A guarded pointer, \fCQGuardedPtr<X>\fR, behaves like a normal C++ pointer \fCX*\fR, 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). \fCX\fR must be a subclass of TQObject.
Guarded pointers are useful whenever you need to store a pointer to a TQObject 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.
The program will output \fCThe label has been destroyed\fR rather than dereferencing an invalid address in \fClabel->show()\fR.
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The functions and operators available with a QGuardedPtr 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 them like normal pointers and you will not need to read this class documentation.
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For creating guarded pointers, you can construct or assign to them from an X* 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(). And you can dereference them using either the \fC*x\fR or the \fCx->member\fR notation.
A guarded pointer will automatically cast to an X*, so you can freely mix guarded and unguarded pointers. This means that if you have a QGuardedPtr<TQWidget>, you can pass it to a function that requires a TQWidget*. For this reason, it is of little value to declare functions to take a QGuardedPtr as a parameter; just use normal pointers. Use a QGuardedPtr when you are storing a pointer over time.
.SH "bool QGuardedPtr::operator!= ( const QGuardedPtr<T> & p ) const"
Inequality operator; implements pointer semantics, the negation of operator==(). Returns TRUE if \fIp\fR and this guarded pointer are not pointing to the same object; otherwise returns FALSE.
.SH "T & QGuardedPtr::operator* () const"
Dereference operator; implements pointer semantics. Just use this operator as you would with a normal C++ pointer.
.SH "T * QGuardedPtr::operator-> () const"
Overloaded arrow operator; implements pointer semantics. Just use this operator as you would with a normal C++ pointer.
.SH "QGuardedPtr<T> & QGuardedPtr::operator= ( const QGuardedPtr<T> & p )"
Assignment operator. This guarded pointer then points to the same object as \fIp\fR points to.
.SH "QGuardedPtr<T> & QGuardedPtr::operator= ( T * p )"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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Assignment operator. This guarded pointer then points to the same object as \fIp\fR points to.
.SH "bool QGuardedPtr::operator== ( const QGuardedPtr<T> & p ) const"
Equality operator; implements traditional pointer semantics. Returns TRUE if both \fIp\fR and this guarded pointer are 0, or if both \fIp\fR and this pointer point to the same object; otherwise returns FALSE.
