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<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">#include &lt;iostream&gt;
#include &lt;boost/array.hpp&gt;
#include &lt;boost/asio.hpp&gt;
using boost::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;
}
boost::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(boost::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(
boost::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>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 Christopher
M. Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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