1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>connect (12 of 12 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="../connect.html" title="connect"> 9<link rel="prev" href="overload11.html" title="connect (11 of 12 overloads)"> 10<link rel="next" href="../const_buffer.html" title="const_buffer"> 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="overload11.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../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="../const_buffer.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.connect.overload12"></a><a class="link" href="overload12.html" title="connect (12 of 12 overloads)">connect (12 28 of 12 overloads)</a> 29</h4></div></div></div> 30<p> 31 Establishes a socket connection by trying each endpoint in a sequence. 32 </p> 33<pre class="programlisting">template< 34 typename <a class="link" href="../Protocol.html" title="Protocol requirements">Protocol</a>, 35 typename <a class="link" href="../Executor1.html" title="Executor requirements">Executor</a>, 36 typename Iterator, 37 typename <a class="link" href="../ConnectCondition.html" title="Connect condition requirements">ConnectCondition</a>> 38Iterator connect( 39 basic_socket< Protocol, Executor > & s, 40 Iterator begin, 41 Iterator end, 42 ConnectCondition connect_condition, 43 boost::system::error_code & ec); 44</pre> 45<p> 46 This function attempts to connect a socket to one of a sequence of endpoints. 47 It does this by repeated calls to the socket's <code class="computeroutput">connect</code> member 48 function, once for each endpoint in the sequence, until a connection is 49 successfully established. 50 </p> 51<h6> 52<a name="boost_asio.reference.connect.overload12.h0"></a> 53 <span class="phrase"><a name="boost_asio.reference.connect.overload12.parameters"></a></span><a class="link" href="overload12.html#boost_asio.reference.connect.overload12.parameters">Parameters</a> 54 </h6> 55<div class="variablelist"> 56<p class="title"><b></b></p> 57<dl class="variablelist"> 58<dt><span class="term">s</span></dt> 59<dd><p> 60 The socket to be connected. If the socket is already open, it will 61 be closed. 62 </p></dd> 63<dt><span class="term">begin</span></dt> 64<dd><p> 65 An iterator pointing to the start of a sequence of endpoints. 66 </p></dd> 67<dt><span class="term">end</span></dt> 68<dd><p> 69 An iterator pointing to the end of a sequence of endpoints. 70 </p></dd> 71<dt><span class="term">connect_condition</span></dt> 72<dd> 73<p> 74 A function object that is called prior to each connection attempt. 75 The signature of the function object must be: 76</p> 77<pre class="programlisting">bool connect_condition( 78 const boost::system::error_code& ec, 79 const typename Protocol::endpoint& next); 80</pre> 81<p> 82 The <code class="computeroutput">ec</code> parameter contains the result from the most recent 83 connect operation. Before the first connection attempt, <code class="computeroutput">ec</code> 84 is always set to indicate success. The <code class="computeroutput">next</code> parameter 85 is the next endpoint to be tried. The function object should return 86 true if the next endpoint should be tried, and false if it should 87 be skipped. 88 </p> 89</dd> 90<dt><span class="term">ec</span></dt> 91<dd><p> 92 Set to indicate what error occurred, if any. If the sequence is empty, 93 set to <code class="computeroutput">boost::asio::error::not_found</code>. Otherwise, contains 94 the error from the last connection attempt. 95 </p></dd> 96</dl> 97</div> 98<h6> 99<a name="boost_asio.reference.connect.overload12.h1"></a> 100 <span class="phrase"><a name="boost_asio.reference.connect.overload12.return_value"></a></span><a class="link" href="overload12.html#boost_asio.reference.connect.overload12.return_value">Return Value</a> 101 </h6> 102<p> 103 On success, an iterator denoting the successfully connected endpoint. Otherwise, 104 the end iterator. 105 </p> 106<h6> 107<a name="boost_asio.reference.connect.overload12.h2"></a> 108 <span class="phrase"><a name="boost_asio.reference.connect.overload12.example"></a></span><a class="link" href="overload12.html#boost_asio.reference.connect.overload12.example">Example</a> 109 </h6> 110<p> 111 The following connect condition function object can be used to output information 112 about the individual connection attempts: 113 </p> 114<pre class="programlisting">struct my_connect_condition 115{ 116 bool operator()( 117 const boost::system::error_code& ec, 118 const::tcp::endpoint& next) 119 { 120 if (ec) std::cout << "Error: " << ec.message() << std::endl; 121 std::cout << "Trying: " << next << std::endl; 122 return true; 123 } 124}; 125</pre> 126<p> 127 It would be used with the <code class="computeroutput">boost::asio::connect</code> function as 128 follows: 129 </p> 130<pre class="programlisting">tcp::resolver r(my_context); 131tcp::resolver::query q("host", "service"); 132tcp::resolver::results_type e = r.resolve(q); 133tcp::socket s(my_context); 134boost::system::error_code ec; 135tcp::resolver::results_type::iterator i = boost::asio::connect( 136 s, e.begin(), e.end(), my_connect_condition()); 137if (ec) 138{ 139 // An error occurred. 140} 141else 142{ 143 std::cout << "Connected to: " << i->endpoint() << std::endl; 144} 145</pre> 146</div> 147<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 148<td align="left"></td> 149<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 150 Kohlhoff<p> 151 Distributed under the Boost Software License, Version 1.0. (See accompanying 152 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>) 153 </p> 154</div></td> 155</tr></table> 156<hr> 157<div class="spirit-nav"> 158<a accesskey="p" href="overload11.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../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="../const_buffer.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 159</div> 160</body> 161</html> 162
