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These rights are described in the Trolltech GPL ** Exception version 1.0, which can be found at ** http://www.trolltech.com/products/qt/gplexception/ and in the file ** GPL_EXCEPTION.txt in this package. ** ** In addition, as a special exception, Trolltech, as the sole copyright ** holder for Qt Designer, grants users of the Qt/Eclipse Integration ** plug-in the right for the Qt/Eclipse Integration to link to ** functionality provided by Qt Designer and its related libraries. ** ** Trolltech reserves all rights not expressly granted herein. ** ** Trolltech ASA (c) 2007 ** ** 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, 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 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, 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 &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& QPointer::operator=(const QPointer &p) Assignment operator. This guarded pointer will now point to the same object that \a p points to. */ /*! \fn QPointer & 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\ to a function where a T* is required. */ /*! \fn bool operator==(const T *o, const QPointer &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 &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 &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 &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 &p1, const QPointer &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 &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 &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 &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 &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 &p1, const QPointer &p2) Inequality operator. Returns true if the guarded pointers \a p1 and \a p2 are not pointing to the same object, otherwise returns false. */