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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_asio.tutorial.tutdaytime3"></a><a class="link" href="tutdaytime3.html" title="Daytime.3 - An asynchronous TCP daytime server">Daytime.3 - An asynchronous
  28       TCP daytime server</a>
  29 </h3></div></div></div>
  30 <h5>
  31 <a name="boost_asio.tutorial.tutdaytime3.h0"></a>
  32         <span class="phrase"><a name="boost_asio.tutorial.tutdaytime3.the_main___function"></a></span><a class="link" href="tutdaytime3.html#boost_asio.tutorial.tutdaytime3.the_main___function">The
  33         main() function</a>
  34       </h5>
  35 <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
  36 <span class="special">{</span>
  37   <span class="keyword">try</span>
  38   <span class="special">{</span>
  39 </pre>
  40 <p>
  41         We need to create a server object to accept incoming client connections.
  42         The <a class="link" href="../reference/io_service.html" title="io_service">io_service</a> object
  43         provides I/O services, such as sockets, that the server object will use.
  44       </p>
  45 <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>
  46     <span class="identifier">tcp_server</span> <span class="identifier">server</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">);</span>
  47 </pre>
  48 <p>
  49         Run the <a class="link" href="../reference/io_service.html" title="io_service">io_service</a>
  50         object so that it will perform asynchronous operations on your behalf.
  51       </p>
  52 <pre class="programlisting">    <span class="identifier">io_service</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span>
  53   <span class="special">}</span>
  54   <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>
  55   <span class="special">{</span>
  56     <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>
  57   <span class="special">}</span>
  58
  59   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
  60 <span class="special">}</span>
  61 </pre>
  62 <h5>
  63 <a name="boost_asio.tutorial.tutdaytime3.h1"></a>
  64         <span class="phrase"><a name="boost_asio.tutorial.tutdaytime3.the_tcp_server_class"></a></span><a class="link" href="tutdaytime3.html#boost_asio.tutorial.tutdaytime3.the_tcp_server_class">The tcp_server
  65         class</a>
  66       </h5>
  67 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">tcp_server</span>
  68 <span class="special">{</span>
  69 <span class="keyword">public</span><span class="special">:</span>
  70 </pre>
  71 <p>
  72         The constructor initialises an acceptor to listen on TCP port 13.
  73       </p>
  74 <pre class="programlisting">  <span class="identifier">tcp_server</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="special">&amp;</span> <span class="identifier">io_service</span><span class="special">)</span>
  75     <span class="special">:</span> <span class="identifier">acceptor_</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">,</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">endpoint</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">v4</span><span class="special">(),</span> <span class="number">13</span><span class="special">))</span>
  76   <span class="special">{</span>
  77     <span class="identifier">start_accept</span><span class="special">();</span>
  78   <span class="special">}</span>
  79
  80 <span class="keyword">private</span><span class="special">:</span>
  81 </pre>
  82 <p>
  83         The function <code class="computeroutput"><span class="identifier">start_accept</span><span class="special">()</span></code> creates a socket and initiates an asynchronous
  84         accept operation to wait for a new connection.
  85       </p>
  86 <pre class="programlisting">  <span class="keyword">void</span> <span class="identifier">start_accept</span><span class="special">()</span>
  87   <span class="special">{</span>
  88     <span class="identifier">tcp_connection</span><span class="special">::</span><span class="identifier">pointer</span> <span class="identifier">new_connection</span> <span class="special">=</span>
  89       <span class="identifier">tcp_connection</span><span class="special">::</span><span class="identifier">create</span><span class="special">(</span><span class="identifier">acceptor_</span><span class="special">.</span><span class="identifier">get_io_service</span><span class="special">());</span>
  90
  91     <span class="identifier">acceptor_</span><span class="special">.</span><span class="identifier">async_accept</span><span class="special">(</span><span class="identifier">new_connection</span><span class="special">-&gt;</span><span class="identifier">socket</span><span class="special">(),</span>
  92         <span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(&amp;</span><span class="identifier">tcp_server</span><span class="special">::</span><span class="identifier">handle_accept</span><span class="special">,</span> <span class="keyword">this</span><span class="special">,</span> <span class="identifier">new_connection</span><span class="special">,</span>
  93           <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">placeholders</span><span class="special">::</span><span class="identifier">error</span><span class="special">));</span>
  94   <span class="special">}</span>
  95 </pre>
  96 <p>
  97         The function <code class="computeroutput"><span class="identifier">handle_accept</span><span class="special">()</span></code> is called when the asynchronous accept
  98         operation initiated by <code class="computeroutput"><span class="identifier">start_accept</span><span class="special">()</span></code> finishes. It services the client request,
  99         and then calls <code class="computeroutput"><span class="identifier">start_accept</span><span class="special">()</span></code> to initiate the next accept operation.
