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<title>async_read_until (5 of 8 overloads)</title>
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<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.async_read_until.overload5"></a><a class="link" href="overload5.html" title="async_read_until (5 of 8 overloads)">async_read_until
(5 of 8 overloads)</a>
</h4></div></div></div>
<p>
Start an asynchronous operation to read data into a streambuf until it
contains a specified delimiter.
</p>
<pre class="programlisting">template<
typename <a class="link" href="../AsyncReadStream.html" title="Buffer-oriented asynchronous read stream requirements">AsyncReadStream</a>,
typename Allocator,
typename <a class="link" href="../ReadHandler.html" title="Read handler requirements">ReadHandler</a>>
<a class="link" href="../asynchronous_operations/automatic_deduction_of_initiating_function_return_type.html" title="Automatic deduction of initiating function return type"><span class="emphasis"><em>DEDUCED</em></span></a> async_read_until(
AsyncReadStream & s,
boost::asio::basic_streambuf< Allocator > & b,
char delim,
ReadHandler && handler);
</pre>
<p>
This function is used to asynchronously read data into the specified streambuf
until the streambuf's get area contains the specified delimiter. The function
call always returns immediately. The asynchronous operation will continue
until one of the following conditions is true:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
The get area of the streambuf contains the specified delimiter.
</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
async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
If the streambuf's get area already contains the delimiter, 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>
<h6>
<a name="boost_asio.reference.async_read_until.overload5.h0"></a>
<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>
</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 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">delim</span></dt>
<dd><p>
The delimiter character.
</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">void handler(
// Result of operation.
const boost::system::error_code& error,
// The number of bytes in the streambuf's get
// area up to and including the delimiter.
// 0 if an error occurred.
std::size_t bytes_transferred
);
</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">boost::asio::io_context::post()</code>.
</p>
</dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.async_read_until.overload5.h1"></a>
<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>
</h6>
<p>
After a successful async_read_until operation, the streambuf may contain
additional data beyond the delimiter. An application will typically leave
that data in the streambuf for a subsequent async_read_until operation
to examine.
</p>
<h6>
<a name="boost_asio.reference.async_read_until.overload5.h2"></a>
<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>
</h6>
<p>
To asynchronously read data into a streambuf until a newline is encountered:
</p>
<pre class="programlisting">boost::asio::streambuf b;
...
void handler(const boost::system::error_code& e, std::size_t size)
{
if (!e)
{
std::istream is(&b);
std::string line;
std::getline(is, line);
...
}
}
...
boost::asio::async_read_until(s, b, '\n', handler);
</pre>
<p>
After the <code class="computeroutput">async_read_until</code> operation completes successfully,
the buffer <code class="computeroutput">b</code> contains the delimiter:
</p>
<pre class="programlisting">{ 'a', 'b', ..., 'c', '\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' }
</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">async_read_until</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 © 2003-2018 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>
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