doc/html/boost_asio/tutorial/tutdaytime1.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>Daytime.1 - A synchronous TCP 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="tuttimer5/src.html" title="Source listing for Timer.5">
  10 <link rel="next" href="tutdaytime1/src.html" title="Source listing for Daytime.1">
  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="tuttimer5/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="tutdaytime1/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.tutdaytime1"></a><a class="link" href="tutdaytime1.html" title="Daytime.1 - A synchronous TCP daytime client">Daytime.1 - A synchronous
  28       TCP 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 TCP.
  33       </p>
  34 <p>
  35         We start by including the necessary header files.
  36       </p>
  37 <pre class="programlisting"><span class="special">#</span><span class="identifier">include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
  38 <span class="special">#</span><span class="identifier">include</span> <span class="special">&lt;</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">&gt;</span>
  39 <span class="special">#</span><span class="identifier">include</span> <span class="special">&lt;</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">&gt;</span>
  40 </pre>
  41 <p>
  42         The purpose of this application is to access a daytime service, so we need
  43         the user to specify the server.
  44       </p>
  45 <pre class="programlisting"><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">tcp</span><span class="special">;</span>
  46
  47 <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>
  48 <span class="special">{</span>
  49   <span class="keyword">try</span>
  50   <span class="special">{</span>
  51     <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>
  52     <span class="special">{</span>
  53       <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special">&lt;&lt;</span> <span class="string">"Usage: client &lt;host&gt;"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
  54       <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
  55     <span class="special">}</span>
  56 </pre>
  57 <p>
  58         All programs that use asio need to have at least one <a class="link" href="../reference/io_service.html" title="io_service">io_service</a>
  59         object.
  60       </p>
  61 <pre class="programlisting">    <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>
  62 </pre>
  63 <p>
  64         We need to turn the server name that was specified as a parameter to the
  65         application, into a TCP endpoint. To do this we use an <a class="link" href="../reference/ip__tcp/resolver.html" title="ip::tcp::resolver">ip::tcp::resolver</a>
  66         object.
  67       </p>
  68 <pre class="programlisting">    <span class="identifier">tcp</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>
  69 </pre>
  70 <p>
  71         A resolver takes a query object and turns it into a list of endpoints. We
  72         construct a query using the name of the server, specified in <code class="computeroutput"><span class="identifier">argv</span><span class="special">[</span><span class="number">1</span><span class="special">]</span></code>, and the name of the service, in this case
  73         <code class="computeroutput"><span class="string">"daytime"</span></code>.
  74       </p>
  75 <pre class="programlisting">    <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">query</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>
  76 </pre>
  77 <p>
  78         The list of endpoints is returned using an iterator of type <a class="link" href="../reference/ip__basic_resolver/iterator.html" title="ip::basic_resolver::iterator">ip::tcp::resolver::iterator</a>.
  79         (Note that a default constructed <a class="link" href="../reference/ip__basic_resolver/iterator.html" title="ip::basic_resolver::iterator">ip::tcp::resolver::iterator</a>
  80         object can be used as an end iterator.)
  81       </p>
  82 <pre class="programlisting">    <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">endpoint_iterator</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>
  83 </pre>
  84 <p>
  85         Now we create and connect the socket. The list of endpoints obtained above
  86         may contain both IPv4 and IPv6 endpoints, so we need to try each of them
  87         until we find one that works. This keeps the client program independent of
  88         a specific IP version. The boost::asio::connect() function does this for
  89         us automatically.
  90       </p>
  91 <pre class="programlisting">    <span class="identifier">tcp</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>
  92     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">connect</span><span class="special">(</span><span class="identifier">socket</span><span class="special">,</span> <span class="identifier">endpoint_iterator</span><span class="special">);</span>
  93 </pre>
  94 <p>
  95         The connection is open. All we need to do now is read the response from the
  96         daytime service.
  97       </p>
  98 <p>
  99         We use a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span></code> to hold the received data. The boost::asio::buffer()
 100         function automatically determines the size of the array to help prevent buffer
 101         overruns. Instead of a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span></code>,
 102         we could have used a <code class="computeroutput"><span class="keyword">char</span> <span class="special">[]</span></code>
 103         or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span></code>.
 104       </p>
 105 <pre class="programlisting">    <span class="keyword">for</span> <span class="special">(;;)</span>
 106     <span class="special">{</span>
 107       <span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">,</span> <span class="number">128</span><span class="special">&gt;</span> <span class="identifier">buf</span><span class="special">;</span>
 108       <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="identifier">error</span><span class="special">;</span>
 109
 110       <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">read_some</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">buf</span><span class="special">),</span> <span class="identifier">error</span><span class="special">);</span>
 111 </pre>
 112 <p>
 113         When the server closes the connection, the <a class="link" href="../reference/basic_stream_socket/read_some.html" title="basic_stream_socket::read_some">ip::tcp::socket::read_some()</a>
 114         function will exit with the boost::asio::error::eof error, which is how we
 115         know to exit the loop.
 116       </p>
 117 <pre class="programlisting">      <span class="keyword">if</span> <span class="special">(</span><span class="identifier">error</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">error</span><span class="special">::</span><span class="identifier">eof</span><span class="special">)</span>
 118         <span class="keyword">break</span><span class="special">;</span> <span class="comment">// Connection closed cleanly by peer.</span>
 119       <span class="keyword">else</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">error</span><span class="special">)</span>
 120         <span class="keyword">throw</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">system_error</span><span class="special">(</span><span class="identifier">error</span><span class="special">);</span> <span class="comment">// Some other error.</span>
 121
 122       <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">buf</span><span class="special">.</span><span class="identifier">data</span><span class="special">(),</span> <span class="identifier">len</span><span class="special">);</span>
 123     <span class="special">}</span>
 124 </pre>
 125 <p>
 126         Finally, handle any exceptions that may have been thrown.
 127       </p>
 128 <pre class="programlisting">  <span class="special">}</span>
 129   <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">&amp;</span> <span class="identifier">e</span><span class="special">)</span>
 130   <span class="special">{</span>
 131     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special">&lt;&lt;</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 132   <span class="special">}</span>
 133 </pre>
 134 <p>
 135         See the <a class="link" href="tutdaytime1/src.html" title="Source listing for Daytime.1">full source listing</a>
 136       </p>
 137 <p>
 138         Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a>
 139       </p>
 140 <p>
 141         Next: <a class="link" href="tutdaytime2.html" title="Daytime.2 - A synchronous TCP daytime server">Daytime.2 - A synchronous
 142         TCP daytime server</a>
 143       </p>
 144 </div>
 145 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 146 <td align="left"></td>
 147 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2017 Christopher M. Kohlhoff<p>
 148         Distributed under the Boost Software License, Version 1.0. (See accompanying
 149         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>)
 150       </p>
 151 </div></td>
 152 </tr></table>
 153 <hr>
 154 <div class="spirit-nav">
 155 <a accesskey="p" href="tuttimer5/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="tutdaytime1/src.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
 156 </div>
 157 </body>
 158 </html>