 100       </p>
 101 <pre class="programlisting">  <span class="keyword">void</span> <span class="identifier">handle_accept</span><span class="special">(</span><span class="identifier">tcp_connection</span><span class="special">::</span><span class="identifier">pointer</span> <span class="identifier">new_connection</span><span class="special">,</span>
 102       <span class="keyword">const</span> <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="special">&amp;</span> <span class="identifier">error</span><span class="special">)</span>
 103   <span class="special">{</span>
 104     <span class="keyword">if</span> <span class="special">(!</span><span class="identifier">error</span><span class="special">)</span>
 105     <span class="special">{</span>
 106       <span class="identifier">new_connection</span><span class="special">-&gt;</span><span class="identifier">start</span><span class="special">();</span>
 107     <span class="special">}</span>
 108
 109     <span class="identifier">start_accept</span><span class="special">();</span>
 110   <span class="special">}</span>
 111 </pre>
 112 <h5>
 113 <a name="boost_asio.tutorial.tutdaytime3.h2"></a>
 114         <span class="phrase"><a name="boost_asio.tutorial.tutdaytime3.the_tcp_connection_class"></a></span><a class="link" href="tutdaytime3.html#boost_asio.tutorial.tutdaytime3.the_tcp_connection_class">The tcp_connection
 115         class</a>
 116       </h5>
 117 <p>
 118         We will use <code class="computeroutput"><span class="identifier">shared_ptr</span></code> and
 119         <code class="computeroutput"><span class="identifier">enable_shared_from_this</span></code> because
 120         we want to keep the <code class="computeroutput"><span class="identifier">tcp_connection</span></code>
 121         object alive as long as there is an operation that refers to it.
 122       </p>
 123 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">tcp_connection</span>
 124   <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">enable_shared_from_this</span><span class="special">&lt;</span><span class="identifier">tcp_connection</span><span class="special">&gt;</span>
 125 <span class="special">{</span>
 126 <span class="keyword">public</span><span class="special">:</span>
 127   <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special">&lt;</span><span class="identifier">tcp_connection</span><span class="special">&gt;</span> <span class="identifier">pointer</span><span class="special">;</span>
 128
 129   <span class="keyword">static</span> <span class="identifier">pointer</span> <span class="identifier">create</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="special">&amp;</span> <span class="identifier">io_service</span><span class="special">)</span>
 130   <span class="special">{</span>
 131     <span class="keyword">return</span> <span class="identifier">pointer</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">tcp_connection</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">));</span>
 132   <span class="special">}</span>
 133
 134   <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">socket</span><span class="special">()</span>
 135   <span class="special">{</span>
 136     <span class="keyword">return</span> <span class="identifier">socket_</span><span class="special">;</span>
 137   <span class="special">}</span>
 138 </pre>
 139 <p>
 140         In the function <code class="computeroutput"><span class="identifier">start</span><span class="special">()</span></code>,
 141         we call boost::asio::async_write() to serve the data to the client. Note
 142         that we are using boost::asio::async_write(), rather than <a class="link" href="../reference/basic_stream_socket/async_write_some.html" title="basic_stream_socket::async_write_some">ip::tcp::socket::async_write_some()</a>,
 143         to ensure that the entire block of data is sent.
 144       </p>
 145 <pre class="programlisting">  <span class="keyword">void</span> <span class="identifier">start</span><span class="special">()</span>
 146   <span class="special">{</span>
 147 </pre>
 148 <p>
 149         The data to be sent is stored in the class member <code class="computeroutput"><span class="identifier">message_</span></code>
 150         as we need to keep the data valid until the asynchronous operation is complete.
 151       </p>
 152 <pre class="programlisting">    <span class="identifier">message_</span> <span class="special">=</span> <span class="identifier">make_daytime_string</span><span class="special">();</span>
 153 </pre>
 154 <p>
 155         When initiating the asynchronous operation, and if using boost::bind(), you
 156         must specify only the arguments that match the handler's parameter list.
