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| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <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 |
| 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="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> |
| <span class="preprocessor">#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="preprocessor">#include</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">hpp</span><span class="special">></span> |
| |
| <span class="keyword">using</span> <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">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">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span> <span class="identifier">io_service</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_service</span><span class="special">);</span> |
| <span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">query</span> <span class="identifier">query</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> |
| </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> |
| <pre class="programlisting"> <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">query</span><span class="special">);</span> |
| </pre> |
| <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_service</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">boost</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">boost</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> |
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| Previous: <a class="link" href="tutdaytime3.html" title="Daytime.3 - An asynchronous TCP daytime server">Daytime.3 - An |
| asynchronous TCP daytime server</a> |
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| <p> |
| Next: <a class="link" href="tutdaytime5.html" title="Daytime.5 - A synchronous UDP daytime server">Daytime.5 - A synchronous |
| UDP daytime server</a> |
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| <td align="right"><div class="copyright-footer">Copyright © 2003 - 2010 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>) |
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