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195 lines
9.0 KiB
195 lines
9.0 KiB
13 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/qguardedptr.cpp:40 -->
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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>TQGuardedPtr Class</title>
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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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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>TQGuardedPtr Class Reference</h1>
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<p>The TQGuardedPtr class is a template class that provides guarded pointers to TQObjects.
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<a href="#details">More...</a>
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<p><tt>#include <<a href="qguardedptr-h.html">ntqguardedptr.h</a>></tt>
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<p><a href="qguardedptr-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="#TQGuardedPtr"><b>TQGuardedPtr</b></a> ()</li>
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<li class=fn><a href="#TQGuardedPtr-2"><b>TQGuardedPtr</b></a> ( T * p )</li>
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<li class=fn><a href="#TQGuardedPtr-3"><b>TQGuardedPtr</b></a> ( const TQGuardedPtr<T> & p )</li>
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<li class=fn><a href="#~TQGuardedPtr"><b>~TQGuardedPtr</b></a> ()</li>
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<li class=fn>TQGuardedPtr<T> & <a href="#operator-eq"><b>operator=</b></a> ( const TQGuardedPtr<T> & p )</li>
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<li class=fn>TQGuardedPtr<T> & <a href="#operator-eq-2"><b>operator=</b></a> ( T * p )</li>
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<li class=fn>bool <a href="#operator-eq-eq"><b>operator==</b></a> ( const TQGuardedPtr<T> & p ) const</li>
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<li class=fn>bool <a href="#operator!-eq"><b>operator!=</b></a> ( const TQGuardedPtr<T> & p ) const</li>
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<li class=fn>bool <a href="#isNull"><b>isNull</b></a> () const</li>
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<li class=fn>T * <a href="#operator--gt"><b>operator-></b></a> () const</li>
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<li class=fn>T & <a href="#operator*"><b>operator*</b></a> () const</li>
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<li class=fn><a href="#operator-T-*"><b>operator T *</b></a> () const</li>
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</ul>
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<hr><a name="details"></a><h2>Detailed Description</h2>
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The TQGuardedPtr class is a template class that provides guarded pointers to TQObjects.
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<p>
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<p> A guarded pointer, <tt>TQGuardedPtr<X></tt>, behaves like a normal C++
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pointer <tt>X*</tt>, except that it is automatically set to 0 when
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the referenced object is destroyed (unlike normal C++ pointers,
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which become "dangling pointers" in such cases). <tt>X</tt> must be a
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subclass of <a href="ntqobject.html">TQObject</a>.
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<p> Guarded pointers are useful whenever you need to store a pointer
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to a TQObject that is owned by someone else and therefore might be
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destroyed while you still hold a reference to it. You can safely
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test the pointer for validity.
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<p> Example:
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<pre>
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TQGuardedPtr<TQLabel> label = new <a href="ntqlabel.html">TQLabel</a>( 0, "label" );
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label->setText( "I like guarded pointers" );
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delete (TQLabel*) label; // simulate somebody destroying the label
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if ( label)
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label->show();
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else
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<a href="ntqapplication.html#qDebug">qDebug</a>("The label has been destroyed");
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</pre>
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<p> The program will output <tt>The label has been destroyed</tt> rather
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than dereferencing an invalid address in <tt>label->show()</tt>.
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<p> The functions and operators available with a TQGuardedPtr are the
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same as those available with a normal unguarded pointer, except
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the pointer arithmetic operators (++, --, -, and +), which are
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normally used only with arrays of objects. Use them like normal
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pointers and you will not need to read this class documentation.
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<p> For creating guarded pointers, you can construct or assign to them
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from an X* or from another guarded pointer of the same type. You
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can compare them with each other using <a href="#operator-eq-eq">operator==</a>() and
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<a href="#operator!-eq">operator!=</a>(), or test for 0 with <a href="#isNull">isNull</a>(). And you can dereference
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them using either the <tt>*x</tt> or the <tt>x->member</tt> notation.
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<p> A guarded pointer will automatically cast to an X*, so you can
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freely mix guarded and unguarded pointers. This means that if you
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have a TQGuardedPtr<TQWidget>, you can pass it to a function that
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requires a <a href="ntqwidget.html">TQWidget</a>*. For this reason, it is of little value to
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declare functions to take a TQGuardedPtr as a parameter; just use
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normal pointers. Use a TQGuardedPtr when you are storing a pointer
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over time.
