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The QGuardedPtr class is a template class that provides guarded pointers to QObjects. More...
#include <qguardedptr.h>
A guarded pointer, QGuardedPtr<X>, behaves like a normal C++ pointer X*, except that it is automatically set to 0 when the referenced object is destroyed (unlike normal C++ pointers, which become "dangling pointers" in such cases). X must be a subclass of QObject.
Guarded pointers are useful whenever you need to store a pointer to a QObject that is owned by someone else and therefore might be destroyed while you still hold a reference to it. You can safely test the pointer for validity.
Example:
QGuardedPtr<QLabel> label = new QLabel( 0, "label" ); label->setText( "I like guarded pointers" ); delete (QLabel*) label; // simulate somebody destroying the label if ( label) label->show(); else qDebug("The label has been destroyed");
The program will output The label has been destroyed rather than dereferencing an invalid address in label->show().
The functions and operators available with a QGuardedPtr are the same as those available with a normal unguarded pointer, except the pointer arithmetic operators (++, --, -, and +), which are normally used only with arrays of objects. Use them like normal pointers and you will not need to read this class documentation.
For creating guarded pointers, you can construct or assign to them from an X* or from another guarded pointer of the same type. You can compare them with each other using operator==() and operator!=(), or test for 0 with isNull(). And you can dereference them using either the *x or the x->member notation.
A guarded pointer will automatically cast to an X*, so you can
freely mix guarded and unguarded pointers. This means that if you
have a QGuardedPtr Note again that class X must inherit QObject, or a compilation
or link error will result.
See also Object Model.
Constructs a 0 guarded pointer.
See also isNull().
Constructs a guarded pointer that points to same object as p
points to.
Copy one guarded pointer from another. The constructed guarded
pointer points to the same object that p points to (which may
be 0).
Destroys the guarded pointer. Just like a normal pointer,
destroying a guarded pointer does not destroy the object being
pointed to.
Returns TRUE if the referenced object has been destroyed or if
there is no referenced object; otherwise returns FALSE.
Cast operator; implements pointer semantics. Because of this
function you can pass a QGuardedPtr<X> to a function where an X*
is required.
Inequality operator; implements pointer semantics, the negation of
operator==(). Returns TRUE if p and this guarded pointer are
not pointing to the same object; otherwise returns FALSE.
Dereference operator; implements pointer semantics. Just use this
operator as you would with a normal C++ pointer.
Overloaded arrow operator; implements pointer semantics. Just use
this operator as you would with a normal C++ pointer.
Assignment operator. This guarded pointer then points to the same
object as p points to.
Assignment operator. This guarded pointer then points to the same
object as p points to.
Equality operator; implements traditional pointer semantics.
Returns TRUE if both p and this guarded pointer are 0, or if
both p and this pointer point to the same object; otherwise
returns FALSE.
See also operator!=().
This file is part of the Qt toolkit.
Copyright © 1995-2007
Trolltech. All Rights Reserved.Member Function Documentation
QGuardedPtr::QGuardedPtr ()
QGuardedPtr::QGuardedPtr ( T * p )
QGuardedPtr::QGuardedPtr ( const QGuardedPtr<T> & p )
QGuardedPtr::~QGuardedPtr ()
bool QGuardedPtr::isNull () const
QGuardedPtr::operator T * () const
bool QGuardedPtr::operator!= ( const QGuardedPtr<T> & p ) const
T & QGuardedPtr::operator* () const
T * QGuardedPtr::operator-> () const
QGuardedPtr<T> & QGuardedPtr::operator= ( const QGuardedPtr<T> & p )
QGuardedPtr<T> & QGuardedPtr::operator= ( T * p )
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
bool QGuardedPtr::operator== ( const QGuardedPtr<T> & p ) const
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