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| 2 | <!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/src/tools/qthreadstorage_unix.cpp:163 -->
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| 20 | <font color="#004faf">Home</font></a>
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| 22 | <font color="#004faf">All Classes</font></a>
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| 24 | <font color="#004faf">Main Classes</font></a>
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| 31 | </td>
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| 32 | <td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QThreadStorage Class Reference</h1>
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| 33 |
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| 34 | <p>The QThreadStorage class provides per-thread data storage.
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| 35 | <a href="#details">More...</a>
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| 36 | <p>All the functions in this class are <a href="threads.html#threadsafe">thread-safe</a> when Qt is built with thread support.</p>
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| 37 | <p><tt>#include <<a href="qthreadstorage-h.html">qthreadstorage.h</a>></tt>
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| 38 | <p><a href="qthreadstorage-members.html">List of all member functions.</a>
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| 39 | <h2>Public Members</h2>
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| 40 | <ul>
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| 41 | <li class=fn><a href="#QThreadStorage"><b>QThreadStorage</b></a> ()</li>
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| 42 | <li class=fn><a href="#~QThreadStorage"><b>~QThreadStorage</b></a> ()</li>
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| 43 | <li class=fn>bool <a href="#hasLocalData"><b>hasLocalData</b></a> () const</li>
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| 44 | <li class=fn>T & <a href="#localData"><b>localData</b></a> ()</li>
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| 45 | <li class=fn>T <a href="#localData-2"><b>localData</b></a> () const</li>
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| 46 | <li class=fn>void <a href="#setLocalData"><b>setLocalData</b></a> ( T data )</li>
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| 47 | </ul>
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| 48 | <hr><a name="details"></a><h2>Detailed Description</h2>
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| 49 |
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| 50 |
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| 51 | The QThreadStorage class provides per-thread data storage.
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| 52 | <p>
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| 53 |
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| 54 |
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| 55 | <p> QThreadStorage is a template class that provides per-thread data
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| 56 | storage.
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| 57 | <p> <em>Note that due to compiler limitations, QThreadStorage can only store pointers.</em>
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| 58 | <p> The <a href="#setLocalData">setLocalData</a>() function stores a single thread-specific value
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| 59 | for the calling thread. The data can be accessed later using the
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| 60 | <a href="#localData">localData</a>() functions. QThreadStorage takes ownership of the
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| 61 | data (which must be created on the heap with <em>new</em>) and deletes
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| 62 | it when the thread exits (either normally or via termination).
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| 63 | <p> The <a href="#hasLocalData">hasLocalData</a>() function allows the programmer to determine if
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| 64 | data has previously been set using the setLocalData() function.
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| 65 | This is useful for lazy initializiation.
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| 66 | <p> For example, the following code uses QThreadStorage to store a
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| 67 | single cache for each thread that calls the <em>cacheObject()</em> and
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| 68 | <em>removeFromCache()</em> functions. The cache is automatically
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| 69 | deleted when the calling thread exits (either normally or via
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| 70 | termination).
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| 71 | <p> <pre>
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| 72 | QThreadStorage<QCache<SomeClass> *> caches;
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| 73 |
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| 74 | void cacheObject( const <a href="qstring.html">QString</a> &key, SomeClass *object )
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| 75 | {
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| 76 | if ( ! caches.hasLocalData() )
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| 77 | caches.setLocalData( new <a href="qcache.html">QCache</a><SomeClass> );
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| 78 |
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| 79 | caches.localData()->insert( key, object );
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| 80 | }
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| 81 |
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| 82 | void removeFromCache( const <a href="qstring.html">QString</a> &key )
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| 83 | {
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| 84 | if ( ! caches.hasLocalData() )
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| 85 | return; // nothing to do
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| 86 |
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| 87 | caches.localData()->remove( key );
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| 88 | }
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| 89 | </pre>
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| 90 |
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| 91 | <p> <h3> Caveats
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| 92 | </h3>
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| 93 | <a name="1"></a><p> <ul>
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| 94 | <p> <li> As noted above, QThreadStorage can only store pointers due to
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| 95 | compiler limitations. Support for value-based objects will be
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| 96 | added when the majority of compilers are able to support partial
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| 97 | template specialization.
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| 98 | <p> <li> The <a href="#~QThreadStorage">destructor</a> does <em>not</em>
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| 99 | delete per-thread data. QThreadStorage only deletes per-thread
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| 100 | data when the thread exits or when <a href="#setLocalData">setLocalData</a>() is called
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| 101 | multiple times.
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| 102 | <p> <li> QThreadStorage can only be used with threads started with
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| 103 | <a href="qthread.html">QThread</a>. It <em>cannot</em> be used with threads started with
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| 104 | platform-specific APIs.
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| 105 | <p> <li> As a corollary to the above, platform-specific APIs cannot be
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| 106 | used to exit or terminate a QThread using QThreadStorage. Doing so
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| 107 | will cause all per-thread data to be leaked. See <a href="qthread.html#exit">QThread::exit</a>()
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| 108 | and <a href="qthread.html#terminate">QThread::terminate</a>().
