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200 lines
9.7 KiB
200 lines
9.7 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/src/kernel/qtimer.cpp:42 -->
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>QTimer Class</title>
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<style type="text/css"><!--
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fn { margin-left: 1cm; text-indent: -1cm; }
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--></style>
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</head>
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<body>
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<table border="0" cellpadding="0" cellspacing="0" width="100%">
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<tr bgcolor="#E5E5E5">
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<td valign=center>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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<font color="#004faf">All Classes</font></a>
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<font color="#004faf">Main Classes</font></a>
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<font color="#004faf">Annotated</font></a>
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<font color="#004faf">Grouped Classes</font></a>
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<font color="#004faf">Functions</font></a>
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</td>
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QTimer Class Reference</h1>
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<p>The QTimer class provides timer signals and single-shot timers.
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<a href="#details">More...</a>
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<p><tt>#include <<a href="qtimer-h.html">qtimer.h</a>></tt>
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<p>Inherits <a href="qobject.html">QObject</a>.
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<p><a href="qtimer-members.html">List of all member functions.</a>
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<h2>Public Members</h2>
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<ul>
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<li class=fn><a href="#QTimer"><b>QTimer</b></a> ( QObject * parent = 0, const char * name = 0 )</li>
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<li class=fn><a href="#~QTimer"><b>~QTimer</b></a> ()</li>
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<li class=fn>bool <a href="#isActive"><b>isActive</b></a> () const</li>
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<li class=fn>int <a href="#start"><b>start</b></a> ( int msec, bool sshot = FALSE )</li>
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<li class=fn>void <a href="#changeInterval"><b>changeInterval</b></a> ( int msec )</li>
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<li class=fn>void <a href="#stop"><b>stop</b></a> ()</li>
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<li class=fn>int <a href="#timerId"><b>timerId</b></a> () const</li>
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</ul>
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<h2>Signals</h2>
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<ul>
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<li class=fn>void <a href="#timeout"><b>timeout</b></a> ()</li>
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</ul>
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<h2>Static Public Members</h2>
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<ul>
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<li class=fn>void <a href="#singleShot"><b>singleShot</b></a> ( int msec, QObject * receiver, const char * member )</li>
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</ul>
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<hr><a name="details"></a><h2>Detailed Description</h2>
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The QTimer class provides timer signals and single-shot timers.
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<p>
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<p> It uses <a href="qtimerevent.html">timer events</a> internally to
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provide a more versatile timer. QTimer is very easy to use:
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create a QTimer, call <a href="#start">start</a>() to start it and connect its
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<a href="#timeout">timeout</a>() to the appropriate slots. When the time is up it will
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emit the timeout() signal.
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<p> Note that a QTimer object is destroyed automatically when its
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parent object is destroyed.
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<p> Example:
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<pre>
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QTimer *timer = new QTimer( myObject );
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<a href="qobject.html#connect">connect</a>( timer, SIGNAL(<a href="#timeout">timeout</a>()), myObject, SLOT(timerDone()) );
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timer-><a href="#start">start</a>( 2000, TRUE ); // 2 seconds single-shot timer
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</pre>
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<p> You can also use the static <a href="#singleShot">singleShot</a>() function to create a
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single shot timer.
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<p> As a special case, a QTimer with timeout 0 times out as soon as
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all the events in the window system's event queue have been
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processed.
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<p> This can be used to do heavy work while providing a snappy
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user interface:
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<pre>
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QTimer *t = new QTimer( myObject );
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<a href="qobject.html#connect">connect</a>( t, SIGNAL(<a href="#timeout">timeout</a>()), SLOT(processOneThing()) );
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t-><a href="#start">start</a>( 0, FALSE );
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</pre>
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<p> myObject->processOneThing() will be called repeatedly and should
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return quickly (typically after processing one data item) so that
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Qt can deliver events to widgets and stop the timer as soon as it
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has done all its work. This is the traditional way of
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implementing heavy work in GUI applications; multi-threading is
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now becoming available on more and more platforms, and we expect
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that null events will eventually be replaced by threading.
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<p> Note that QTimer's accuracy depends on the underlying operating
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system and hardware. Most platforms support an accuracy of 20ms;
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some provide more. If Qt is unable to deliver the requested
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number of timer clicks, it will silently discard some.
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<p> An alternative to using QTimer is to call <a href="qobject.html#startTimer">QObject::startTimer</a>()
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for your object and reimplement the <a href="qobject.html#timerEvent">QObject::timerEvent</a>() event
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handler in your class (which must, of course, inherit <a href="qobject.html">QObject</a>).
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The disadvantage is that <a href="qobject.html#timerEvent">timerEvent</a>() does not support such
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high-level features as single-shot timers or signals.
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<p> Some operating systems limit the number of timers that may be
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used; Qt tries to work around these limitations.
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<p>See also <a href="events.html">Event Classes</a> and <a href="time.html">Time and Date</a>.
