<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>async_connect (3 of 4 overloads)</title> <link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> <link rel="home" href="../../../boost_asio.html" title="Boost.Asio"> <link rel="up" href="../async_connect.html" title="async_connect"> <link rel="prev" href="overload2.html" title="async_connect (2 of 4 overloads)"> <link rel="next" href="overload4.html" title="async_connect (4 of 4 overloads)"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> <td align="center"><a href="../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="overload2.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="overload4.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h4 class="title"> <a name="boost_asio.reference.async_connect.overload3"></a><a class="link" href="overload3.html" title="async_connect (3 of 4 overloads)">async_connect (3 of 4 overloads)</a> </h4></div></div></div> <p> Asynchronously establishes a socket connection by trying each endpoint in a sequence. </p> <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <a class="link" href="../Protocol.html" title="Protocol requirements">Protocol</a><span class="special">,</span> <span class="keyword">typename</span> <a class="link" href="../SocketService.html" title="Socket service requirements">SocketService</a><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">ConnectCondition</span><span class="special">,</span> <span class="keyword">typename</span> <a class="link" href="../ComposedConnectHandler.html" title="Composed connect handler requirements">ComposedConnectHandler</a><span class="special">></span> <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.return_type_of_an_initiating_function"><span class="emphasis"><em>void-or-deduced</em></span></a> <span class="identifier">async_connect</span><span class="special">(</span> <span class="identifier">basic_socket</span><span class="special"><</span> <span class="identifier">Protocol</span><span class="special">,</span> <span class="identifier">SocketService</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">s</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="identifier">begin</span><span class="special">,</span> <span class="identifier">ConnectCondition</span> <span class="identifier">connect_condition</span><span class="special">,</span> <span class="identifier">ComposedConnectHandler</span> <span class="identifier">handler</span><span class="special">);</span> </pre> <p> This function attempts to connect a socket to one of a sequence of endpoints. It does this by repeated calls to the socket's <code class="computeroutput"><span class="identifier">async_connect</span></code> member function, once for each endpoint in the sequence, until a connection is successfully established. </p> <h6> <a name="boost_asio.reference.async_connect.overload3.h0"></a> <span class="phrase"><a name="boost_asio.reference.async_connect.overload3.parameters"></a></span><a class="link" href="overload3.html#boost_asio.reference.async_connect.overload3.parameters">Parameters</a> </h6> <div class="variablelist"> <p class="title"><b></b></p> <dl class="variablelist"> <dt><span class="term">s</span></dt> <dd><p> The socket to be connected. If the socket is already open, it will be closed. </p></dd> <dt><span class="term">begin</span></dt> <dd><p> An iterator pointing to the start of a sequence of endpoints. </p></dd> <dt><span class="term">connect_condition</span></dt> <dd> <p> A function object that is called prior to each connection attempt. The signature of the function object must be: </p> <pre class="programlisting"><span class="identifier">Iterator</span> <span class="identifier">connect_condition</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="identifier">next</span><span class="special">);</span> </pre> <p> The <code class="computeroutput"><span class="identifier">ec</span></code> parameter contains the result from the most recent connect operation. Before the first connection attempt, <code class="computeroutput"><span class="identifier">ec</span></code> is always set to indicate success. The <code class="computeroutput"><span class="identifier">next</span></code> parameter is an iterator pointing to the next endpoint to be tried. The function object should return the next iterator, but is permitted to return a different iterator so that endpoints may be skipped. The implementation guarantees that the function object will never be called with the end iterator. </p> </dd> <dt><span class="term">handler</span></dt> <dd> <p> The handler to be called when the connect operation completes. Copies will be made of the handler as required. The function signature of the handler must be: </p> <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span> <span class="comment">// Result of operation. if the sequence is empty, set to</span> <span class="comment">// boost::asio::error::not_found. Otherwise, contains the</span> <span class="comment">// error from the last connection attempt.</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">error</span><span class="special">,</span> <span class="comment">// On success, an iterator denoting the successfully</span> <span class="comment">// connected endpoint. Otherwise, the end iterator.</span> <span class="identifier">Iterator</span> <span class="identifier">iterator</span> <span class="special">);</span> </pre> <p> Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">post</span><span class="special">()</span></code>. </p> </dd> </dl> </div> <h6> <a name="boost_asio.reference.async_connect.overload3.h1"></a> <span class="phrase"><a name="boost_asio.reference.async_connect.overload3.remarks"></a></span><a class="link" href="overload3.html#boost_asio.reference.async_connect.overload3.remarks">Remarks</a> </h6> <p> This overload assumes that a default constructed object of type <code class="computeroutput"><span class="identifier">Iterator</span></code> represents the end of the sequence. This is a valid assumption for iterator types such as <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">iterator</span></code>. </p> <h6> <a name="boost_asio.reference.async_connect.overload3.h2"></a> <span class="phrase"><a name="boost_asio.reference.async_connect.overload3.example"></a></span><a class="link" href="overload3.html#boost_asio.reference.async_connect.overload3.example">Example</a> </h6> <p> The following connect condition function object can be used to output information about the individual connection attempts: </p> <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_connect_condition</span> <span class="special">{</span> <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">></span> <span class="identifier">Iterator</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="identifier">next</span><span class="special">)</span> <span class="special">{</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">ec</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Error: "</span> <span class="special"><<</span> <span class="identifier">ec</span><span class="special">.</span><span class="identifier">message</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Trying: "</span> <span class="special"><<</span> <span class="identifier">next</span><span class="special">-></span><span class="identifier">endpoint</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="keyword">return</span> <span class="identifier">next</span><span class="special">;</span> <span class="special">}</span> <span class="special">};</span> </pre> <p> It would be used with the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">connect</span></code> function as follows: </p> <pre class="programlisting"><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span> <span class="identifier">r</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">);</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">query</span> <span class="identifier">q</span><span class="special">(</span><span class="string">"host"</span><span class="special">,</span> <span class="string">"service"</span><span class="special">);</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">s</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">);</span> <span class="comment">// ...</span> <span class="identifier">r</span><span class="special">.</span><span class="identifier">async_resolve</span><span class="special">(</span><span class="identifier">q</span><span class="special">,</span> <span class="identifier">resolve_handler</span><span class="special">);</span> <span class="comment">// ...</span> <span class="keyword">void</span> <span class="identifier">resolve_handler</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">i</span><span class="special">)</span> <span class="special">{</span> <span class="keyword">if</span> <span class="special">(!</span><span class="identifier">ec</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_connect</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">i</span><span class="special">,</span> <span class="identifier">my_connect_condition</span><span class="special">(),</span> <span class="identifier">connect_handler</span><span class="special">);</span> <span class="special">}</span> <span class="special">}</span> <span class="comment">// ...</span> <span class="keyword">void</span> <span class="identifier">connect_handler</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">i</span><span class="special">)</span> <span class="special">{</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">ec</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// An error occurred.</span> <span class="special">}</span> <span class="keyword">else</span> <span class="special">{</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Connected to: "</span> <span class="special"><<</span> <span class="identifier">i</span><span class="special">-></span><span class="identifier">endpoint</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="special">}</span> <span class="special">}</span> </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 © 2003-2015 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="overload2.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="overload4.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>