1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>connect (7 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="overload6.html" title="connect (6 of 12 overloads)"> 10<link rel="next" href="overload8.html" title="connect (8 of 12 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="overload6.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="overload8.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.overload7"></a><a class="link" href="overload7.html" title="connect (7 of 12 overloads)">connect (7 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 <a class="link" href="../EndpointSequence.html" title="Endpoint sequence requirements">EndpointSequence</a>, 37 typename <a class="link" href="../ConnectCondition.html" title="Connect condition requirements">ConnectCondition</a>> 38Protocol::endpoint connect( 39 basic_socket< Protocol, Executor > & s, 40 const EndpointSequence & endpoints, 41 ConnectCondition connect_condition, 42 typename enable_if< is_endpoint_sequence< EndpointSequence >::value >::type * = 0); 43</pre> 44<p> 45 This function attempts to connect a socket to one of a sequence of endpoints. 46 It does this by repeated calls to the socket's <code class="computeroutput">connect</code> member 47 function, once for each endpoint in the sequence, until a connection is 48 successfully established. 49 </p> 50<h6> 51<a name="boost_asio.reference.connect.overload7.h0"></a> 52 <span class="phrase"><a name="boost_asio.reference.connect.overload7.parameters"></a></span><a class="link" href="overload7.html#boost_asio.reference.connect.overload7.parameters">Parameters</a> 53 </h6> 54<div class="variablelist"> 55<p class="title"><b></b></p> 56<dl class="variablelist"> 57<dt><span class="term">s</span></dt> 58<dd><p> 59 The socket to be connected. If the socket is already open, it will 60 be closed. 61 </p></dd> 62<dt><span class="term">endpoints</span></dt> 63<dd><p> 64 A sequence of endpoints. 65 </p></dd> 66<dt><span class="term">connect_condition</span></dt> 67<dd> 68<p> 69 A function object that is called prior to each connection attempt. 70 The signature of the function object must be: 71</p> 72<pre class="programlisting">bool connect_condition( 73 const boost::system::error_code& ec, 74 const typename Protocol::endpoint& next); 75</pre> 76<p> 77 The <code class="computeroutput">ec</code> parameter contains the result from the most recent 78 connect operation. Before the first connection attempt, <code class="computeroutput">ec</code> 79 is always set to indicate success. The <code class="computeroutput">next</code> parameter 80 is the next endpoint to be tried. The function object should return 81 true if the next endpoint should be tried, and false if it should 82 be skipped. 83 </p> 84</dd> 85</dl> 86</div> 87<h6> 88<a name="boost_asio.reference.connect.overload7.h1"></a> 89 <span class="phrase"><a name="boost_asio.reference.connect.overload7.return_value"></a></span><a class="link" href="overload7.html#boost_asio.reference.connect.overload7.return_value">Return Value</a> 90 </h6> 91<p> 92 The successfully connected endpoint. 93 </p> 94<h6> 95<a name="boost_asio.reference.connect.overload7.h2"></a> 96 <span class="phrase"><a name="boost_asio.reference.connect.overload7.exceptions"></a></span><a class="link" href="overload7.html#boost_asio.reference.connect.overload7.exceptions">Exceptions</a> 97 </h6> 98<div class="variablelist"> 99<p class="title"><b></b></p> 100<dl class="variablelist"> 101<dt><span class="term">boost::system::system_error</span></dt> 102<dd><p> 103 Thrown on failure. If the sequence is empty, the associated <code class="computeroutput">error_code</code> 104 is <code class="computeroutput">boost::asio::error::not_found</code>. Otherwise, contains 105 the error from the last connection attempt. 106 </p></dd> 107</dl> 108</div> 109<h6> 110<a name="boost_asio.reference.connect.overload7.h3"></a> 111 <span class="phrase"><a name="boost_asio.reference.connect.overload7.example"></a></span><a class="link" href="overload7.html#boost_asio.reference.connect.overload7.example">Example</a> 112 </h6> 113<p> 114 The following connect condition function object can be used to output information 115 about the individual connection attempts: 116 </p> 117<pre class="programlisting">struct my_connect_condition 118{ 119 bool operator()( 120 const boost::system::error_code& ec, 121 const::tcp::endpoint& next) 122 { 123 if (ec) std::cout << "Error: " << ec.message() << std::endl; 124 std::cout << "Trying: " << next << std::endl; 125 return true; 126 } 127}; 128</pre> 129<p> 130 It would be used with the <code class="computeroutput">boost::asio::connect</code> function as 131 follows: 132 </p> 133<pre class="programlisting">tcp::resolver r(my_context); 134tcp::resolver::query q("host", "service"); 135tcp::socket s(my_context); 136tcp::endpoint e = boost::asio::connect(s, 137 r.resolve(q), my_connect_condition()); 138std::cout << "Connected to: " << e << std::endl; 139</pre> 140</div> 141<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 142<td align="left"></td> 143<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 144 Kohlhoff<p> 145 Distributed under the Boost Software License, Version 1.0. (See accompanying 146 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>) 147 </p> 148</div></td> 149</tr></table> 150<hr> 151<div class="spirit-nav"> 152<a accesskey="p" href="overload6.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="overload8.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 153</div> 154</body> 155</html> 156
