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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.async_read_until.overload3"></a><a class="link" href="overload3.html" title="async_read_until (3 of 4 overloads)">async_read_until
(3 of 4 overloads)</a>
</h4></div></div></div>
<p>
Start an asynchronous operation to read data into a streambuf until some
part of its data matches a regular expression.
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <a class="link" href="../AsyncReadStream.html" title="Buffer-oriented asynchronous read stream requirements">AsyncReadStream</a><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../ReadHandler.html" title="Read handler requirements">ReadHandler</a><span class="special">></span>
<span class="keyword">void</span> <span class="identifier">async_read_until</span><span class="special">(</span>
<span class="identifier">AsyncReadStream</span> <span class="special">&</span> <span class="identifier">s</span><span class="special">,</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">basic_streambuf</span><span class="special"><</span> <span class="identifier">Allocator</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">b</span><span class="special">,</span>
<span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">regex</span> <span class="special">&</span> <span class="identifier">expr</span><span class="special">,</span>
<span class="identifier">ReadHandler</span> <span class="identifier">handler</span><span class="special">);</span>
</pre>
<p>
This function is used to asynchronously read data into the specified streambuf
until the streambuf's get area contains some data that matches a regular
expression. The function call always returns immediately. The asynchronous
operation will continue until one of the following conditions is true:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
A substring of the streambuf's get area matches the regular expression.
</li>
<li>
An error occurred.
</li>
</ul></div>
<p>
This operation is implemented in terms of zero or more calls to the stream's
async_read_some function, and is known as a <span class="bold"><strong>composed
operation</strong></span>. If the streambuf's get area already contains data
that matches the regular expression, this asynchronous operation completes
immediately. The program must ensure that the stream performs no other
read operations (such as async_read, async_read_until, the stream's async_read_some
function, or any other composed operations that perform reads) until this
operation completes.
</p>
<a name="asio.reference.async_read_until.overload3.parameters"></a><h6>
<a name="id733752"></a>
<a class="link" href="overload3.html#asio.reference.async_read_until.overload3.parameters">Parameters</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">s</span></dt>
<dd><p>
The stream from which the data is to be read. The type must support
the AsyncReadStream concept.
</p></dd>
<dt><span class="term">b</span></dt>
<dd><p>
A streambuf object into which the data will be read. Ownership of
the streambuf is retained by the caller, which must guarantee that
it remains valid until the handler is called.
</p></dd>
<dt><span class="term">expr</span></dt>
<dd><p>
The regular expression.
</p></dd>
<dt><span class="term">handler</span></dt>
<dd>
<p>
The handler to be called when the read operation completes. Copies
will be made of the handler as required. The function signature of
the handler must be:
</p>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span>
<span class="comment">// Result of operation.
</span> <span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">error</span><span class="special">,</span>
<span class="comment">// The number of bytes in the streambuf's get
</span> <span class="comment">// area up to and including the substring
</span> <span class="comment">// that matches the regular. expression.
</span> <span class="comment">// 0 if an error occurred.
</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
<span class="special">);</span>
</pre>
<p>
Regardless of whether the asynchronous operation completes immediately
or not, the handler will not be invoked from within this function.
Invocation of the handler will be performed in a manner equivalent
to using <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">post</span><span class="special">()</span></code>.
</p>
</dd>
</dl>
</div>
<a name="asio.reference.async_read_until.overload3.remarks"></a><h6>
<a name="id733983"></a>
<a class="link" href="overload3.html#asio.reference.async_read_until.overload3.remarks">Remarks</a>
</h6>
<p>
After a successful async_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 async_read_until
operation to examine.
</p>
<a name="asio.reference.async_read_until.overload3.example"></a><h6>
<a name="id734009"></a>
<a class="link" href="overload3.html#asio.reference.async_read_until.overload3.example">Example</a>
</h6>
<p>
To asynchronously read data into a streambuf until a CR-LF sequence is
encountered:
</p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">streambuf</span> <span class="identifier">b</span><span class="special">;</span>
<span class="special">...</span>
<span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">e</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">size</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">if</span> <span class="special">(!</span><span class="identifier">e</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">istream</span> <span class="identifier">is</span><span class="special">(&</span><span class="identifier">b</span><span class="special">);</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">line</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">getline</span><span class="special">(</span><span class="identifier">is</span><span class="special">,</span> <span class="identifier">line</span><span class="special">);</span>
<span class="special">...</span>
<span class="special">}</span>
<span class="special">}</span>
<span class="special">...</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_read_until</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">b</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">regex</span><span class="special">(</span><span class="string">"\r\n"</span><span class="special">),</span> <span class="identifier">handler</span><span class="special">);</span>
</pre>
<p>
After the <code class="computeroutput"><span class="identifier">async_read_until</span></code>
operation completes successfully, the buffer <code class="computeroutput"><span class="identifier">b</span></code>
contains the data which matched the regular expression:
</p>
<pre class="programlisting"><span class="special">{</span> <span class="char">'a'</span><span class="special">,</span> <span class="char">'b'</span><span class="special">,</span> <span class="special">...,</span> <span class="char">'c'</span><span class="special">,</span> <span class="char">'\r'</span><span class="special">,</span> <span class="char">'\n'</span><span class="special">,</span> <span class="char">'d'</span><span class="special">,</span> <span class="char">'e'</span><span class="special">,</span> <span class="special">...</span> <span class="special">}</span>
</pre>
<p>
The call to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">getline</span></code> then extracts the data up to
and including the match, so that the string <code class="computeroutput"><span class="identifier">line</span></code>
contains:
</p>
<pre class="programlisting"><span class="special">{</span> <span class="char">'a'</span><span class="special">,</span> <span class="char">'b'</span><span class="special">,</span> <span class="special">...,</span> <span class="char">'c'</span><span class="special">,</span> <span class="char">'\r'</span><span class="special">,</span> <span class="char">'\n'</span> <span class="special">}</span>
</pre>
<p>
The remaining data is left in the buffer <code class="computeroutput"><span class="identifier">b</span></code>
as follows:
</p>
<pre class="programlisting"><span class="special">{</span> <span class="char">'d'</span><span class="special">,</span> <span class="char">'e'</span><span class="special">,</span> <span class="special">...</span> <span class="special">}</span>
</pre>
<p>
This data may be the start of a new line, to be extracted by a subsequent
<code class="computeroutput"><span class="identifier">async_read_until</span></code> operation.
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003 - 2010 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>)
</p>
</div></td>
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