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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 null when the referenced object is destroyed (unlike normal C++ pointers, which become "dangling pointers" in that case). 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 keep a reference to it. You can safely test the pointer for validity.
Example:
QGuardedPtr<QFrame> label = new QLabel( 0,"label" ); label->setText("I like guarded pointers"); delete (QLabel*) label; // emulate somebody destroying the label if ( label) label->show(); else qDebug("The label has been destroyed");
The program will output
The label has been destroyedrather 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 for equality (==) and inequality (!=), or test for null with isNull(). Finally, 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.
Constructs a null guarded pointer.
See also isNull().
Constructs a guarded pointer that points to same object as is
pointed to by p.
Copy one guarded pointer from another. The constructed guarded pointer
points to the same object that p pointed to (possibly null).
Destroys the guarded pointer.
Note that the object pointed to by the pointer
is not destructed, just as is the case with a normal unguarded pointer.
Returns TRUE if the referenced object has been destroyed or if there is
no referenced object.
Cast operator; implements pointer semantics. Because of this function
you can pass a QGuardedPtr Inequality operator; implements pointer semantics, the negation
of operator==.
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 does p.
Assignment operator. This guarded pointer then points to same object as is
pointed to by p.
Equality operator; implements traditional pointer semantics. Returns
TRUE if both p and this are null, or if both p and this point
to the same object.
See also operator!=().
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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 )
bool QGuardedPtr::operator== ( const QGuardedPtr<T> & p ) const
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