Adds asio library and Storage Module
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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<title>Daytime.3 - An asynchronous TCP daytime server</title>
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<link rel="stylesheet" href="../../boostbook.css" type="text/css">
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<meta name="generator" content="DocBook XSL Stylesheets V1.75.2">
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<link rel="home" href="../../index.html" title="Asio">
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<link rel="up" href="../tutorial.html" title="Tutorial">
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<link rel="prev" href="tutdaytime2/src.html" title="Source listing for Daytime.2">
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<link rel="next" href="tutdaytime3/src.html" title="Source listing for Daytime.3">
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</head>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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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>
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<hr>
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<div class="spirit-nav">
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<a accesskey="p" href="tutdaytime2/src.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.html"><img src="../../up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../home.png" alt="Home"></a><a accesskey="n" href="tutdaytime3/src.html"><img src="../../next.png" alt="Next"></a>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="asio.tutorial.tutdaytime3"></a><a class="link" href="tutdaytime3.html" title="Daytime.3 - An asynchronous TCP daytime server">Daytime.3 - An asynchronous
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TCP daytime server</a>
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</h3></div></div></div>
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<h5>
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<a name="asio.tutorial.tutdaytime3.h0"></a>
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<span><a name="asio.tutorial.tutdaytime3.the_main___function"></a></span><a class="link" href="tutdaytime3.html#asio.tutorial.tutdaytime3.the_main___function">The
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main() function</a>
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</h5>
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<pre class="programlisting">int main()
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{
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try
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{
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</pre>
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<p>
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We need to create a server object to accept incoming client connections.
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The <a class="link" href="../reference/io_context.html" title="io_context">io_context</a> object provides
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I/O services, such as sockets, that the server object will use.
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</p>
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<pre class="programlisting"> asio::io_context io_context;
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tcp_server server(io_context);
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</pre>
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<p>
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Run the <a class="link" href="../reference/io_context.html" title="io_context">io_context</a> object
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so that it will perform asynchronous operations on your behalf.
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</p>
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<pre class="programlisting"> io_context.run();
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}
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catch (std::exception& e)
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{
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std::cerr << e.what() << std::endl;
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}
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return 0;
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}
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</pre>
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<h5>
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<a name="asio.tutorial.tutdaytime3.h1"></a>
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<span><a name="asio.tutorial.tutdaytime3.the_tcp_server_class"></a></span><a class="link" href="tutdaytime3.html#asio.tutorial.tutdaytime3.the_tcp_server_class">The
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tcp_server class</a>
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</h5>
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<pre class="programlisting">class tcp_server
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{
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public:
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</pre>
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<p>
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The constructor initialises an acceptor to listen on TCP port 13.
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</p>
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<pre class="programlisting"> tcp_server(asio::io_context& io_context)
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: io_context_(io_context),
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acceptor_(io_context, tcp::endpoint(tcp::v4(), 13))
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{
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start_accept();
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}
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private:
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</pre>
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<p>
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The function <code class="computeroutput">start_accept()</code> creates a socket and initiates an
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asynchronous accept operation to wait for a new connection.
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</p>
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<pre class="programlisting"> void start_accept()
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{
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tcp_connection::pointer new_connection =
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tcp_connection::create(io_context_);
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acceptor_.async_accept(new_connection->socket(),
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boost::bind(&tcp_server::handle_accept, this, new_connection,
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asio::placeholders::error));
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}
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</pre>
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<p>
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The function <code class="computeroutput">handle_accept()</code> is called when the asynchronous
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accept operation initiated by <code class="computeroutput">start_accept()</code> finishes. It services
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the client request, and then calls <code class="computeroutput">start_accept()</code> to initiate
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the next accept operation.
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</p>
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<pre class="programlisting"> void handle_accept(tcp_connection::pointer new_connection,
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const asio::error_code& error)
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{
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if (!error)
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{
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new_connection->start();
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}
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start_accept();
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}
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</pre>
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<h5>
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<a name="asio.tutorial.tutdaytime3.h2"></a>
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<span><a name="asio.tutorial.tutdaytime3.the_tcp_connection_class"></a></span><a class="link" href="tutdaytime3.html#asio.tutorial.tutdaytime3.the_tcp_connection_class">The
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tcp_connection class</a>
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</h5>
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<p>
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We will use <code class="computeroutput">shared_ptr</code> and <code class="computeroutput">enable_shared_from_this</code>
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because we want to keep the <code class="computeroutput">tcp_connection</code> object alive as long
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as there is an operation that refers to it.