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| 109 | <p> <li> QThreadStorage <em>can</em> be used to store data for the <em>main()</em>
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| 110 | thread <em>after</em> <a href="qapplication.html">QApplication</a> has been constructed. QThreadStorage
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| 111 | deletes all data set for the <em>main()</em> thread when QApplication is
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| 112 | destroyed, regardless of whether or not the <em>main()</em> thread has
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| 113 | actually finished.
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| 114 | <p> <li> The implementation of QThreadStorage limits the total number of
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| 115 | QThreadStorage objects to 256. An unlimited number of threads
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| 116 | can store per-thread data in each QThreadStorage object.
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| 117 | <p> </ul>
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| 118 | <p>See also <a href="environment.html">Environment Classes</a> and <a href="thread.html">Threading</a>.
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| 119 |
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| 120 | <hr><h2>Member Function Documentation</h2>
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| 121 | <h3 class=fn><a name="QThreadStorage"></a>QThreadStorage::QThreadStorage ()
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| 122 | </h3>
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| 123 |
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| 124 | <p> Constructs a new per-thread data storage object.
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| 125 |
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| 126 | <h3 class=fn><a name="~QThreadStorage"></a>QThreadStorage::~QThreadStorage ()
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| 127 | </h3>
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| 128 |
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| 129 | <p> Destroys the per-thread data storage object.
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| 130 | <p> Note: The per-thread data stored is <em>not</em> deleted. Any data left
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| 131 | in QThreadStorage is leaked. Make sure that all threads using
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| 132 | QThreadStorage have exited before deleting the QThreadStorage.
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| 133 | <p> <p>See also <a href="#hasLocalData">hasLocalData</a>().
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| 134 |
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| 135 | <h3 class=fn>bool <a name="hasLocalData"></a>QThreadStorage::hasLocalData () const
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| 136 | </h3>
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| 137 |
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| 138 | <p> Returns TRUE if the calling thread has non-zero data available;
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| 139 | otherwise returns FALSE.
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| 140 | <p> <p>See also <a href="#localData">localData</a>().
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| 141 |
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| 142 | <h3 class=fn>T & <a name="localData"></a>QThreadStorage::localData ()
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| 143 | </h3>
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| 144 |
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| 145 | <p> Returns a reference to the data that was set by the calling
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| 146 | thread.
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| 147 | <p> Note: QThreadStorage can only store pointers. This function
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| 148 | returns a <em>reference</em> to the pointer that was set by the calling
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| 149 | thread. The value of this reference is 0 if no data was set by
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| 150 | the calling thread,
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| 151 | <p> <p>See also <a href="#hasLocalData">hasLocalData</a>().
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| 152 |
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| 153 | <h3 class=fn>T <a name="localData-2"></a>QThreadStorage::localData () const
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| 154 | </h3>
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| 155 |
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| 156 | This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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| 157 | <p> Returns a copy of the data that was set by the calling thread.
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| 158 | <p> Note: QThreadStorage can only store pointers. This function
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| 159 | returns a pointer to the data that was set by the calling thread.
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| 160 | If no data was set by the calling thread, this function returns 0.
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| 161 | <p> <p>See also <a href="#hasLocalData">hasLocalData</a>().
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| 162 |
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| 163 | <h3 class=fn>void <a name="setLocalData"></a>QThreadStorage::setLocalData ( T data )
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| 164 | </h3>
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| 165 |
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| 166 | <p> Sets the local data for the calling thread to <em>data</em>. It can be
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| 167 | accessed later using the <a href="#localData">localData</a>() functions.
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| 168 | <p> If <em>data</em> is 0, this function deletes the previous data (if
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| 169 | any) and returns immediately.
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| 170 | <p> If <em>data</em> is non-zero, QThreadStorage takes ownership of the <em>data</em> and deletes it automatically either when the thread exits
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| 171 | (either normally or via termination) or when <a href="#setLocalData">setLocalData</a>() is
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| 172 | called again.
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| 173 | <p> Note: QThreadStorage can only store pointers. The <em>data</em>
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| 174 | argument must be either a pointer to an object created on the heap
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| 175 | (i.e. using <em>new</em>) or 0. You should not delete <em>data</em>
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| 176 | yourself; QThreadStorage takes ownership and will delete the <em>data</em> itself.
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| 177 | <p> <p>See also <a href="#localData">localData</a>() and <a href="#hasLocalData">hasLocalData</a>().
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| 178 |
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| 179 | <!-- eof -->
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| 180 | <hr><p>
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| 181 | This file is part of the <a href="index.html">Qt toolkit</a>.
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| 182 | Copyright © 1995-2007
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| 183 | <a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
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| 184 | <table width=100% cellspacing=0 border=0><tr>
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| 185 | <td>Copyright © 2007
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| 186 | <a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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| 187 | <td align=right><div align=right>Qt 3.3.8</div>
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| 188 | </table></div></address></body>
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| 189 | </html>
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