Adds asio library and Storage Module

2020-12-01 22:41:04 +01:00
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+<html>
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+<title>Daytime.4 - A synchronous UDP daytime client</title>
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+<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>
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+</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">#include &lt;iostream&gt;
+#include &lt;boost/array.hpp&gt;
+#include &lt;asio.hpp&gt;
+
+using asio::ip::udp;
+</pre>
+<p>
+        The start of the application is essentially the same as for the TCP daytime
+        client.
+      </p>
+<pre class="programlisting">int main(int argc, char* argv[])
+{
+  try
+  {
+    if (argc != 2)
+    {
+      std::cerr &lt;&lt; "Usage: client &lt;host&gt;" &lt;&lt; std::endl;
+      return 1;
+    }
+
+    asio::io_context io_context;
+</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">    udp::resolver resolver(io_context);
+    udp::endpoint receiver_endpoint =
+      *resolver.resolve(udp::v4(), argv[1], "daytime").begin();
+</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">    udp::socket socket(io_context);
+    socket.open(udp::v4());
+
+    boost::array&lt;char, 1&gt; send_buf  = {{ 0 }};
+    socket.send_to(asio::buffer(send_buf), receiver_endpoint);
+</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">    boost::array&lt;char, 128&gt; recv_buf;
+    udp::endpoint sender_endpoint;
+    size_t len = socket.receive_from(
+        asio::buffer(recv_buf), sender_endpoint);
+
+    std::cout.write(recv_buf.data(), len);
+  }
+</pre>
+<p>
+        Finally, handle any exceptions that may have been thrown.
+      </p>
+<pre class="programlisting">  catch (std::exception&amp; e)
+  {
+    std::cerr &lt;&lt; e.what() &lt;&lt; std::endl;
+  }
+
+  return 0;
+}
+</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>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2020 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></td>
+</tr></table>
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