1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>read_until (23 of 24 overloads)</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../boost_asio.html" title="Boost.Asio"> 8<link rel="up" href="../read_until.html" title="read_until"> 9<link rel="prev" href="overload22.html" title="read_until (22 of 24 overloads)"> 10<link rel="next" href="overload24.html" title="read_until (24 of 24 overloads)"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="overload22.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../read_until.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../boost_asio.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overload24.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="boost_asio.reference.read_until.overload23"></a><a class="link" href="overload23.html" title="read_until (23 of 24 overloads)">read_until 28 (23 of 24 overloads)</a> 29</h4></div></div></div> 30<p> 31 Read data into a dynamic buffer sequence until a function object indicates 32 a match. 33 </p> 34<pre class="programlisting">template< 35 typename <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a>, 36 typename <a class="link" href="../DynamicBuffer_v2.html" title="Dynamic buffer requirements (version 2)">DynamicBuffer_v2</a>, 37 typename MatchCondition> 38std::size_t read_until( 39 SyncReadStream & s, 40 DynamicBuffer_v2 buffers, 41 MatchCondition match_condition, 42 typename enable_if< is_match_condition< MatchCondition >::value &&is_dynamic_buffer_v2< DynamicBuffer_v2 >::value >::type * = 0); 43</pre> 44<p> 45 This function is used to read data into the specified dynamic buffer sequence 46 until a user-defined match condition function object, when applied to the 47 data contained in the dynamic buffer sequence, indicates a successful match. 48 The call will block until one of the following conditions is true: 49 </p> 50<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 51<li class="listitem"> 52 The match condition function object returns a std::pair where the second 53 element evaluates to true. 54 </li> 55<li class="listitem"> 56 An error occurred. 57 </li> 58</ul></div> 59<p> 60 This operation is implemented in terms of zero or more calls to the stream's 61 read_some function. If the match condition function object already indicates 62 a match, the function returns immediately. 63 </p> 64<h6> 65<a name="boost_asio.reference.read_until.overload23.h0"></a> 66 <span class="phrase"><a name="boost_asio.reference.read_until.overload23.parameters"></a></span><a class="link" href="overload23.html#boost_asio.reference.read_until.overload23.parameters">Parameters</a> 67 </h6> 68<div class="variablelist"> 69<p class="title"><b></b></p> 70<dl class="variablelist"> 71<dt><span class="term">s</span></dt> 72<dd><p> 73 The stream from which the data is to be read. The type must support 74 the SyncReadStream concept. 75 </p></dd> 76<dt><span class="term">buffers</span></dt> 77<dd><p> 78 A dynamic buffer sequence into which the data will be read. 79 </p></dd> 80<dt><span class="term">match_condition</span></dt> 81<dd> 82<p> 83 The function object to be called to determine whether a match exists. 84 The signature of the function object must be: 85</p> 86<pre class="programlisting">pair<iterator, bool> match_condition(iterator begin, iterator end); 87</pre> 88<p> 89 where <code class="computeroutput">iterator</code> represents the type: 90</p> 91<pre class="programlisting">buffers_iterator<typename DynamicBuffer_v2::const_buffers_type> 92</pre> 93<p> 94 The iterator parameters <code class="computeroutput">begin</code> and <code class="computeroutput">end</code> define 95 the range of bytes to be scanned to determine whether there is a 96 match. The <code class="computeroutput">first</code> member of the return value is an iterator 97 marking one-past-the-end of the bytes that have been consumed by 98 the match function. This iterator is used to calculate the <code class="computeroutput">begin</code> 99 parameter for any subsequent invocation of the match condition. The 100 <code class="computeroutput">second</code> member of the return value is true if a match 101 has been found, false otherwise. 