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</p>
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<pre class="programlisting">class tcp_connection
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: public boost::enable_shared_from_this<tcp_connection>
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{
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public:
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typedef boost::shared_ptr<tcp_connection> pointer;
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static pointer create(asio::io_context& io_context)
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{
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return pointer(new tcp_connection(io_context));
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}
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tcp::socket& socket()
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{
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return socket_;
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}
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</pre>
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<p>
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In the function <code class="computeroutput">start()</code>, we call asio::async_write() to serve
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the data to the client. Note that we are using asio::async_write(), rather
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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>,
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to ensure that the entire block of data is sent.
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</p>
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<pre class="programlisting"> void start()
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{
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</pre>
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<p>
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The data to be sent is stored in the class member <code class="computeroutput">message_</code> as
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we need to keep the data valid until the asynchronous operation is complete.
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</p>
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<pre class="programlisting"> message_ = make_daytime_string();
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</pre>
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<p>
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When initiating the asynchronous operation, and if using <a class="link" href="boost_bind.html" title="boost::bind">boost::bind</a>
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, you must specify only the arguments that match the handler's parameter
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list. In this program, both of the argument placeholders (asio::placeholders::error
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and asio::placeholders::bytes_transferred) could potentially have been removed,
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since they are not being used in <code class="computeroutput">handle_write()</code>.
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</p>
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<pre class="programlisting"> asio::async_write(socket_, asio::buffer(message_),
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boost::bind(&tcp_connection::handle_write, shared_from_this(),
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asio::placeholders::error,
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asio::placeholders::bytes_transferred));
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</pre>
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<p>
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Any further actions for this client connection are now the responsibility
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of <code class="computeroutput">handle_write()</code>.
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</p>
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<pre class="programlisting"> }
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private:
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tcp_connection(asio::io_context& io_context)
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: socket_(io_context)
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{
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}
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void handle_write(const asio::error_code& /*error*/,
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size_t /*bytes_transferred*/)
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{
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}
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tcp::socket socket_;
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std::string message_;
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};
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</pre>
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<h5>
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<a name="asio.tutorial.tutdaytime3.h3"></a>
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<span><a name="asio.tutorial.tutdaytime3.removing_unused_handler_parameters"></a></span><a class="link" href="tutdaytime3.html#asio.tutorial.tutdaytime3.removing_unused_handler_parameters">Removing
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unused handler parameters</a>
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</h5>
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<p>
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You may have noticed that the <code class="computeroutput">error</code>, and <code class="computeroutput">bytes_transferred</code>
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parameters are not used in the body of the <code class="computeroutput">handle_write()</code> function.
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If parameters are not needed, it is possible to remove them from the function
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so that it looks like:
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</p>
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<pre class="programlisting"> void handle_write()
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{
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}
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</pre>
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<p>
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The asio::async_write() call used to initiate the call can then be changed
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to just:
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</p>
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<pre class="programlisting"> asio::async_write(socket_, asio::buffer(message_),
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boost::bind(&tcp_connection::handle_write, shared_from_this()));
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</pre>
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<p>
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See the <a class="link" href="tutdaytime3/src.html" title="Source listing for Daytime.3">full source listing</a>
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</p>
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<p>
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Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a>
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</p>
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<p>
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Previous: <a class="link" href="tutdaytime2.html" title="Daytime.2 - A synchronous TCP daytime server">Daytime.2 - A synchronous
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TCP daytime server</a>
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</p>
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<p>
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Next: <a class="link" href="tutdaytime4.html" title="Daytime.4 - A synchronous UDP daytime client">Daytime.4 - A synchronous
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UDP daytime client</a>
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</p>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M.
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Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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>)
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</p>
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</div></td>
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</tr></table>
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<hr>
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<div class="spirit-nav">
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<a accesskey="p" href="tutdaytime2/src.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.html"><img src="../../up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../home.png" alt="Home"></a><a accesskey="n" href="tutdaytime3/src.html"><img src="../../next.png" alt="Next"></a>
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</div>
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</body>
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</html>
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