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QPointer< T > Class Template Reference

List of all members.


Detailed Description

template<class T>
class QPointer< T >

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

A guarded pointer, QPointer<T>, behaves like a normal C++ pointer {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). 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:

snippets/pointer/pointer.cpp QPointer<QLabel> label setText( if (label) show()

If the QLabel is deleted in the meantime, the 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 ({+}, {-}, {++}, and {--}), 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 *x or the x->member notation.

A guarded pointer will automatically cast to a 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 T must inherit QObject, or a compilation or link error will result.

See also:
QObject, QObjectCleanupHandler

Definition at line 34 of file qpointer.h.


Public Member Functions

bool isNull () const
 operator T * () const
T & operator* () const
T * operator-> () const
QPointer< T > & operator= (T *p)
QPointer< T > & operator= (const QPointer< T > &p)
 QPointer (const QPointer< T > &p)
 QPointer (T *p)
 QPointer ()
 ~QPointer ()

Private Attributes

QObjecto

The documentation for this class was generated from the following files:

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