QGuardedPtr(3qt)QGuardedPtr(3qt)NAMEQGuardedPtr - Template class that provides guarded
pointers to QObjects
#include <qguardedptr.h>
Public Members
QGuardedPtr ()
QGuardedPtr ( T * p )
QGuardedPtr ( const QGuardedPtr<T> & p )
~QGuardedPtr ()
QGuardedPtr<T>& operator= ( const QGuardedPtr<T> & p )
QGuardedPtr<T>& operator= ( T * p )
bool operator== ( const QGuardedPtr<T> & p ) const
bool operator!= ( const QGuardedPtr<T> & p ) const
bool isNull () const
T* operator-> () const
T& operator* () const
operator T* ()const
DESCRIPTION
The QGuardedPtr class is a template class that provides
guarded pointers to QObjects
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 destroyed
rather than dereferencing an invalid address in
label->show().
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QGuardedPtr(3qt)QGuardedPtr(3qt)
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 only used 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<QWidget>, then you can pass
it to a function that requires a QWidget*. For this
reason, it is of little value to declare functions to take
a QGuardedPtr as a parameter - just use normal pointers.
Use a QGuardedPtr when you are storing a pointer over
time.
Note again that class X must inherit QObject or a
compilation or link error will result.
MEMBER FUNCTION DOCUMENTATIONQGuardedPtr::QGuardedPtr ()
Constructs a null guarded pointer.
See also isNull().
QGuardedPtr::QGuardedPtr ( T * p )
Constructs a guarded pointer that points to same object as
is pointed to by p.
QGuardedPtr::QGuardedPtr ( const QGuardedPtr<;T> & p )
Copy one guarded pointer from another. The constructed
guarded pointer points to the same object that p pointed
to (possibly null).
QGuardedPtr::~QGuardedPtr ()
Destructs 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.
QGuardedPtr::operator T* () const
Cast operator, implements pointer semantics. Because of
this function, you can pass a QGuardedPtr<X> to a function
where an X* is required.
bool QGuardedPtr::isNull () const
Returns TRUE if the referenced object has been destroyed
or if there is no referenced object.
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QGuardedPtr(3qt)QGuardedPtr(3qt)bool QGuardedPtr::operator!= ( const QGuardedPtr<T> & p ) const
Unequality operator, implements pointer semantics, the
negation of operator==().
T& QGuardedPtr::operator* () const
Dereference operator, implements pointer semantics. Just
use this operator as you would with a normal C++ pointer.
T* QGuardedPtr::operator-> () const
Overloaded arrow operator, implements pointer semantics.
Just use this operator as you would with a normal C++
pointer.
QGuardedPtr<;T> & QGuardedPtr::operator= ( T * p )
Assignment operator. This guarded pointer then points to
same object as is pointed to by p.
QGuardedPtr<;T>& QGuardedPtr::operator= ( const QGuardedPtr<T> & p
)
Assignment operator. This guarded pointer then points to
the same object as does p.
bool QGuardedPtr::operator== ( const QGuardedPtr<T> & p ) const
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!=().
SEE ALSO
http://doc.trolltech.com/qguardedptr.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2001 Trolltech AS,
http://www.trolltech.com. See the license file included
in the distribution for a complete license statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports
make our job much simpler. Thank you.
In case of content or formattting problems with this
manual page, please report them to qt-bugs@trolltech.com.
Please include the name of the manual page
(qguardedptr.3qt) and the Qt version (2.3.1).
Trolltech AS 13 June 2001 3
