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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>QGuardedPtr Class Reference</h1>
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| 33 |
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| 34 | <p>The QGuardedPtr class is a template class that provides guarded pointers to QObjects.
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| 35 | <a href="#details">More...</a>
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| 36 | <p><tt>#include <<a href="qguardedptr-h.html">qguardedptr.h</a>></tt>
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| 37 | <p><a href="qguardedptr-members.html">List of all member functions.</a>
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| 38 | <h2>Public Members</h2>
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| 39 | <ul>
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| 40 | <li class=fn><a href="#QGuardedPtr"><b>QGuardedPtr</b></a> ()</li>
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| 41 | <li class=fn><a href="#QGuardedPtr-2"><b>QGuardedPtr</b></a> ( T * p )</li>
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| 42 | <li class=fn><a href="#QGuardedPtr-3"><b>QGuardedPtr</b></a> ( const QGuardedPtr<T> & p )</li>
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| 43 | <li class=fn><a href="#~QGuardedPtr"><b>~QGuardedPtr</b></a> ()</li>
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| 44 | <li class=fn>QGuardedPtr<T> & <a href="#operator-eq"><b>operator=</b></a> ( const QGuardedPtr<T> & p )</li>
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| 45 | <li class=fn>QGuardedPtr<T> & <a href="#operator-eq-2"><b>operator=</b></a> ( T * p )</li>
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| 46 | <li class=fn>bool <a href="#operator-eq-eq"><b>operator==</b></a> ( const QGuardedPtr<T> & p ) const</li>
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| 47 | <li class=fn>bool <a href="#operator!-eq"><b>operator!=</b></a> ( const QGuardedPtr<T> & p ) const</li>
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| 48 | <li class=fn>bool <a href="#isNull"><b>isNull</b></a> () const</li>
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| 49 | <li class=fn>T * <a href="#operator--gt"><b>operator-></b></a> () const</li>
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| 50 | <li class=fn>T & <a href="#operator*"><b>operator*</b></a> () const</li>
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| 51 | <li class=fn><a href="#operator-T-*"><b>operator T *</b></a> () const</li>
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| 52 | </ul>
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| 53 | <hr><a name="details"></a><h2>Detailed Description</h2>
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| 54 |
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| 55 |
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| 56 | The QGuardedPtr class is a template class that provides guarded pointers to QObjects.
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| 57 | <p>
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| 58 |
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| 59 | <p> A guarded pointer, <tt>QGuardedPtr<X></tt>, behaves like a normal C++
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| 60 | pointer <tt>X*</tt>, except that it is automatically set to 0 when
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| 61 | the referenced object is destroyed (unlike normal C++ pointers,
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| 62 | which become "dangling pointers" in such cases). <tt>X</tt> must be a
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| 63 | subclass of <a href="qobject.html">QObject</a>.
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| 64 | <p> Guarded pointers are useful whenever you need to store a pointer
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| 65 | to a QObject that is owned by someone else and therefore might be
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| 66 | destroyed while you still hold a reference to it. You can safely
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| 67 | test the pointer for validity.
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| 68 | <p> Example:
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| 69 | <pre>
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| 70 | QGuardedPtr<QLabel> label = new <a href="qlabel.html">QLabel</a>( 0, "label" );
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| 71 | label->setText( "I like guarded pointers" );
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| 72 |
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| 73 | delete (QLabel*) label; // simulate somebody destroying the label
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| 74 |
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| 75 | if ( label)
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| 76 | label->show();
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| 77 | else
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| 78 | <a href="qapplication.html#qDebug">qDebug</a>("The label has been destroyed");
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| 79 | </pre>
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| 80 |
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| 81 | <p> The program will output <tt>The label has been destroyed</tt> rather
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| 82 | than dereferencing an invalid address in <tt>label->show()</tt>.
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| 83 | <p> The functions and operators available with a QGuardedPtr are the
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| 84 | same as those available with a normal unguarded pointer, except
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| 85 | the pointer arithmetic operators (++, --, -, and +), which are
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| 86 | normally used only with arrays of objects. Use them like normal
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| 87 | pointers and you will not need to read this class documentation.
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| 88 | <p> For creating guarded pointers, you can construct or assign to them
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| 89 | from an X* or from another guarded pointer of the same type. You
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| 90 | can compare them with each other using <a href="#operator-eq-eq">operator==</a>() and
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| 91 | <a href="#operator!-eq">operator!=</a>(), or test for 0 with <a href="#isNull">isNull</a>(). And you can dereference
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| 92 | them using either the <tt>*x</tt> or the <tt>x->member</tt> notation.
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| 93 | <p> A guarded pointer will automatically cast to an X*, so you can
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| 94 | freely mix guarded and unguarded pointers. This means that if you
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| 95 | have a QGuardedPtr<QWidget>, you can pass it to a function that
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| 96 | requires a <a href="qwidget.html">QWidget</a>*. For this reason, it is of little value to
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| 97 | declare functions to take a QGuardedPtr as a parameter; just use
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| 98 | normal pointers. Use a QGuardedPtr when you are storing a pointer
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| 99 | over time.
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| 100 | <p> Note again that class <em>X</em> must inherit <a href="qobject.html">QObject</a>, or a compilation
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| 101 | or link error will result.
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| 102 | <p>See also <a href="objectmodel.html">Object Model</a>.
