1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>async_connect (6 of 6 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="../async_connect.html" title="async_connect"> 9<link rel="prev" href="overload5.html" title="async_connect (5 of 6 overloads)"> 10<link rel="next" href="../async_initiate.html" title="async_initiate"> 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="overload5.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../async_connect.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="../async_initiate.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.async_connect.overload6"></a><a class="link" href="overload6.html" title="async_connect (6 of 6 overloads)">async_connect 28 (6 of 6 overloads)</a> 29</h4></div></div></div> 30<p> 31 Asynchronously establishes a socket connection by trying each endpoint 32 in a sequence. 33 </p> 34<pre class="programlisting">template< 35 typename <a class="link" href="../Protocol.html" title="Protocol requirements">Protocol</a>, 36 typename <a class="link" href="../Executor1.html" title="Executor requirements">Executor</a>, 37 typename Iterator, 38 typename <a class="link" href="../ConnectCondition.html" title="Connect condition requirements">ConnectCondition</a>, 39 typename <a class="link" href="../IteratorConnectHandler.html" title="Iterator connect handler requirements">IteratorConnectHandler</a> = <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>> 40<a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_connect( 41 basic_socket< Protocol, Executor > & s, 42 Iterator begin, 43 Iterator end, 44 ConnectCondition connect_condition, 45 IteratorConnectHandler && handler = <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>); 46</pre> 47<p> 48 This function attempts to connect a socket to one of a sequence of endpoints. 49 It does this by repeated calls to the socket's <code class="computeroutput">async_connect</code> 50 member function, once for each endpoint in the sequence, until a connection 51 is successfully established. 52 </p> 53<h6> 54<a name="boost_asio.reference.async_connect.overload6.h0"></a> 55 <span class="phrase"><a name="boost_asio.reference.async_connect.overload6.parameters"></a></span><a class="link" href="overload6.html#boost_asio.reference.async_connect.overload6.parameters">Parameters</a> 56 </h6> 57<div class="variablelist"> 58<p class="title"><b></b></p> 59<dl class="variablelist"> 60<dt><span class="term">s</span></dt> 61<dd><p> 62 The socket to be connected. If the socket is already open, it will 63 be closed. 64 </p></dd> 65<dt><span class="term">begin</span></dt> 66<dd><p> 67 An iterator pointing to the start of a sequence of endpoints. 68 </p></dd> 69<dt><span class="term">end</span></dt> 70<dd><p> 71 An iterator pointing to the end of a sequence of endpoints. 72 </p></dd> 73<dt><span class="term">connect_condition</span></dt> 74<dd> 75<p> 76 A function object that is called prior to each connection attempt. 77 The signature of the function object must be: 78</p> 79<pre class="programlisting">bool connect_condition( 80 const boost::system::error_code& ec, 81 const typename Protocol::endpoint& next); 82</pre> 83<p> 84 The <code class="computeroutput">ec</code> parameter contains the result from the most recent 85 connect operation. Before the first connection attempt, <code class="computeroutput">ec</code> 86 is always set to indicate success. The <code class="computeroutput">next</code> parameter 87 is the next endpoint to be tried. The function object should return 88 true if the next endpoint should be tried, and false if it should 89 be skipped. 90 </p> 91</dd> 92<dt><span class="term">handler</span></dt> 93<dd> 94<p> 95 The handler to be called when the connect operation completes. Copies 96 will be made of the handler as required. The function signature of 97 the handler must be: 98</p> 99<pre class="programlisting">void handler( 100 // Result of operation. if the sequence is empty, set to 101 // boost::asio::error::not_found. Otherwise, contains the 102 // error from the last connection attempt. 103 const boost::system::error_code& error, 104 105 // On success, an iterator denoting the successfully 106 // connected endpoint. Otherwise, the end iterator. 107 Iterator iterator 108); 109</pre> 110<p> 111 Regardless of whether the asynchronous operation completes immediately 112 or not, the handler will not be invoked from within this function. 113 On immediate completion, invocation of the handler will be performed 114 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>. 115 </p> 116</dd> 117</dl> 118</div> 119<h6> 120<a name="boost_asio.reference.async_connect.overload6.h1"></a> 121 <span class="phrase"><a name="boost_asio.reference.async_connect.overload6.example"></a></span><a class="link" href="overload6.html#boost_asio.reference.async_connect.overload6.example">Example</a> 122 </h6> 123<p> 124 The following connect condition function object can be used to output information 125 about the individual connection attempts: 126 </p> 127<pre class="programlisting">struct my_connect_condition 128{ 129 bool operator()( 130 const boost::system::error_code& ec, 131 const::tcp::endpoint& next) 132 { 133 if (ec) std::cout << "Error: " << ec.message() << std::endl; 134 std::cout << "Trying: " << next << std::endl; 135 return true; 136 } 137}; 138</pre> 139<p> 140 It would be used with the <code class="computeroutput">boost::asio::connect</code> function as 141 follows: 142 </p> 143<pre class="programlisting">tcp::resolver r(my_context); 144tcp::resolver::query q("host", "service"); 145tcp::socket s(my_context); 146 147// ... 148 149r.async_resolve(q, resolve_handler); 150 151// ... 152 153void resolve_handler( 154 const boost::system::error_code& ec, 155 tcp::resolver::iterator i) 156{ 157 if (!ec) 158 { 159 tcp::resolver::iterator end; 160 boost::asio::async_connect(s, i, end, 161 my_connect_condition(), 162 connect_handler); 163 } 164} 165 166// ... 167 168void connect_handler( 169 const boost::system::error_code& ec, 170 tcp::resolver::iterator i) 171{ 172 if (ec) 173 { 174 // An error occurred. 175 } 176 else 177 { 178 std::cout << "Connected to: " << i->endpoint() << std::endl; 179 } 180} 181</pre> 182</div> 183<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 184<td align="left"></td> 185<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 186 Kohlhoff<p> 187 Distributed under the Boost Software License, Version 1.0. (See accompanying 188 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>) 189 </p> 190</div></td> 191</tr></table> 192<hr> 193<div class="spirit-nav"> 194<a accesskey="p" href="overload5.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../async_connect.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="../async_initiate.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 195</div> 196</body> 197</html> 198
