1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>read_until (15 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="overload14.html" title="read_until (14 of 24 overloads)"> 10<link rel="next" href="overload16.html" title="read_until (16 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="overload14.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="overload16.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.overload15"></a><a class="link" href="overload15.html" title="read_until (15 of 24 overloads)">read_until 28 (15 of 24 overloads)</a> 29</h4></div></div></div> 30<p> 31 Read data into a streambuf until a function object indicates a match. 32 </p> 33<pre class="programlisting">template< 34 typename <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a>, 35 typename Allocator, 36 typename MatchCondition> 37std::size_t read_until( 38 SyncReadStream & s, 39 boost::asio::basic_streambuf< Allocator > & b, 40 MatchCondition match_condition, 41 typename enable_if< is_match_condition< MatchCondition >::value >::type * = 0); 42</pre> 43<p> 44 This function is used to read data into the specified streambuf until a 45 user-defined match condition function object, when applied to the data 46 contained in the streambuf, indicates a successful match. The call will 47 block until one of the following conditions is true: 48 </p> 49<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 50<li class="listitem"> 51 The match condition function object returns a std::pair where the second 52 element evaluates to true. 53 </li> 54<li class="listitem"> 55 An error occurred. 56 </li> 57</ul></div> 58<p> 59 This operation is implemented in terms of zero or more calls to the stream's 60 read_some function. If the match condition function object already indicates 61 a match, the function returns immediately. 62 </p> 63<h6> 64<a name="boost_asio.reference.read_until.overload15.h0"></a> 65 <span class="phrase"><a name="boost_asio.reference.read_until.overload15.parameters"></a></span><a class="link" href="overload15.html#boost_asio.reference.read_until.overload15.parameters">Parameters</a> 66 </h6> 67<div class="variablelist"> 68<p class="title"><b></b></p> 69<dl class="variablelist"> 70<dt><span class="term">s</span></dt> 71<dd><p> 72 The stream from which the data is to be read. The type must support 73 the SyncReadStream concept. 74 </p></dd> 75<dt><span class="term">b</span></dt> 76<dd><p> 77 A streambuf object into which the data will be read. 78 </p></dd> 79<dt><span class="term">match_condition</span></dt> 80<dd> 81<p> 82 The function object to be called to determine whether a match exists. 83 The signature of the function object must be: 84</p> 85<pre class="programlisting">pair<iterator, bool> match_condition(iterator begin, iterator end); 86</pre> 87<p> 88 where <code class="computeroutput">iterator</code> represents the type: 89</p> 90<pre class="programlisting">buffers_iterator<basic_streambuf<Allocator>::const_buffers_type> 91</pre> 92<p> 93 The iterator parameters <code class="computeroutput">begin</code> and <code class="computeroutput">end</code> define 94 the range of bytes to be scanned to determine whether there is a 95 match. The <code class="computeroutput">first</code> member of the return value is an iterator 96 marking one-past-the-end of the bytes that have been consumed by 97 the match function. This iterator is used to calculate the <code class="computeroutput">begin</code> 98 parameter for any subsequent invocation of the match condition. The 99 <code class="computeroutput">second</code> member of the return value is true if a match 100 has been found, false otherwise. 101 </p> 102</dd> 103</dl> 104</div> 105<h6> 106<a name="boost_asio.reference.read_until.overload15.h1"></a> 107 <span class="phrase"><a name="boost_asio.reference.read_until.overload15.return_value"></a></span><a class="link" href="overload15.html#boost_asio.reference.read_until.overload15.return_value">Return 108 Value</a> 109 </h6> 110<p> 111 The number of bytes in the streambuf's get area that have been fully consumed 112 by the match function. 113 </p> 114<h6> 115<a name="boost_asio.reference.read_until.overload15.h2"></a> 116 <span class="phrase"><a name="boost_asio.reference.read_until.overload15.exceptions"></a></span><a class="link" href="overload15.html#boost_asio.reference.read_until.overload15.exceptions">Exceptions</a> 117 </h6> 118<div class="variablelist"> 119<p class="title"><b></b></p> 120<dl class="variablelist"> 121<dt><span class="term">boost::system::system_error</span></dt> 122<dd><p> 123 Thrown on failure. 124 </p></dd> 125</dl> 126</div> 127<h6> 128<a name="boost_asio.reference.read_until.overload15.h3"></a> 129 <span class="phrase"><a name="boost_asio.reference.read_until.overload15.remarks"></a></span><a class="link" href="overload15.html#boost_asio.reference.read_until.overload15.remarks">Remarks</a> 130 </h6> 131<p> 132 After a successful read_until operation, the streambuf may contain additional 133 data beyond that which matched the function object. An application will 134 typically leave that data in the streambuf for a subsequent read_until 135 operation to examine. 136 </p> 137<p> 138 The default implementation of the <code class="computeroutput">is_match_condition</code> type 139 trait evaluates to true for function pointers and function objects with 140 a <code class="computeroutput">result_type</code> typedef. It must be specialised for other user-defined 141 function objects. 142 </p> 143<h6> 144<a name="boost_asio.reference.read_until.overload15.h4"></a> 145 <span class="phrase"><a name="boost_asio.reference.read_until.overload15.examples"></a></span><a class="link" href="overload15.html#boost_asio.reference.read_until.overload15.examples">Examples</a> 146 </h6> 147<p> 148 To read data into a streambuf until whitespace is encountered: 149 </p> 150<pre class="programlisting">typedef boost::asio::buffers_iterator< 151 boost::asio::streambuf::const_buffers_type> iterator; 152 153std::pair<iterator, bool> 154match_whitespace(iterator begin, iterator end) 155{ 156 iterator i = begin; 157 while (i != end) 158 if (std::isspace(*i++)) 159 return std::make_pair(i, true); 160 return std::make_pair(i, false); 161} 162... 163boost::asio::streambuf b; 164boost::asio::read_until(s, b, match_whitespace); 165</pre> 166<p> 167 To read data into a streambuf until a matching character is found: 168 </p> 169<pre class="programlisting">class match_char 170{ 171public: 172 explicit match_char(char c) : c_(c) {} 173 174 template <typename Iterator> 175 std::pair<Iterator, bool> operator()( 176 Iterator begin, Iterator end) const 177 { 178 Iterator i = begin; 179 while (i != end) 180 if (c_ == *i++) 181 return std::make_pair(i, true); 182 return std::make_pair(i, false); 183 } 184 185private: 186 char c_; 187}; 188 189namespace asio { 190 template <> struct is_match_condition<match_char> 191 : public boost::true_type {}; 192} // namespace asio 193... 194boost::asio::streambuf b; 195boost::asio::read_until(s, b, match_char('a')); 196</pre> 197</div> 198<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 199<td align="left"></td> 200<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 201 Kohlhoff<p> 202 Distributed under the Boost Software License, Version 1.0. (See accompanying 203 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>) 204 </p> 205</div></td> 206</tr></table> 207<hr> 208<div class="spirit-nav"> 209<a accesskey="p" href="overload14.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="overload16.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 210</div> 211</body> 212</html> 213