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<hr><h2>Member Function Documentation</h2>
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<h3 class=fn><a name="QTimer"></a>QTimer::QTimer ( <a href="qobject.html">QObject</a> * parent = 0, const char * name = 0 )
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</h3>
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Constructs a timer called <em>name</em>, with the parent <em>parent</em>.
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<p> Note that the parent object's destructor will destroy this timer
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object.
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<h3 class=fn><a name="~QTimer"></a>QTimer::~QTimer ()
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</h3>
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Destroys the timer.
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<h3 class=fn>void <a name="changeInterval"></a>QTimer::changeInterval ( int msec )
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</h3>
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Changes the timeout interval to <em>msec</em> milliseconds.
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<p> If the timer signal is pending, it will be stopped and restarted;
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otherwise it will be started.
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<p> <p>See also <a href="#start">start</a>() and <a href="#isActive">isActive</a>().
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<h3 class=fn>bool <a name="isActive"></a>QTimer::isActive () const
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</h3>
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<p> Returns TRUE if the timer is running (pending); otherwise returns
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FALSE.
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<p>Example: <a href="tutorial1-11.html#x2376">t11/cannon.cpp</a>.
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<h3 class=fn>void <a name="singleShot"></a>QTimer::singleShot ( int msec, <a href="qobject.html">QObject</a> * receiver, const char * member )<tt> [static]</tt>
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</h3>
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This static function calls a slot after a given time interval.
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<p> It is very convenient to use this function because you do not need
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to bother with a <a href="qobject.html#timerEvent">timerEvent</a> or
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to create a local QTimer object.
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<p> Example:
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<pre>
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#include <<a href="qapplication-h.html">qapplication.h</a>>
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#include <<a href="qtimer-h.html">qtimer.h</a>>
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int main( int argc, char **argv )
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{
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<a href="qapplication.html">QApplication</a> a( argc, argv );
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QTimer::<a href="#singleShot">singleShot</a>( 10*60*1000, &a, SLOT(<a href="qapplication.html#quit">quit</a>()) );
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... // create and show your widgets
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return a.<a href="qapplication.html#exec">exec</a>();
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}
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</pre>
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<p> This sample program automatically terminates after 10 minutes (i.e.
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600000 milliseconds).
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<p> The <em>receiver</em> is the receiving object and the <em>member</em> is the
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slot. The time interval is <em>msec</em>.
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<h3 class=fn>int <a name="start"></a>QTimer::start ( int msec, bool sshot = FALSE )
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</h3>
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Starts the timer with a <em>msec</em> milliseconds timeout, and returns
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the ID of the timer, or zero when starting the timer failed.
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<p> If <em>sshot</em> is TRUE, the timer will be activated only once;
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otherwise it will continue until it is stopped.
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<p> Any pending timer will be stopped.
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<p> <p>See also <a href="#singleShot">singleShot</a>(), <a href="#stop">stop</a>(), <a href="#changeInterval">changeInterval</a>(), and <a href="#isActive">isActive</a>().
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<p>Examples: <a href="aclock-example.html#x1204">aclock/aclock.cpp</a>, <a href="dirview-example.html#x1704">dirview/dirview.cpp</a>, <a href="distributor-example.html#x2671">distributor/distributor.ui.h</a>, <a href="forever-example.html#x1053">forever/forever.cpp</a>, <a href="hello-example.html#x1639">hello/hello.cpp</a>, <a href="tutorial1-11.html#x2377">t11/cannon.cpp</a>, and <a href="tutorial1-13.html#x2407">t13/cannon.cpp</a>.
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<h3 class=fn>void <a name="stop"></a>QTimer::stop ()
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</h3>
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Stops the timer.
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<p> <p>See also <a href="#start">start</a>().
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<p>Examples: <a href="dirview-example.html#x1705">dirview/dirview.cpp</a>, <a href="tutorial1-11.html#x2378">t11/cannon.cpp</a>, <a href="tutorial1-12.html#x2400">t12/cannon.cpp</a>, and <a href="tutorial1-13.html#x2408">t13/cannon.cpp</a>.
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<h3 class=fn>void <a name="timeout"></a>QTimer::timeout ()<tt> [signal]</tt>
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</h3>
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<p> This signal is emitted when the timer is activated.
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<p>Examples: <a href="aclock-example.html#x1205">aclock/aclock.cpp</a>, <a href="dirview-example.html#x1706">dirview/dirview.cpp</a>, <a href="distributor-example.html#x2672">distributor/distributor.ui.h</a>, <a href="forever-example.html#x1054">forever/forever.cpp</a>, <a href="hello-example.html#x1640">hello/hello.cpp</a>, and <a href="tutorial1-11.html#x2379">t11/cannon.cpp</a>.
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<h3 class=fn>int <a name="timerId"></a>QTimer::timerId () const
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</h3>
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<p> Returns the ID of the timer if the timer is running; otherwise returns
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-1.
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<!-- eof -->
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<hr><p>
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This file is part of the <a href="index.html">Qt toolkit</a>.
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Copyright © 1995-2007
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<a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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