<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>async_read_until (4 of 4 overloads)</title> <link rel="stylesheet" href="../../../boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2"> <link rel="start" href="../../../index.html" title="Asio"> <link rel="up" href="../async_read_until.html" title="async_read_until"> <link rel="prev" href="overload3.html" title="async_read_until (3 of 4 overloads)"> <link rel="next" href="../async_write.html" title="async_write"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../../asio.png"></td></tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="overload3.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../async_read_until.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="../async_write.html"><img src="../../../next.png" alt="Next"></a> </div> <div class="section" lang="en"> <div class="titlepage"><div><div><h4 class="title"> <a name="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> <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="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">boost</span><span class="special">::</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="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 type="disc"> <li> The match condition function object returns a std::pair where the second element evaluates to true. </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 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> <a name="asio.reference.async_read_until.overload4.parameters"></a><h6> <a name="id590092"></a> <a class="link" href="overload4.html#asio.reference.async_read_until.overload4.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. </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">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 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">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.overload4.remarks"></a><h6> <a name="id590498"></a> <a class="link" href="overload4.html#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> <a name="asio.reference.async_read_until.overload4.examples"></a><h6> <a name="id590550"></a> <a class="link" href="overload4.html#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">asio</span><span class="special">::</span><span class="identifier">buffers_iterator</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">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="identifier">asio</span><span class="special">::</span><span class="identifier">streambuf</span> <span class="identifier">b</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">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="identifier">asio</span><span class="special">::</span><span class="identifier">streambuf</span> <span class="identifier">b</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 - 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> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="overload3.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../async_read_until.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="../async_write.html"><img src="../../../next.png" alt="Next"></a> </div> </body> </html>