1QGuardedPtr(3qt) QGuardedPtr(3qt)
2
6 QGuardedPtr - Template class that provides guarded pointers to QObjects
7
9 #include <qguardedptr.h>
10 Public Members
12 QGuardedPtr ()
13 QGuardedPtr ( T * p )
14 QGuardedPtr ( const QGuardedPtr<T> & p )
15 ~QGuardedPtr ()
16 QGuardedPtr<T> & operator= ( const QGuardedPtr<T> & p )
17 QGuardedPtr<T> & operator= ( T * p )
18 bool operator== ( const QGuardedPtr<T> & p ) const
19 bool operator!= ( const QGuardedPtr<T> & p ) const
20 bool isNull () const
21 T * operator-> () const
22 T & operator* () const
23 operator T * () const
24
26 The QGuardedPtr class is a template class that provides guarded
27 pointers to QObjects.
28 A guarded pointer, QGuardedPtr<X>, behaves like a normal C++ pointer
30 X*, except that it is automatically set to 0 when the referenced object
31 is destroyed (unlike normal C++ pointers, which become "dangling
32 pointers" in such cases). X must be a subclass of QObject.
33 Guarded pointers are useful whenever you need to store a pointer to a
35 QObject that is owned by someone else and therefore might be destroyed
36 while you still hold a reference to it. You can safely test the pointer
37 for validity.
38 Example:
40 QGuardedPtr<QLabel> label = new QLabel( 0, "label" );
42 label->setText( "I like guarded pointers" );
43 delete (QLabel*) label; // simulate somebody destroying the label
44 if ( label)
45 label->show();
46 else
47 qDebug("The label has been destroyed");
48 The program will output The label has been destroyed rather than
50 dereferencing an invalid address in label->show().
51 The functions and operators available with a QGuardedPtr are the same
53 as those available with a normal unguarded pointer, except the pointer
54 arithmetic operators (++, --, -, and +), which are normally used only
55 with arrays of objects. Use them like normal pointers and you will not
56 need to read this class documentation.
57 For creating guarded pointers, you can construct or assign to them from
59 an X* or from another guarded pointer of the same type. You can compare
60 them with each other using operator==() and operator!=(), or test for 0
61 with isNull(). And you can dereference them using either the *x or the
62 x->member notation.
63 A guarded pointer will automatically cast to an X*, so you can freely
65 mix guarded and unguarded pointers. This means that if you have a
66 QGuardedPtr<QWidget>, you can pass it to a function that requires a
67 QWidget*. For this reason, it is of little value to declare functions
68 to take a QGuardedPtr as a parameter; just use normal pointers. Use a
69 QGuardedPtr when you are storing a pointer over time.
70 Note again that class X must inherit QObject, or a compilation or link
72 error will result.
73 See also Object Model.
75
78 Constructs a 0 guarded pointer.
79 See also isNull().
81
83 Constructs a guarded pointer that points to same object as p points to.
84
86 Copy one guarded pointer from another. The constructed guarded pointer
87 points to the same object that p points to (which may be 0).
88
90 Destroys the guarded pointer. Just like a normal pointer, destroying a
91 guarded pointer does not destroy the object being pointed to.
92
94 Returns TRUE if the referenced object has been destroyed or if there is
95 no referenced object; otherwise returns FALSE.
96
98 Cast operator; implements pointer semantics. Because of this function
99 you can pass a QGuardedPtr<X> to a function where an X* is required.
100
102 Inequality operator; implements pointer semantics, the negation of
103 operator==(). Returns TRUE if p and this guarded pointer are not
104 pointing to the same object; otherwise returns FALSE.
105
107 Dereference operator; implements pointer semantics. Just use this
108 operator as you would with a normal C++ pointer.
109
111 Overloaded arrow operator; implements pointer semantics. Just use this
112 operator as you would with a normal C++ pointer.
113
115 Assignment operator. This guarded pointer then points to the same
116 object as p points to.
117
119 This is an overloaded member function, provided for convenience. It
120 behaves essentially like the above function.
121 Assignment operator. This guarded pointer then points to the same
123 object as p points to.
124
126 Equality operator; implements traditional pointer semantics. Returns
127 TRUE if both p and this guarded pointer are 0, or if both p and this
128 pointer point to the same object; otherwise returns FALSE.
129 See also operator!=().
131
134 http://doc.trolltech.com/qguardedptr.html
135 http://www.trolltech.com/faq/tech.html
136
138 Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
139 license file included in the distribution for a complete license
140 statement.
141
143 Generated automatically from the source code.
144
146 If you find a bug in Qt, please report it as described in
147 http://doc.trolltech.com/bughowto.html. Good bug reports help us to
148 help you. Thank you.
149 The definitive Qt documentation is provided in HTML format; it is
151 located at $QTDIR/doc/html and can be read using Qt Assistant or with a
152 web browser. This man page is provided as a convenience for those users
153 who prefer man pages, although this format is not officially supported
154 by Trolltech.
155 If you find errors in this manual page, please report them to qt-
157 bugs@trolltech.com. Please include the name of the manual page
158 (qguardedptr.3qt) and the Qt version (3.3.8).
159Trolltech AS 2 February 2007 QGuardedPtr(3qt)