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RedHat 9 (Linux i386) - man page for qguardedptr (redhat section 3qt)

QGuardedPtr(3qt)								 QGuardedPtr(3qt)

       QGuardedPtr - 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

       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 0 when the referenced object is destroyed (unlike normal C++
       pointers, which become "dangling pointers" in such cases). X must be a subclass of

       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.


	       QGuardedPtr<QLabel> label = new QLabel( 0, "label" );
	       label->setText( "I like guarded pointers" );
	       delete (QLabel*) label; // simulate somebody destroying the label
	       if ( label)
		   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<QWidget>, 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.

       See also Object Model.

QGuardedPtr::QGuardedPtr ()
       Constructs a 0 guarded pointer.

       See also isNull().

QGuardedPtr::QGuardedPtr ( T * p )
       Constructs a guarded pointer that points to same object as p points to.

QGuardedPtr::QGuardedPtr ( const QGuardedPtr<T> & p )
       Copy one guarded pointer from another. The constructed guarded pointer points to the same
       object that p points to (which may be 0).

QGuardedPtr::~QGuardedPtr ()
       Destroys the guarded pointer. Just like a normal pointer, destroying a guarded pointer
       does not destroy the object being pointed to.

bool QGuardedPtr::isNull () const
       Returns TRUE if the referenced object has been destroyed or if there is no referenced
       object; otherwise returns FALSE.

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::operator!= ( const QGuardedPtr<T> & p ) const
       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

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= ( const QGuardedPtr<T> & p )
       Assignment operator. This guarded pointer then points to the same object as p points to.

QGuardedPtr<;T> & QGuardedPtr::operator= ( T * p )
       This is an overloaded member function, provided for convenience. It behaves essentially
       like the above function.

       Assignment operator. This guarded pointer then points to the same object as p points to.

bool QGuardedPtr::operator== ( const QGuardedPtr<T> & p ) const
       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!=().

       http://doc.trolltech.com/qguardedptr.html http://www.trolltech.com/faq/tech.html

       Copyright 1992-2001 Trolltech AS, http://www.trolltech.com.  See the license file included
       in the distribution for a complete license statement.

       Generated automatically from the source code.

       If you find a bug in Qt, please report it as described in
       http://doc.trolltech.com/bughowto.html.	Good bug reports help us to help you. Thank you.

       The definitive Qt documentation is provided in HTML format; it is located at
       $QTDIR/doc/html and can be read using Qt Assistant or with a web browser. This man page is
       provided as a convenience for those users who prefer man pages, although this format is
       not officially supported by Trolltech.

       If you find errors in 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 (3.1.1).

Trolltech AS				 9 December 2002			 QGuardedPtr(3qt)

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