/******************************************************************************** Copyright (C) 1992-2006 Trolltech ASA. All rights reserved.**** This file is part of the QtCore module of the Qt Toolkit.**** This file may be used under the terms of the GNU General Public** License version 2.0 as published by the Free Software Foundation** and appearing in the file LICENSE.GPL included in the packaging of** this file.  Please review the following information to ensure GNU** General Public Licensing requirements will be met:** http://www.trolltech.com/products/qt/opensource.html**** If you are unsure which license is appropriate for your use, please** review the following information:** http://www.trolltech.com/products/qt/licensing.html or contact the** sales department at sales@trolltech.com.**** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.******************************************************************************//*!    \class QPointer    \brief The QPointer class is a template class that provides guarded pointers to QObjects.    \ingroup objectmodel    \mainclass    A guarded pointer, QPointer<T>, behaves like a normal C++    pointer \c{T *}, 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). \c T 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:    \quotefromfile snippets/pointer/pointer.cpp    \skipto QPointer<QLabel> label    \printuntil setText(    \dots    \printline if (label)    \printline show()    If the QLabel is deleted in the meantime, the \c label variable    will hold 0 instead of an invalid address, and the last line will    never be executed.    The functions and operators available with a QPointer are the    same as those available with a normal unguarded pointer, except    the pointer arithmetic operators (\c{+}, \c{-}, \c{++}, and    \c{--}), which are normally used only with arrays of objects.    Use QPointers 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 a T* 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(). You can dereference    them using either the \c *x or the \c x->member notation.    A guarded pointer will automatically cast to a \c T *, so you can    freely mix guarded and unguarded pointers. This means that if you    have a QPointer<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 QPointer as a parameter; just use    normal pointers. Use a QPointer when you are storing a pointer    over time.    Note that class \c T must inherit QObject, or a compilation or    link error will result.    \sa QObject, QObjectCleanupHandler*//*!    \fn QPointer::QPointer()    Constructs a 0 guarded pointer.    \sa isNull()*//*!    \fn QPointer::QPointer(T* p)    Constructs a guarded pointer that points to same object that \a p    points to.*//*!    \fn QPointer::QPointer(const QPointer<T> &p)    Copies one guarded pointer from another. The constructed guarded    pointer points to the same object that \a p points to (which may    be 0).*//*!    \fn QPointer::~QPointer()    Destroys the guarded pointer. Just like a normal pointer,    destroying a guarded pointer does \e not destroy the object being    pointed to.*//*!    \fn QPointer<T>& QPointer::operator=(const QPointer<T> &p)    Assignment operator. This guarded pointer will now point to the    same object that \a p points to.*//*!    \fn QPointer<T> & QPointer::operator=(T* p)    \overload    Assignment operator. This guarded pointer will now point to the    same object that \a p points to.*//*!    \fn bool QPointer::isNull() const    Returns \c true if the referenced object has been destroyed or if    there is no referenced object; otherwise returns false.*//*!    \fn T* QPointer::operator->() const    Overloaded arrow operator; implements pointer semantics. Just use    this operator as you would with a normal C++ pointer.*//*!    \fn T& QPointer::operator*() const    Dereference operator; implements pointer semantics. Just use this    operator as you would with a normal C++ pointer.*//*!    \fn QPointer::operator T*() const    Cast operator; implements pointer semantics. Because of this    function you can pass a QPointer\<T\> to a function where a T*    is required.*//*!    \fn bool operator==(const T *o, const QPointer<T> &p)    Equality operator. Returns true if \a o and the guarded    pointer \a p are pointing to the same object, otherwise    returns false.*//*!    \fn bool operator==(const QPointer<T> &p, const T *o)    Equality operator. Returns true if \a o and the guarded    pointer \a p are pointing to the same object, otherwise    returns false.*//*!    \fn bool operator==(T *o, const QPointer<T> &p)    Equality operator. Returns true if \a o and the guarded    pointer \a p are pointing to the same object, otherwise    returns false.*//*!    \fn bool operator==(const QPointer<T> &p, T *o)    Equality operator. Returns true if \a o and the guarded    pointer \a p are pointing to the same object, otherwise    returns false.*//*!    \fn bool operator==(const QPointer<T> &p1, const QPointer<T> &p2)    Equality operator. Returns true if the guarded pointers \a p1 and \a p2    are pointing to the same object, otherwise    returns false.*//*!    \fn bool operator!=(const T *o, const QPointer<T> &p)    Inequality operator. Returns true if \a o and the guarded    pointer \a p are not pointing to the same object, otherwise    returns false.*//*!    \fn bool operator!=(const QPointer<T> &p, const T *o)    Inequality operator. Returns true if \a o and the guarded    pointer \a p are not pointing to the same object, otherwise    returns false.*//*!    \fn bool operator!=(T *o, const QPointer<T> &p)    Inequality operator. Returns true if \a o and the guarded    pointer \a p are not pointing to the same object, otherwise    returns false.*//*!    \fn bool operator!=(const QPointer<T> &p, T *o)    Inequality operator. Returns true if \a o and the guarded    pointer \a p are not pointing to the same object, otherwise    returns false.*//*!    \fn bool operator!=(const QPointer<T> &p1, const QPointer<T> &p2)    Inequality operator. Returns true if  the guarded pointers \a p1 and    \a p2 are not pointing to the same object, otherwise    returns false.*/