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<title>async_read_until (4 of 4 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.overload4"></a><a class="link" href="overload4.html" title="async_read_until (4 of 4 overloads)">async_read_until
(4 of 4 overloads)</a>
</h4></div></div></div>
<p>
Start an asynchronous operation to read data into a streambuf until a function
object indicates a match.
</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> <span class="identifier">MatchCondition</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>
<a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.return_type_of_an_initiating_function"><span class="emphasis"><em>void-or-deduced</em></span></a> <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">boost</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="identifier">MatchCondition</span> <span class="identifier">match_condition</span><span class="special">,</span>
<span class="identifier">ReadHandler</span> <span class="identifier">handler</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">enable_if</span><span class="special"><</span> <span class="identifier">is_match_condition</span><span class="special"><</span> <span class="identifier">MatchCondition</span> <span class="special">>::</span><span class="identifier">value</span> <span class="special">>::</span><span class="identifier">type</span> <span class="special">*</span> <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
</pre>
<p>
This function is used to asynchronously read data into the specified streambuf
until a user-defined match condition function object, when applied to the
data contained in the streambuf, indicates a successful match. 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 match condition function object returns a std::pair where the second
element evaluates to true.
</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 match condition function object already indicates a match, 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.overload4.h0"></a>
<span class="phrase"><a name="boost_asio.reference.async_read_until.overload4.parameters"></a></span><a class="link" href="overload4.html#boost_asio.reference.async_read_until.overload4.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.
</p></dd>
<dt><span class="term">match_condition</span></dt>
<dd>
<p>
The function object to be called to determine whether a match exists.
The signature of the function object must be:
</p>
<pre class="programlisting"><span class="identifier">pair</span><span class="special"><</span><span class="identifier">iterator</span><span class="special">,</span> <span class="keyword">bool</span><span class="special">></span> <span class="identifier">match_condition</span><span class="special">(</span><span class="identifier">iterator</span> <span class="identifier">begin</span><span class="special">,</span> <span class="identifier">iterator</span> <span class="identifier">end</span><span class="special">);</span>
</pre>
<p>
where <code class="computeroutput"><span class="identifier">iterator</span></code> represents
the type:
</p>
<pre class="programlisting"><span class="identifier">buffers_iterator</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="identifier">const_buffers_type</span><span class="special">></span>
</pre>
<p>
The iterator parameters <code class="computeroutput"><span class="identifier">begin</span></code>
and <code class="computeroutput"><span class="identifier">end</span></code> define the
range of bytes to be scanned to determine whether there is a match.
The <code class="computeroutput"><span class="identifier">first</span></code> member
of the return value is an iterator marking one-past-the-end of the
bytes that have been consumed by the match function. This iterator
is used to calculate the <code class="computeroutput"><span class="identifier">begin</span></code>
parameter for any subsequent invocation of the match condition. The
<code class="computeroutput"><span class="identifier">second</span></code> member of
the return value is true if a match has been found, false otherwise.
</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">boost</span><span class="special">::</span><span class="identifier">system</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 that have been fully consumed by the</span>
<span class="comment">// match function. O 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">boost</span><span class="special">::</span><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>
<h6>
<a name="boost_asio.reference.async_read_until.overload4.h1"></a>
<span class="phrase"><a name="boost_asio.reference.async_read_until.overload4.remarks"></a></span><a class="link" href="overload4.html#boost_asio.reference.async_read_until.overload4.remarks">Remarks</a>
</h6>
<p>
After a successful async_read_until operation, the streambuf may contain
additional data beyond that which matched the function object. An application
will typically leave that data in the streambuf for a subsequent async_read_until
operation to examine.
</p>
<p>
The default implementation of the <code class="computeroutput"><span class="identifier">is_match_condition</span></code>
type trait evaluates to true for function pointers and function objects
with a <code class="computeroutput"><span class="identifier">result_type</span></code> typedef.
It must be specialised for other user-defined function objects.
</p>
<h6>
<a name="boost_asio.reference.async_read_until.overload4.h2"></a>
<span class="phrase"><a name="boost_asio.reference.async_read_until.overload4.examples"></a></span><a class="link" href="overload4.html#boost_asio.reference.async_read_until.overload4.examples">Examples</a>
</h6>
<p>
To asynchronously read data into a streambuf until whitespace is encountered:
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffers_iterator</span><span class="special"><</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">streambuf</span><span class="special">::</span><span class="identifier">const_buffers_type</span><span class="special">></span> <span class="identifier">iterator</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">iterator</span><span class="special">,</span> <span class="keyword">bool</span><span class="special">></span>
<span class="identifier">match_whitespace</span><span class="special">(</span><span class="identifier">iterator</span> <span class="identifier">begin</span><span class="special">,</span> <span class="identifier">iterator</span> <span class="identifier">end</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">iterator</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">begin</span><span class="special">;</span>
<span class="keyword">while</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">!=</span> <span class="identifier">end</span><span class="special">)</span>
<span class="keyword">if</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">isspace</span><span class="special">(*</span><span class="identifier">i</span><span class="special">++))</span>
<span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="keyword">true</span><span class="special">);</span>
<span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="keyword">false</span><span class="special">);</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">boost</span><span class="special">::</span><span class="identifier">system</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="identifier">boost</span><span class="special">::</span><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="identifier">boost</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">match_whitespace</span><span class="special">,</span> <span class="identifier">handler</span><span class="special">);</span>
</pre>
<p>
To asynchronously read data into a streambuf until a matching character
is found:
</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">match_char</span>
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="keyword">explicit</span> <span class="identifier">match_char</span><span class="special">(</span><span class="keyword">char</span> <span class="identifier">c</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">c_</span><span class="special">(</span><span class="identifier">c</span><span class="special">)</span> <span class="special">{}</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">></span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="keyword">bool</span><span class="special">></span> <span class="keyword">operator</span><span class="special">()(</span>
<span class="identifier">Iterator</span> <span class="identifier">begin</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="identifier">end</span><span class="special">)</span> <span class="keyword">const</span>
<span class="special">{</span>
<span class="identifier">Iterator</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">begin</span><span class="special">;</span>
<span class="keyword">while</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">!=</span> <span class="identifier">end</span><span class="special">)</span>
<span class="keyword">if</span> <span class="special">(</span><span class="identifier">c_</span> <span class="special">==</span> <span class="special">*</span><span class="identifier">i</span><span class="special">++)</span>
<span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="keyword">true</span><span class="special">);</span>
<span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="keyword">false</span><span class="special">);</span>
<span class="special">}</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="keyword">char</span> <span class="identifier">c_</span><span class="special">;</span>
<span class="special">};</span>
<span class="keyword">namespace</span> <span class="identifier">asio</span> <span class="special">{</span>
<span class="keyword">template</span> <span class="special"><></span> <span class="keyword">struct</span> <span class="identifier">is_match_condition</span><span class="special"><</span><span class="identifier">match_char</span><span class="special">></span>
<span class="special">:</span> <span class="keyword">public</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">true_type</span> <span class="special">{};</span>
<span class="special">}</span> <span class="comment">// namespace asio</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">boost</span><span class="special">::</span><span class="identifier">system</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="identifier">boost</span><span class="special">::</span><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="identifier">boost</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">match_char</span><span class="special">(</span><span class="char">'a'</span><span class="special">),</span> <span class="identifier">handler</span><span class="special">);</span>
</pre>
</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 © 2003-2014 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>
</tr></table>
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