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<p> Note again that class <em>X</em> must inherit <a href="ntqobject.html">TQObject</a>, or a compilation
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or link error will result.
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<p>See also <a href="objectmodel.html">Object Model</a>.
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<hr><h2>Member Function Documentation</h2>
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<h3 class=fn><a name="TQGuardedPtr"></a>TQGuardedPtr::TQGuardedPtr ()
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</h3>
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<p> Constructs a 0 guarded pointer.
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<p> <p>See also <a href="#isNull">isNull</a>().
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<h3 class=fn><a name="TQGuardedPtr-2"></a>TQGuardedPtr::TQGuardedPtr ( T * p )
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</h3>
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<p> Constructs a guarded pointer that points to same object as <em>p</em>
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points to.
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<h3 class=fn><a name="TQGuardedPtr-3"></a>TQGuardedPtr::TQGuardedPtr ( const <a href="ntqguardedptr.html">TQGuardedPtr</a><T> & p )
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</h3>
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<p> Copy one guarded pointer from another. The constructed guarded
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pointer points to the same object that <em>p</em> points to (which may
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be 0).
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<h3 class=fn><a name="~TQGuardedPtr"></a>TQGuardedPtr::~TQGuardedPtr ()
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</h3>
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<p> Destroys the guarded pointer. Just like a normal pointer,
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destroying a guarded pointer does <em>not</em> destroy the object being
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pointed to.
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<h3 class=fn>bool <a name="isNull"></a>TQGuardedPtr::isNull () const
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</h3>
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<p> Returns <tt>TRUE</tt> if the referenced object has been destroyed or if
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there is no referenced object; otherwise returns FALSE.
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<h3 class=fn><a name="operator-T-*"></a>TQGuardedPtr::operator T * () const
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</h3>
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<p> Cast operator; implements pointer semantics. Because of this
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function you can pass a TQGuardedPtr<X> to a function where an X*
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is required.
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<h3 class=fn>bool <a name="operator!-eq"></a>TQGuardedPtr::operator!= ( const <a href="ntqguardedptr.html">TQGuardedPtr</a><T> & p ) const
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</h3>
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<p> Inequality operator; implements pointer semantics, the negation of
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<a href="#operator-eq-eq">operator==</a>(). Returns TRUE if <em>p</em> and this guarded pointer are
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not pointing to the same object; otherwise returns FALSE.
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<h3 class=fn>T & <a name="operator*"></a>TQGuardedPtr::operator* () const
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</h3>
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<p> Dereference operator; implements pointer semantics. Just use this
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operator as you would with a normal C++ pointer.
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<h3 class=fn>T * <a name="operator--gt"></a>TQGuardedPtr::operator-> () const
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</h3>
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<p> Overloaded arrow operator; implements pointer semantics. Just use
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this operator as you would with a normal C++ pointer.
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<h3 class=fn><a href="ntqguardedptr.html">TQGuardedPtr</a><T> & <a name="operator-eq"></a>TQGuardedPtr::operator= ( const <a href="ntqguardedptr.html">TQGuardedPtr</a><T> & p )
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</h3>
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<p> Assignment operator. This guarded pointer then points to the same
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object as <em>p</em> points to.
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<h3 class=fn><a href="ntqguardedptr.html">TQGuardedPtr</a><T> & <a name="operator-eq-2"></a>TQGuardedPtr::operator= ( T * p )
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</h3>
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This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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<p> Assignment operator. This guarded pointer then points to the same
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object as <em>p</em> points to.
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<h3 class=fn>bool <a name="operator-eq-eq"></a>TQGuardedPtr::operator== ( const <a href="ntqguardedptr.html">TQGuardedPtr</a><T> & p ) const
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</h3>
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<p> Equality operator; implements traditional pointer semantics.
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Returns TRUE if both <em>p</em> and this guarded pointer are 0, or if
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both <em>p</em> and this pointer point to the same object; otherwise
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returns FALSE.
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<p> <p>See also <a href="#operator!-eq">operator!=</a>().
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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">TQt 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>TQt 3.3.8</div>
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</table></div></address></body>
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</html>
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