<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>read_until (7 of 24 overloads)</title> <link rel="stylesheet" href="../../../boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../../../index.html" title="Asio"> <link rel="up" href="../read_until.html" title="read_until"> <link rel="prev" href="overload6.html" title="read_until (6 of 24 overloads)"> <link rel="next" href="overload8.html" title="read_until (8 of 24 overloads)"> </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="overload6.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../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="overload8.html"><img src="../../../next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h4 class="title"> <a name="asio.reference.read_until.overload7"></a><a class="link" href="overload7.html" title="read_until (7 of 24 overloads)">read_until (7 of 24 overloads)</a> </h4></div></div></div> <p> Read data into a dynamic buffer sequence until a function object indicates a match. </p> <pre class="programlisting">template< typename <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a>, typename <a class="link" href="../DynamicBuffer_v1.html" title="Dynamic buffer requirements (version 1)">DynamicBuffer_v1</a>, typename MatchCondition> std::size_t read_until( SyncReadStream & s, DynamicBuffer_v1 && buffers, MatchCondition match_condition, typename enable_if< is_match_condition< MatchCondition >::value &&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 read data into the specified dynamic buffer sequence until a user-defined match condition function object, when applied to the data contained in the dynamic buffer sequence, indicates a successful match. The call will block until one of the following conditions is true: </p> <div class="itemizedlist"><ul class="itemizedlist" 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 read_some function. If the match condition function object already indicates a match, the function returns immediately. </p> <h6> <a name="asio.reference.read_until.overload7.h0"></a> <span><a name="asio.reference.read_until.overload7.parameters"></a></span><a class="link" href="overload7.html#asio.reference.read_until.overload7.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 SyncReadStream concept. </p></dd> <dt><span class="term">buffers</span></dt> <dd><p> A dynamic buffer sequence 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">pair<iterator, bool> match_condition(iterator begin, iterator end); </pre> <p> where <code class="computeroutput">iterator</code> represents the type: </p> <pre class="programlisting">buffers_iterator<typename DynamicBuffer_v1::const_buffers_type> </pre> <p> The iterator parameters <code class="computeroutput">begin</code> and <code class="computeroutput">end</code> define the range of bytes to be scanned to determine whether there is a match. The <code class="computeroutput">first</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">begin</code> parameter for any subsequent invocation of the match condition. The <code class="computeroutput">second</code> member of the return value is true if a match has been found, false otherwise. </p> </dd> </dl> </div> <h6> <a name="asio.reference.read_until.overload7.h1"></a> <span><a name="asio.reference.read_until.overload7.return_value"></a></span><a class="link" href="overload7.html#asio.reference.read_until.overload7.return_value">Return Value</a> </h6> <p> The number of bytes in the dynamic_buffer's get area that have been fully consumed by the match function. </p> <h6> <a name="asio.reference.read_until.overload7.h2"></a> <span><a name="asio.reference.read_until.overload7.exceptions"></a></span><a class="link" href="overload7.html#asio.reference.read_until.overload7.exceptions">Exceptions</a> </h6> <div class="variablelist"> <p class="title"><b></b></p> <dl> <dt><span class="term">asio::system_error</span></dt> <dd><p> Thrown on failure. </p></dd> </dl> </div> <h6> <a name="asio.reference.read_until.overload7.h3"></a> <span><a name="asio.reference.read_until.overload7.remarks"></a></span><a class="link" href="overload7.html#asio.reference.read_until.overload7.remarks">Remarks</a> </h6> <p> After a successful read_until operation, the dynamic buffer sequence may contain additional data beyond that which matched the function object. An application will typically leave that data in the dynamic buffer sequence for a subsequent read_until operation to examine. </p> <p> The default implementation of the <code class="computeroutput">is_match_condition</code> type trait evaluates to true for function pointers and function objects with a <code class="computeroutput">result_type</code> typedef. It must be specialised for other user-defined function objects. </p> <h6> <a name="asio.reference.read_until.overload7.h4"></a> <span><a name="asio.reference.read_until.overload7.examples"></a></span><a class="link" href="overload7.html#asio.reference.read_until.overload7.examples">Examples</a> </h6> <p> To read data into a dynamic buffer sequence until whitespace is encountered: </p> <pre class="programlisting">typedef asio::buffers_iterator< asio::const_buffers_1> iterator; std::pair<iterator, bool> match_whitespace(iterator begin, iterator end) { iterator i = begin; while (i != end) if (std::isspace(*i++)) return std::make_pair(i, true); return std::make_pair(i, false); } ... std::string data; asio::read_until(s, data, match_whitespace); </pre> <p> To read data into a <code class="computeroutput">std::string</code> until a matching character is found: </p> <pre class="programlisting">class match_char { public: explicit match_char(char c) : c_(c) {} template <typename Iterator> std::pair<Iterator, bool> operator()( Iterator begin, Iterator end) const { Iterator i = begin; while (i != end) if (c_ == *i++) return std::make_pair(i, true); return std::make_pair(i, false); } private: char c_; }; namespace asio { template <> struct is_match_condition<match_char> : public boost::true_type {}; } // namespace asio ... std::string data; asio::read_until(s, data, match_char('a')); </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 © 2003-2020 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="overload6.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../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="overload8.html"><img src="../../../next.png" alt="Next"></a> </div> </body> </html>