 157         In this program, both of the argument placeholders (boost::asio::placeholders::error
 158         and boost::asio::placeholders::bytes_transferred) could potentially have
 159         been removed, since they are not being used in <code class="computeroutput"><span class="identifier">handle_write</span><span class="special">()</span></code>.
 160       </p>
 161 <pre class="programlisting">    <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">socket_</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">message_</span><span class="special">),</span>
 162         <span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(&amp;</span><span class="identifier">tcp_connection</span><span class="special">::</span><span class="identifier">handle_write</span><span class="special">,</span> <span class="identifier">shared_from_this</span><span class="special">(),</span>
 163           <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">placeholders</span><span class="special">::</span><span class="identifier">error</span><span class="special">,</span>
 164           <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">placeholders</span><span class="special">::</span><span class="identifier">bytes_transferred</span><span class="special">));</span>
 165 </pre>
 166 <p>
 167         Any further actions for this client connection are now the responsibility
 168         of <code class="computeroutput"><span class="identifier">handle_write</span><span class="special">()</span></code>.
 169       </p>
 170 <pre class="programlisting">  <span class="special">}</span>
 171
 172 <span class="keyword">private</span><span class="special">:</span>
 173   <span class="identifier">tcp_connection</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="special">&amp;</span> <span class="identifier">io_service</span><span class="special">)</span>
 174     <span class="special">:</span> <span class="identifier">socket_</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">)</span>
 175   <span class="special">{</span>
 176   <span class="special">}</span>
 177
 178   <span class="keyword">void</span> <span class="identifier">handle_write</span><span class="special">(</span><span class="keyword">const</span> <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="special">&amp;</span> <span class="comment">/*error*/</span><span class="special">,</span>
 179       <span class="identifier">size_t</span> <span class="comment">/*bytes_transferred*/</span><span class="special">)</span>
 180   <span class="special">{</span>
 181   <span class="special">}</span>
 182
 183   <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket_</span><span class="special">;</span>
 184   <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">message_</span><span class="special">;</span>
 185 <span class="special">};</span>
 186 </pre>
 187 <h5>
 188 <a name="boost_asio.tutorial.tutdaytime3.h3"></a>
 189         <span class="phrase"><a name="boost_asio.tutorial.tutdaytime3.removing_unused_handler_parameters"></a></span><a class="link" href="tutdaytime3.html#boost_asio.tutorial.tutdaytime3.removing_unused_handler_parameters">Removing
 190         unused handler parameters</a>
 191       </h5>
 192 <p>
 193         You may have noticed that the <code class="computeroutput"><span class="identifier">error</span></code>,
 194         and <code class="computeroutput"><span class="identifier">bytes_transferred</span></code> parameters
 195         are not used in the body of the <code class="computeroutput"><span class="identifier">handle_write</span><span class="special">()</span></code> function. If parameters are not needed,
 196         it is possible to remove them from the function so that it looks like:
 197       </p>
 198 <pre class="programlisting">  <span class="keyword">void</span> <span class="identifier">handle_write</span><span class="special">()</span>
 199   <span class="special">{</span>
 200   <span class="special">}</span>
 201 </pre>
 202 <p>
 203         The boost::asio::async_write() call used to initiate the call can then be
 204         changed to just:
 205       </p>
 206 <pre class="programlisting">  <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">socket_</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">message_</span><span class="special">),</span>
 207       <span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(&amp;</span><span class="identifier">tcp_connection</span><span class="special">::</span><span class="identifier">handle_write</span><span class="special">,</span> <span class="identifier">shared_from_this</span><span class="special">()));</span>
 208 </pre>
 209 <p>
 210         See the <a class="link" href="tutdaytime3/src.html" title="Source listing for Daytime.3">full source listing</a>
 211       </p>
 212 <p>
 213         Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a>
 214       </p>
 215 <p>
 216         Previous: <a class="link" href="tutdaytime2.html" title="Daytime.2 - A synchronous TCP daytime server">Daytime.2 - A synchronous
 217         TCP daytime server</a>
 218       </p>
 219 <p>
 220         Next: <a class="link" href="tutdaytime4.html" title="Daytime.4 - A synchronous UDP daytime client">Daytime.4 - A synchronous
 221         UDP daytime client</a>
 222       </p>
 223 </div>
 224 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 225 <td align="left"></td>
 226 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2017 Christopher M. Kohlhoff<p>
 227         Distributed under the Boost Software License, Version 1.0. (See accompanying
 228         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>)
 229       </p>
 230 </div></td>
 231 </tr></table>
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