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<title>async_read_until (2 of 12 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.overload2"></a><a class="link" href="overload2.html" title="async_read_until (2 of 12 overloads)">async_read_until
(2 of 12 overloads)</a>
</h4></div></div></div>
<p>
Start an asynchronous operation to read data into a dynamic buffer sequence
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 <a class="link" href="../DynamicBuffer_v1.html" title="Dynamic buffer requirements (version 1)">DynamicBuffer_v1</a>,
typename <a class="link" href="../ReadHandler.html" title="Read handler requirements">ReadHandler</a>>
<a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_read_until(
AsyncReadStream & s,
DynamicBuffer_v1 && buffers,
string_view delim,
ReadHandler && handler,
typename enable_if< is_dynamic_buffer_v1< typename decay< DynamicBuffer_v1 >::type >::value &&!is_dynamic_buffer_v2< typename decay< DynamicBuffer_v1 >::type >::value >::type * = 0);
</pre>
<p>
This function is used to asynchronously read data into the specified dynamic
buffer sequence until the dynamic buffer sequence'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 dynamic buffer sequence 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 dynamic buffer sequence'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.overload2.h0"></a>
<span class="phrase"><a name="boost_asio.reference.async_read_until.overload2.parameters"></a></span><a class="link" href="overload2.html#boost_asio.reference.async_read_until.overload2.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">buffers</span></dt>
<dd><p>
The dynamic buffer sequence into which the data will be read. Although
the buffers object may be copied as necessary, ownership of the underlying
memory blocks is retained by the caller, which must guarantee that
they remain valid until the handler is called.
</p></dd>
<dt><span class="term">delim</span></dt>
<dd><p>
The delimiter string.
</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 dynamic buffer sequence'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.
On immediate completion, invocation of the handler will be performed
in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>.
</p>
</dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.async_read_until.overload2.h1"></a>
<span class="phrase"><a name="boost_asio.reference.async_read_until.overload2.remarks"></a></span><a class="link" href="overload2.html#boost_asio.reference.async_read_until.overload2.remarks">Remarks</a>
</h6>
<p>
After a successful async_read_until operation, the dynamic buffer sequence
may contain additional data beyond the delimiter. An application will typically
leave that data in the dynamic buffer sequence for a subsequent async_read_until
operation to examine.
</p>
<h6>
<a name="boost_asio.reference.async_read_until.overload2.h2"></a>
<span class="phrase"><a name="boost_asio.reference.async_read_until.overload2.example"></a></span><a class="link" href="overload2.html#boost_asio.reference.async_read_until.overload2.example">Example</a>
</h6>
<p>
To asynchronously read data into a <code class="computeroutput">std::string</code> until a CR-LF
sequence is encountered:
</p>
<pre class="programlisting">std::string data;
...
void handler(const boost::system::error_code& e, std::size_t size)
{
if (!e)
{
std::string line = data.substr(0, n);
data.erase(0, n);
...
}
}
...
boost::asio::async_read_until(s, data, "\r\n", handler);
</pre>
<p>
After the <code class="computeroutput">async_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
string <code class="computeroutput">data</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 © 2003-2019 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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