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/*!

    \class QPointer

    \brief The QPointer class is a template class that provides guarded pointers to QObjects.

    \ingroup objectmodel

    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.

    Qt also provides QSharedPointer, an implementation of a reference-counted

    shared pointer object, which can be used to maintain a collection of

    references to an individual pointer.

    Example:

    \snippet doc/src/snippets/pointer/pointer.cpp 0

    \dots

    \snippet doc/src/snippets/pointer/pointer.cpp 1

    \snippet doc/src/snippets/pointer/pointer.cpp 2

    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 QSharedPointer, 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)

    Assignment operator. This guarded pointer will now point to the

    same object that \a p points to.

*/

/*!

    \fn T* QPointer::data() const

    \since 4.4

    Returns the pointer to the object being guarded.

*/

/*!

    \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.

*/