1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Daytime.4 - A synchronous UDP daytime client</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="../tutorial.html" title="Tutorial"> 9<link rel="prev" href="tutdaytime3/src.html" title="Source listing for Daytime.3"> 10<link rel="next" href="tutdaytime4/src.html" title="Source listing for Daytime.4"> 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="tutdaytime3/src.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.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="tutdaytime4/src.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.tutorial.tutdaytime4"></a><a class="link" href="tutdaytime4.html" title="Daytime.4 - A synchronous UDP daytime client">Daytime.4 - A synchronous 28 UDP daytime client</a> 29</h3></div></div></div> 30<p> 31 This tutorial program shows how to use asio to implement a client application 32 with UDP. 33 </p> 34<pre class="programlisting">#include <iostream> 35#include <boost/array.hpp> 36#include <boost/asio.hpp> 37 38using boost::asio::ip::udp; 39</pre> 40<p> 41 The start of the application is essentially the same as for the TCP daytime 42 client. 43 </p> 44<pre class="programlisting">int main(int argc, char* argv[]) 45{ 46 try 47 { 48 if (argc != 2) 49 { 50 std::cerr << "Usage: client <host>" << std::endl; 51 return 1; 52 } 53 54 boost::asio::io_context io_context; 55</pre> 56<p> 57 We use an <a class="link" href="../reference/ip__udp/resolver.html" title="ip::udp::resolver">ip::udp::resolver</a> 58 object to find the correct remote endpoint to use based on the host and service 59 names. The query is restricted to return only IPv4 endpoints by the <a class="link" href="../reference/ip__udp/v4.html" title="ip::udp::v4">ip::udp::v4()</a> argument. 60 </p> 61<pre class="programlisting"> udp::resolver resolver(io_context); 62 udp::endpoint receiver_endpoint = 63 *resolver.resolve(udp::v4(), argv[1], "daytime").begin(); 64</pre> 65<p> 66 The <a class="link" href="../reference/ip__basic_resolver/resolve.html" title="ip::basic_resolver::resolve">ip::udp::resolver::resolve()</a> 67 function is guaranteed to return at least one endpoint in the list if it 68 does not fail. This means it is safe to dereference the return value directly. 69 </p> 70<p> 71 Since UDP is datagram-oriented, we will not be using a stream socket. Create 72 an <a class="link" href="../reference/ip__udp/socket.html" title="ip::udp::socket">ip::udp::socket</a> 73 and initiate contact with the remote endpoint. 74 </p> 75<pre class="programlisting"> udp::socket socket(io_context); 76 socket.open(udp::v4()); 77 78 boost::array<char, 1> send_buf = {{ 0 }}; 79 socket.send_to(boost::asio::buffer(send_buf), receiver_endpoint); 80</pre> 81<p> 82 Now we need to be ready to accept whatever the server sends back to us. The 83 endpoint on our side that receives the server's response will be initialised 84 by <a class="link" href="../reference/basic_datagram_socket/receive_from.html" title="basic_datagram_socket::receive_from">ip::udp::socket::receive_from()</a>. 85 </p> 86<pre class="programlisting"> boost::array<char, 128> recv_buf; 87 udp::endpoint sender_endpoint; 88 size_t len = socket.receive_from( 89 boost::asio::buffer(recv_buf), sender_endpoint); 90 91 std::cout.write(recv_buf.data(), len); 92 } 93</pre> 94<p> 95 Finally, handle any exceptions that may have been thrown. 96 </p> 97<pre class="programlisting"> catch (std::exception& e) 98 { 99 std::cerr << e.what() << std::endl; 100 } 101 102 return 0; 103} 104</pre> 105<p> 106 See the <a class="link" href="tutdaytime4/src.html" title="Source listing for Daytime.4">full source listing</a> 107 </p> 108<p> 109 Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a> 110 </p> 111<p> 112 Previous: <a class="link" href="tutdaytime3.html" title="Daytime.3 - An asynchronous TCP daytime server">Daytime.3 - An 113 asynchronous TCP daytime server</a> 114 </p> 115<p> 116 Next: <a class="link" href="tutdaytime5.html" title="Daytime.5 - A synchronous UDP daytime server">Daytime.5 - A synchronous 117 UDP daytime server</a> 118 </p> 119</div> 120<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 121<td align="left"></td> 122<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 123 Kohlhoff<p> 124 Distributed under the Boost Software License, Version 1.0. (See accompanying 125 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>) 126 </p> 127</div></td> 128</tr></table> 129<hr> 130<div class="spirit-nav"> 131<a accesskey="p" href="tutdaytime3/src.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.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="tutdaytime4/src.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 132</div> 133</body> 134</html> 135
