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| <div class="titlepage"><div><div><h3 class="title"> |
| <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 |
| TCP daytime client</a> |
| </h3></div></div></div> |
| <p> |
| This tutorial program shows how to use asio to implement a client application |
| with TCP. |
| </p> |
| <p> |
| We start by including the necessary header files. |
| </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> |
| </pre> |
| <p> |
| The purpose of this application is to access a daytime service, so we need |
| the user to specify the server. |
| </p> |
| <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> |
| |
| <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> |
| </pre> |
| <p> |
| 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> |
| object. |
| </p> |
| <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> |
| </pre> |
| <p> |
| We need to turn the server name that was specified as a parameter to the |
| 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> |
| object. |
| </p> |
| <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> |
| </pre> |
| <p> |
| A resolver takes a query object and turns it into a list of endpoints. We |
| 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 |
| <code class="computeroutput"><span class="string">"daytime"</span></code>. |
| </p> |
| <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> |
| </pre> |
| <p> |
| 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>. |
| A default constructed <a class="link" href="../reference/ip__basic_resolver/iterator.html" title="ip::basic_resolver::iterator">ip::tcp::resolver::iterator</a> |
| object is used as the end iterator. |
| </p> |
| <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> |
| <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">end</span><span class="special">;</span> |
| </pre> |
| <p> |
| Now we create and connect the socket. The list of endpoints obtained above |
| may contain both IPv4 and IPv6 endpoints, so we need to try each of them |
| until we find one that works. This keeps the client program independent of |
| a specific IP version. |
| </p> |
| <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> |
| <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> <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">host_not_found</span><span class="special">;</span> |
| <span class="keyword">while</span> <span class="special">(</span><span class="identifier">error</span> <span class="special">&&</span> <span class="identifier">endpoint_iterator</span> <span class="special">!=</span> <span class="identifier">end</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">socket</span><span class="special">.</span><span class="identifier">close</span><span class="special">();</span> |
| <span class="identifier">socket</span><span class="special">.</span><span class="identifier">connect</span><span class="special">(*</span><span class="identifier">endpoint_iterator</span><span class="special">++,</span> <span class="identifier">error</span><span class="special">);</span> |
| <span class="special">}</span> |
| <span class="keyword">if</span> <span class="special">(</span><span class="identifier">error</span><span class="special">)</span> |
| <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> |
| </pre> |
| <p> |
| The connection is open. All we need to do now is read the response from the |
| daytime service. |
| </p> |
| <p> |
| 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() |
| function automatically determines the size of the array to help prevent buffer |
| overruns. Instead of a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span></code>, |
| we could have used a <code class="computeroutput"><span class="keyword">char</span> <span class="special">[]</span></code> |
| or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span></code>. |
| </p> |
| <pre class="programlisting"> <span class="keyword">for</span> <span class="special">(;;)</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">128</span><span class="special">></span> <span class="identifier">buf</span><span class="special">;</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="identifier">error</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">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> |
| </pre> |
| <p> |
| 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> |
| function will exit with the boost::asio::error::eof error, which is how we |
| know to exit the loop. |
| </p> |
| <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> |
| <span class="keyword">break</span><span class="special">;</span> <span class="comment">// Connection closed cleanly by peer. |
| </span> <span class="keyword">else</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">error</span><span class="special">)</span> |
| <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> |
| <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> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| Finally, handle any exceptions that may have been thrown. |
| </p> |
| <pre class="programlisting"> <span class="special">}</span> |
| <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> |
| </pre> |
| <p> |
| See the <a class="link" href="tutdaytime1/src.html" title="Source listing for Daytime.1">full source listing</a> |
| </p> |
| <p> |
| Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a> |
| </p> |
| <p> |
| Next: <a class="link" href="tutdaytime2.html" title="Daytime.2 - A synchronous TCP daytime server">Daytime.2 - A synchronous |
| TCP daytime server</a> |
| </p> |
| </div> |
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| <td align="left"></td> |
| <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>) |
| </p> |
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