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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the QtCore module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
** You may use this file in accordance with the terms and conditions
** contained in the either Technology Preview License Agreement or the
** Beta Release License Agreement.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain
** additional rights. These rights are described in the Nokia Qt LGPL
** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this
** package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 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 the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** If you are unsure which license is appropriate for your use, please
** contact the sales department at http://www.qtsoftware.com/contact.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\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.
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.
*/
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