<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Timer.1 - Using a timer synchronously</title> <link rel="stylesheet" href="../../boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2"> <link rel="start" href="../../index.html" title="Asio"> <link rel="up" href="../tutorial.html" title="Tutorial"> <link rel="prev" href="../tutorial.html" title="Tutorial"> <link rel="next" href="tuttimer1/src.html" title="Source listing for Timer.1"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <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> <div class="spirit-nav"> <a accesskey="p" href="../tutorial.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="tuttimer1/src.html"><img src="../../next.png" alt="Next"></a> </div> <div class="section" lang="en"> <div class="titlepage"><div><div><h3 class="title"> <a name="asio.tutorial.tuttimer1"></a><a class="link" href="tuttimer1.html" title="Timer.1 - Using a timer synchronously">Timer.1 - Using a timer synchronously</a> </h3></div></div></div> <p> This tutorial program introduces asio by showing how to perform a blocking wait on a timer. </p> <p> We start by including the necessary header files. </p> <p> All of the asio classes can be used by simply including the <code class="computeroutput"><span class="string">"asio.hpp"</span></code> header file. </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">asio</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> </pre> <p> Since this example uses timers, we need to include the appropriate Boost.Date_Time header file for manipulating times. </p> <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">date_time</span><span class="special">/</span><span class="identifier">posix_time</span><span class="special">/</span><span class="identifier">posix_time</span><span class="special">.</span><span class="identifier">hpp</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. This class provides access to I/O functionality. We declare an object of this type first thing in the main function. </p> <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span> <span class="identifier">io</span><span class="special">;</span> </pre> <p> Next we declare an object of type asio::deadline_timer. The core asio classes that provide I/O functionality (or as in this case timer functionality) always take a reference to an io_service as their first constructor argument. The second argument to the constructor sets the timer to expire 5 seconds from now. </p> <pre class="programlisting"> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">deadline_timer</span> <span class="identifier">t</span><span class="special">(</span><span class="identifier">io</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">posix_time</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">5</span><span class="special">));</span> </pre> <p> In this simple example we perform a blocking wait on the timer. That is, the call to <a class="link" href="../reference/basic_deadline_timer/wait.html" title="basic_deadline_timer::wait">deadline_timer::wait()</a> will not return until the timer has expired, 5 seconds after it was created (i.e. not from when the wait starts). </p> <p> A deadline timer is always in one of two states: "expired" or "not expired". If the <a class="link" href="../reference/basic_deadline_timer/wait.html" title="basic_deadline_timer::wait">deadline_timer::wait()</a> function is called on an expired timer, it will return immediately. </p> <pre class="programlisting"> <span class="identifier">t</span><span class="special">.</span><span class="identifier">wait</span><span class="special">();</span> </pre> <p> Finally we print the obligatory <code class="computeroutput"><span class="string">"Hello, world!"</span></code> message to show when the timer has expired. </p> <pre class="programlisting"> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Hello, world!\n"</span><span class="special">;</span> <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> </pre> <p> See the <a class="link" href="tuttimer1/src.html" title="Source listing for Timer.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="tuttimer2.html" title="Timer.2 - Using a timer asynchronously">Timer.2 - Using a timer asynchronously</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 - 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> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="../tutorial.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="tuttimer1/src.html"><img src="../../next.png" alt="Next"></a> </div> </body> </html>