102 </p> 103</dd> 104</dl> 105</div> 106<h6> 107<a name="boost_asio.reference.read_until.overload23.h1"></a> 108 <span class="phrase"><a name="boost_asio.reference.read_until.overload23.return_value"></a></span><a class="link" href="overload23.html#boost_asio.reference.read_until.overload23.return_value">Return 109 Value</a> 110 </h6> 111<p> 112 The number of bytes in the dynamic_buffer's get area that have been fully 113 consumed by the match function. 114 </p> 115<h6> 116<a name="boost_asio.reference.read_until.overload23.h2"></a> 117 <span class="phrase"><a name="boost_asio.reference.read_until.overload23.exceptions"></a></span><a class="link" href="overload23.html#boost_asio.reference.read_until.overload23.exceptions">Exceptions</a> 118 </h6> 119<div class="variablelist"> 120<p class="title"><b></b></p> 121<dl class="variablelist"> 122<dt><span class="term">boost::system::system_error</span></dt> 123<dd><p> 124 Thrown on failure. 125 </p></dd> 126</dl> 127</div> 128<h6> 129<a name="boost_asio.reference.read_until.overload23.h3"></a> 130 <span class="phrase"><a name="boost_asio.reference.read_until.overload23.remarks"></a></span><a class="link" href="overload23.html#boost_asio.reference.read_until.overload23.remarks">Remarks</a> 131 </h6> 132<p> 133 After a successful read_until operation, the dynamic buffer sequence may 134 contain additional data beyond that which matched the function object. 135 An application will typically leave that data in the dynamic buffer sequence 136 for a subsequent read_until operation to examine. 137 </p> 138<p> 139 The default implementation of the <code class="computeroutput">is_match_condition</code> type 140 trait evaluates to true for function pointers and function objects with 141 a <code class="computeroutput">result_type</code> typedef. It must be specialised for other user-defined 142 function objects. 143 </p> 144<h6> 145<a name="boost_asio.reference.read_until.overload23.h4"></a> 146 <span class="phrase"><a name="boost_asio.reference.read_until.overload23.examples"></a></span><a class="link" href="overload23.html#boost_asio.reference.read_until.overload23.examples">Examples</a> 147 </h6> 148<p> 149 To read data into a dynamic buffer sequence until whitespace is encountered: 150 </p> 151<pre class="programlisting">typedef boost::asio::buffers_iterator< 152 boost::asio::const_buffers_1> iterator; 153 154std::pair<iterator, bool> 155match_whitespace(iterator begin, iterator end) 156{ 157 iterator i = begin; 158 while (i != end) 159 if (std::isspace(*i++)) 160 return std::make_pair(i, true); 161 return std::make_pair(i, false); 162} 163... 164std::string data; 165boost::asio::read_until(s, data, match_whitespace); 166</pre> 167<p> 168 To read data into a <code class="computeroutput">std::string</code> until a matching character 169 is found: 170 </p> 171<pre class="programlisting">class match_char 172{ 173public: 174 explicit match_char(char c) : c_(c) {} 175 176 template <typename Iterator> 177 std::pair<Iterator, bool> operator()( 178 Iterator begin, Iterator end) const 179 { 180 Iterator i = begin; 181 while (i != end) 182 if (c_ == *i++) 183 return std::make_pair(i, true); 184 return std::make_pair(i, false); 185 } 186 187private: 188 char c_; 189}; 190 191namespace asio { 192 template <> struct is_match_condition<match_char> 193 : public boost::true_type {}; 194} // namespace asio 195... 196std::string data; 197boost::asio::read_until(s, data, match_char('a')); 198</pre> 199</div> 200<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 201<td align="left"></td> 202<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 203 Kohlhoff<p> 204 Distributed under the Boost Software License, Version 1.0. (See accompanying 205 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>) 206 </p> 207</div></td> 208</tr></table> 209<hr> 210<div class="spirit-nav"> 211<a accesskey="p" href="overload22.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../read_until.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../boost_asio.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overload24.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 212</div> 213</body> 214</html> 215
