<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Daytime.4 - A synchronous UDP daytime client</title> <link rel="stylesheet" href="../../boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../../index.html" title="Asio"> <link rel="up" href="../tutorial.html" title="Tutorial"> <link rel="prev" href="tutdaytime3/src.html" title="Source listing for Daytime.3"> <link rel="next" href="tutdaytime4/src.html" title="Source listing for Daytime.4"> <meta name="viewport" content="width=device-width, initial-scale=1"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../asio.png"></td></tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="tutdaytime3/src.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.html"><img src="../../up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../home.png" alt="Home"></a><a accesskey="n" href="tutdaytime4/src.html"><img src="../../next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="asio.tutorial.tutdaytime4"></a><a class="link" href="tutdaytime4.html" title="Daytime.4 - A synchronous UDP daytime client">Daytime.4 - A synchronous UDP daytime client</a> </h3></div></div></div> <p> This tutorial program shows how to use asio to implement a client application with UDP. </p> <pre class="programlisting"><span class="special">#</span><span class="identifier">include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> <span class="special">#</span><span class="identifier">include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">array</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> <span class="special">#</span><span class="identifier">include</span> <span class="special"><</span><span class="identifier">asio</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> <span class="keyword">using</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">;</span> </pre> <p> The start of the application is essentially the same as for the TCP daytime client. </p> <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">argc</span><span class="special">,</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">argv</span><span class="special">[])</span> <span class="special">{</span> <span class="keyword">try</span> <span class="special">{</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">argc</span> <span class="special">!=</span> <span class="number">2</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="string">"Usage: client <host>"</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="number">1</span><span class="special">;</span> <span class="special">}</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span> <span class="identifier">io_context</span><span class="special">;</span> </pre> <p> We use an <a class="link" href="../reference/ip__udp/resolver.html" title="ip::udp::resolver">ip::udp::resolver</a> object to find the correct remote endpoint to use based on the host and service 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. </p> <pre class="programlisting"> <span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span> <span class="identifier">resolver</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">);</span> <span class="identifier">udp</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="identifier">receiver_endpoint</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">resolver</span><span class="special">.</span><span class="identifier">resolve</span><span class="special">(</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">v4</span><span class="special">(),</span> <span class="identifier">argv</span><span class="special">[</span><span class="number">1</span><span class="special">],</span> <span class="string">"daytime"</span><span class="special">).</span><span class="identifier">begin</span><span class="special">();</span> </pre> <p> The <a class="link" href="../reference/ip__basic_resolver/resolve.html" title="ip::basic_resolver::resolve">ip::udp::resolver::resolve()</a> function is guaranteed to return at least one endpoint in the list if it does not fail. This means it is safe to dereference the return value directly. </p> <p> Since UDP is datagram-oriented, we will not be using a stream socket. Create an <a class="link" href="../reference/ip__udp/socket.html" title="ip::udp::socket">ip::udp::socket</a> and initiate contact with the remote endpoint. </p> <pre class="programlisting"> <span class="identifier">udp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">);</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">open</span><span class="special">(</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">v4</span><span class="special">());</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="number">1</span><span class="special">></span> <span class="identifier">send_buf</span> <span class="special">=</span> <span class="special">{{</span> <span class="number">0</span> <span class="special">}};</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">send_to</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">send_buf</span><span class="special">),</span> <span class="identifier">receiver_endpoint</span><span class="special">);</span> </pre> <p> Now we need to be ready to accept whatever the server sends back to us. The endpoint on our side that receives the server's response will be initialised by <a class="link" href="../reference/basic_datagram_socket/receive_from.html" title="basic_datagram_socket::receive_from">ip::udp::socket::receive_from()</a>. </p> <pre class="programlisting"> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="number">128</span><span class="special">></span> <span class="identifier">recv_buf</span><span class="special">;</span> <span class="identifier">udp</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="identifier">sender_endpoint</span><span class="special">;</span> <span class="identifier">size_t</span> <span class="identifier">len</span> <span class="special">=</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">receive_from</span><span class="special">(</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">recv_buf</span><span class="special">),</span> <span class="identifier">sender_endpoint</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="identifier">write</span><span class="special">(</span><span class="identifier">recv_buf</span><span class="special">.</span><span class="identifier">data</span><span class="special">(),</span> <span class="identifier">len</span><span class="special">);</span> <span class="special">}</span> </pre> <p> Finally, handle any exceptions that may have been thrown. </p> <pre class="programlisting"> <span class="keyword">catch</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span class="special">&</span> <span class="identifier">e</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</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="keyword">return</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> </pre> <p> See the <a class="link" href="tutdaytime4/src.html" title="Source listing for Daytime.4">full source listing</a> </p> <p> Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a> </p> <p> Previous: <a class="link" href="tutdaytime3.html" title="Daytime.3 - An asynchronous TCP daytime server">Daytime.3 - An asynchronous TCP daytime server</a> </p> <p> Next: <a class="link" href="tutdaytime5.html" title="Daytime.5 - A synchronous UDP daytime server">Daytime.5 - A synchronous UDP daytime server</a> </p> </div> <div class="copyright-footer">Copyright © 2003-2023 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> <hr> <div class="spirit-nav"> <a accesskey="p" href="tutdaytime3/src.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.html"><img src="../../up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../home.png" alt="Home"></a><a accesskey="n" href="tutdaytime4/src.html"><img src="../../next.png" alt="Next"></a> </div> </body> </html>