.
</p>
<h6>
<a name="boost_asio.reference.read_until.overload13.h2"></a>
<span class="phrase"><a name="boost_asio.reference.read_until.overload13.exceptions"></a></span><a class="link" href="overload13.html#boost_asio.reference.read_until.overload13.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.overload13.h3"></a>
<span class="phrase"><a name="boost_asio.reference.read_until.overload13.remarks"></a></span><a class="link" href="overload13.html#boost_asio.reference.read_until.overload13.remarks">Remarks</a>
</h6>
<p>
After a successful read_until operation, the streambuf may contain additional
data beyond that which matched the regular expression. An application will
typically leave that data in the streambuf for a subsequent read_until
operation to examine.
</p>
<h6>
<a name="boost_asio.reference.read_until.overload13.h4"></a>
<span class="phrase"><a name="boost_asio.reference.read_until.overload13.example"></a></span><a class="link" href="overload13.html#boost_asio.reference.read_until.overload13.example">Example</a>
</h6>
<p>
To read data into a streambuf until a CR-LF sequence is encountered:
</p>
<pre class="programlisting">boost::asio::streambuf b;
boost::asio::read_until(s, b, boost::regex("\r\n"));
std::istream is(&amp;b);
std::string line;
std::getline(is, line);
</pre>
<p>
After the <code class="computeroutput">read_until</code> operation completes successfully, the
buffer <code class="computeroutput">b</code> contains the data which matched the regular expression:
</p>
<pre class="programlisting">{ 'a', 'b', ..., 'c', '\r', '\n', 'd', 'e', ... }
</pre>
<p>
The call to <code class="computeroutput">std::getline</code> then extracts the data up to and
including the newline (which is discarded), so that the string <code class="computeroutput">line</code>
contains:
</p>
<pre class="programlisting">{ 'a', 'b', ..., 'c', '\r' }
</pre>
<p>
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>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 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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