1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Resolve handler requirements</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="../reference.html" title="Reference"> 9<link rel="prev" href="Receiver.html" title="Receiver concepts"> 10<link rel="next" href="Scheduler.html" title="Scheduler concept"> 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="Receiver.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.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="Scheduler.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="boost_asio.reference.ResolveHandler"></a><a class="link" href="ResolveHandler.html" title="Resolve handler requirements">Resolve handler 28 requirements</a> 29</h3></div></div></div> 30<p> 31 A resolve handler must meet the requirements for a <a class="link" href="Handler.html" title="Handlers">handler</a>. 32 A value <code class="computeroutput">h</code> of a resolve handler class should work correctly in 33 the expression <code class="computeroutput">h(ec, r)</code>, where <code class="computeroutput">ec</code> is an lvalue 34 of type <code class="computeroutput">const error_code</code> and <code class="computeroutput">r</code> is an lvalue of 35 type <code class="computeroutput">const ip::basic_resolver_results<InternetProtocol></code>. 36 <code class="computeroutput">InternetProtocol</code> is the template parameter of the <a class="link" href="ip__basic_resolver.html" title="ip::basic_resolver"><code class="computeroutput">ip::basic_resolver<></code></a> 37 which is used to initiate the asynchronous operation. 38 </p> 39<h5> 40<a name="boost_asio.reference.ResolveHandler.h0"></a> 41 <span class="phrase"><a name="boost_asio.reference.ResolveHandler.examples"></a></span><a class="link" href="ResolveHandler.html#boost_asio.reference.ResolveHandler.examples">Examples</a> 42 </h5> 43<p> 44 A free function as a resolve handler: 45 </p> 46<pre class="programlisting">void resolve_handler( 47 const boost::system::error_code& ec, 48 boost::asio::ip::tcp::resolver::results_type results) 49{ 50 ... 51} 52</pre> 53<p> 54 A resolve handler function object: 55 </p> 56<pre class="programlisting">struct resolve_handler 57{ 58 ... 59 void operator()( 60 const boost::system::error_code& ec, 61 boost::asio::ip::tcp::resolver::results_type results) 62 { 63 ... 64 } 65 ... 66}; 67</pre> 68<p> 69 A lambda as a resolve handler: 70 </p> 71<pre class="programlisting">resolver.async_resolve(..., 72 [](const boost::system::error_code& ec, 73 boost::asio::ip::tcp::resolver::results_type results) 74 { 75 ... 76 }); 77</pre> 78<p> 79 A non-static class member function adapted to a resolve handler using <code class="computeroutput">std::bind()</code>: 80 </p> 81<pre class="programlisting">void my_class::resolve_handler( 82 const boost::system::error_code& ec, 83 boost::asio::ip::tcp::resolver::results_type results) 84{ 85 ... 86} 87... 88resolver.async_resolve(..., 89 std::bind(&my_class::resolve_handler, 90 this, std::placeholders::_1, 91 std::placeholders::_2)); 92</pre> 93<p> 94 A non-static class member function adapted to a resolve handler using <code class="computeroutput">boost::bind()</code>: 95 </p> 96<pre class="programlisting">void my_class::resolve_handler( 97 const boost::system::error_code& ec, 98 boost::asio::ip::tcp::resolver::results_type results) 99{ 100 ... 101} 102... 103resolver.async_resolve(..., 104 boost::bind(&my_class::resolve_handler, 105 this, boost::asio::placeholders::error, 106 boost::asio::placeholders::results)); 107</pre> 108</div> 109<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 110<td align="left"></td> 111<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 112 Kohlhoff<p> 113 Distributed under the Boost Software License, Version 1.0. (See accompanying 114 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>) 115 </p> 116</div></td> 117</tr></table> 118<hr> 119<div class="spirit-nav"> 120<a accesskey="p" href="Receiver.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.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="Scheduler.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 121</div> 122</body> 123</html> 124