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| 103 |
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| 104 | <hr><h2>Member Function Documentation</h2>
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| 105 | <h3 class=fn><a name="QGuardedPtr"></a>QGuardedPtr::QGuardedPtr ()
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| 106 | </h3>
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| 107 |
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| 108 | <p> Constructs a 0 guarded pointer.
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| 109 | <p> <p>See also <a href="#isNull">isNull</a>().
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| 110 |
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| 111 | <h3 class=fn><a name="QGuardedPtr-2"></a>QGuardedPtr::QGuardedPtr ( T * p )
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| 112 | </h3>
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| 113 |
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| 114 | <p> Constructs a guarded pointer that points to same object as <em>p</em>
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| 115 | points to.
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| 116 |
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| 117 | <h3 class=fn><a name="QGuardedPtr-3"></a>QGuardedPtr::QGuardedPtr ( const <a href="qguardedptr.html">QGuardedPtr</a><T> & p )
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| 118 | </h3>
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| 119 |
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| 120 | <p> Copy one guarded pointer from another. The constructed guarded
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| 121 | pointer points to the same object that <em>p</em> points to (which may
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| 122 | be 0).
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| 123 |
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| 124 | <h3 class=fn><a name="~QGuardedPtr"></a>QGuardedPtr::~QGuardedPtr ()
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| 125 | </h3>
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| 126 |
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| 127 | <p> Destroys the guarded pointer. Just like a normal pointer,
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| 128 | destroying a guarded pointer does <em>not</em> destroy the object being
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| 129 | pointed to.
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| 130 |
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| 131 | <h3 class=fn>bool <a name="isNull"></a>QGuardedPtr::isNull () const
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| 132 | </h3>
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| 133 |
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| 134 | <p> Returns <tt>TRUE</tt> if the referenced object has been destroyed or if
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| 135 | there is no referenced object; otherwise returns FALSE.
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| 136 |
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| 137 | <h3 class=fn><a name="operator-T-*"></a>QGuardedPtr::operator T * () const
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| 138 | </h3>
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| 139 |
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| 140 | <p> Cast operator; implements pointer semantics. Because of this
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| 141 | function you can pass a QGuardedPtr<X> to a function where an X*
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| 142 | is required.
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| 143 |
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| 144 | <h3 class=fn>bool <a name="operator!-eq"></a>QGuardedPtr::operator!= ( const <a href="qguardedptr.html">QGuardedPtr</a><T> & p ) const
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| 145 | </h3>
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| 146 |
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| 147 | <p> Inequality operator; implements pointer semantics, the negation of
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| 148 | <a href="#operator-eq-eq">operator==</a>(). Returns TRUE if <em>p</em> and this guarded pointer are
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| 149 | not pointing to the same object; otherwise returns FALSE.
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| 150 |
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| 151 | <h3 class=fn>T & <a name="operator*"></a>QGuardedPtr::operator* () const
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| 152 | </h3>
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| 153 |
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| 154 | <p> Dereference operator; implements pointer semantics. Just use this
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| 155 | operator as you would with a normal C++ pointer.
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| 156 |
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| 157 | <h3 class=fn>T * <a name="operator--gt"></a>QGuardedPtr::operator-> () const
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| 158 | </h3>
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| 159 |
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| 160 | <p> Overloaded arrow operator; implements pointer semantics. Just use
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| 161 | this operator as you would with a normal C++ pointer.
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| 162 |
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| 163 | <h3 class=fn><a href="qguardedptr.html">QGuardedPtr</a><T> & <a name="operator-eq"></a>QGuardedPtr::operator= ( const <a href="qguardedptr.html">QGuardedPtr</a><T> & p )
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| 164 | </h3>
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| 165 |
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| 166 | <p> Assignment operator. This guarded pointer then points to the same
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| 167 | object as <em>p</em> points to.
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| 168 |
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| 169 | <h3 class=fn><a href="qguardedptr.html">QGuardedPtr</a><T> & <a name="operator-eq-2"></a>QGuardedPtr::operator= ( T * p )
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| 170 | </h3>
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| 171 | This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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| 172 | <p> Assignment operator. This guarded pointer then points to the same
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| 173 | object as <em>p</em> points to.
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| 174 |
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| 175 | <h3 class=fn>bool <a name="operator-eq-eq"></a>QGuardedPtr::operator== ( const <a href="qguardedptr.html">QGuardedPtr</a><T> & p ) const
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| 176 | </h3>
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| 177 |
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| 178 | <p> Equality operator; implements traditional pointer semantics.
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| 179 | Returns TRUE if both <em>p</em> and this guarded pointer are 0, or if
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| 180 | both <em>p</em> and this pointer point to the same object; otherwise
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| 181 | returns FALSE.
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| 182 | <p> <p>See also <a href="#operator!-eq">operator!=</a>().
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| 183 |
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| 184 | <!-- eof -->
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| 185 | <hr><p>
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| 186 | This file is part of the <a href="index.html">Qt toolkit</a>.
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| 187 | Copyright © 1995-2007
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| 188 | <a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
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| 189 | <table width=100% cellspacing=0 border=0><tr>
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| 190 | <td>Copyright © 2007
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| 191 | <a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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| 192 | <td align=right><div align=right>Qt 3.3.8</div>
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| 193 | </table></div></address></body>
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| 194 | </html>
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