.BI "\fBQGuardedPtr\fR ( const QGuardedPtr<T> & p )"
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.BI "\fB~QGuardedPtr\fR ()"
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.BI "QGuardedPtr<T> & \fBoperator=\fR ( const QGuardedPtr<T> & p )"
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.BI "QGuardedPtr<T> & \fBoperator=\fR ( T * p )"
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.BI "bool \fBoperator==\fR ( const QGuardedPtr<T> & p ) const"
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.BI "bool \fBoperator!=\fR ( const QGuardedPtr<T> & p ) const"
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.BI "bool \fBisNull\fR () const"
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.BI "T * \fBoperator->\fR () const"
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.BI "T & \fBoperator*\fR () const"
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.BI "\fBoperator T *\fR () const"
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.SH DESCRIPTION
The QGuardedPtr class is a template class that provides guarded pointers to QObjects.
.PP
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 QObject.
.PP
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.
.PP
Example:
.PP
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QGuardedPtr<QLabel> label = new QLabel( 0, "label" );
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label->setText( "I like guarded pointers" );
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delete (QLabel*) label; // simulate somebody destroying the label
The program will output \fCThe label has been destroyed\fR rather than dereferencing an invalid address in \fClabel->show()\fR.
.PP
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.
.PP
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<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 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.
.PP
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.
