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< td align = "right" valign = "center" > < img src = "logo32.png" align = "right" width = "64" height = "32" border = "0" > < / td > < / tr > < / table > < h1 align = center > TQGuardedPtr Class Reference< / h1 >
< p > The TQGuardedPtr class is a template class that provides guarded pointers to TQObjects.
< a href = "#details" > More...< / a >
< p > < tt > #include < < a href = "qguardedptr-h.html" > ntqguardedptr.h< / a > > < / tt >
< p > < a href = "qguardedptr-members.html" > List of all member functions.< / a >
< h2 > Public Members< / h2 >
< ul >
< li class = fn > < a href = "#TQGuardedPtr" > < b > TQGuardedPtr< / b > < / a > ()< / li >
< li class = fn > < a href = "#TQGuardedPtr-2" > < b > TQGuardedPtr< / b > < / a > ( T * p )< / li >
< li class = fn > < a href = "#TQGuardedPtr-3" > < b > TQGuardedPtr< / b > < / a > ( const TQGuardedPtr< T> & p )< / li >
< li class = fn > < a href = "#~TQGuardedPtr" > < b > ~TQGuardedPtr< / b > < / a > ()< / li >
< li class = fn > TQGuardedPtr< T> & < a href = "#operator-eq" > < b > operator=< / b > < / a > ( const TQGuardedPtr< T> & p )< / li >
< li class = fn > TQGuardedPtr< T> & < a href = "#operator-eq-2" > < b > operator=< / b > < / a > ( T * p )< / li >
< li class = fn > bool < a href = "#operator-eq-eq" > < b > operator==< / b > < / a > ( const TQGuardedPtr< T> & p ) const< / li >
< li class = fn > bool < a href = "#operator!-eq" > < b > operator!=< / b > < / a > ( const TQGuardedPtr< T> & p ) const< / li >
< li class = fn > bool < a href = "#isNull" > < b > isNull< / b > < / a > () const< / li >
< li class = fn > T * < a href = "#operator--gt" > < b > operator-> < / b > < / a > () const< / li >
< li class = fn > T & < a href = "#operator*" > < b > operator*< / b > < / a > () const< / li >
< li class = fn > < a href = "#operator-T-*" > < b > operator T *< / b > < / a > () const< / li >
< / ul >
< hr > < a name = "details" > < / a > < h2 > Detailed Description< / h2 >
The TQGuardedPtr class is a template class that provides guarded pointers to TQObjects.
< p >
< p > A guarded pointer, < tt > TQGuardedPtr< X> < / tt > , behaves like a normal C++
pointer < tt > X*< / tt > , 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). < tt > X< / tt > must be a
subclass of < a href = "ntqobject.html" > TQObject< / a > .
< p > 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.
< p > Example:
< pre >
TQGuardedPtr< TQLabel> label = new < a href = "ntqlabel.html" > TQLabel< / a > ( 0, "label" );
label-> setText( "I like guarded pointers" );
delete (TQLabel*) label; // simulate somebody destroying the label
if ( label)
label-> show();
else
< a href = "ntqapplication.html#qDebug" > tqDebug< / a > ("The label has been destroyed");
< / pre >
< p > The program will output < tt > The label has been destroyed< / tt > rather
than dereferencing an invalid address in < tt > label-> show()< / tt > .
< p > The functions and operators available with a TQGuardedPtr 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.
< p > 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 < a href = "#operator-eq-eq" > operator==< / a > () and
< a href = "#operator!-eq" > operator!=< / a > (), or test for 0 with < a href = "#isNull" > isNull< / a > (). And you can dereference
them using either the < tt > *x< / tt > or the < tt > x-> member< / tt > notation.
< p > 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 TQGuardedPtr< TQWidget > , you can pass it to a function that
requires a < a href = "ntqwidget.html" > TQWidget< / a > *. For this reason, it is of little value to
declare functions to take a TQGuardedPtr as a parameter; just use
normal pointers. Use a TQGuardedPtr when you are storing a pointer
over time.
< p > Note again that class < em > X< / em > must inherit < a href = "ntqobject.html" > TQObject< / a > , or a compilation
or link error will result.
< p > See also < a href = "objectmodel.html" > Object Model< / a > .
< hr > < h2 > Member Function Documentation< / h2 >
< h3 class = fn > < a name = "TQGuardedPtr" > < / a > TQGuardedPtr::TQGuardedPtr ()
< / h3 >
< p > Constructs a 0 guarded pointer.
< p > < p > See also < a href = "#isNull" > isNull< / a > ().
< h3 class = fn > < a name = "TQGuardedPtr-2" > < / a > TQGuardedPtr::TQGuardedPtr ( T * p )
< / h3 >
< p > Constructs a guarded pointer that points to same object as < em > p< / em >
points to.
< h3 class = fn > < a name = "TQGuardedPtr-3" > < / a > TQGuardedPtr::TQGuardedPtr ( const < a href = "ntqguardedptr.html" > TQGuardedPtr< / a > < T> & p )
< / h3 >
< p > Copy one guarded pointer from another. The constructed guarded
pointer points to the same object that < em > p< / em > points to (which may
be 0).
< h3 class = fn > < a name = "~TQGuardedPtr" > < / a > TQGuardedPtr::~TQGuardedPtr ()
< / h3 >
< p > Destroys the guarded pointer. Just like a normal pointer,
destroying a guarded pointer does < em > not< / em > destroy the object being
pointed to.
< h3 class = fn > bool < a name = "isNull" > < / a > TQGuardedPtr::isNull () const
< / h3 >
< p > Returns < tt > TRUE< / tt > if the referenced object has been destroyed or if
there is no referenced object; otherwise returns FALSE.
< h3 class = fn > < a name = "operator-T-*" > < / a > TQGuardedPtr::operator T * () const
< / h3 >
< p > Cast operator; implements pointer semantics. Because of this
function you can pass a TQGuardedPtr< X> to a function where an X*
is required.
< h3 class = fn > bool < a name = "operator!-eq" > < / a > TQGuardedPtr::operator!= ( const < a href = "ntqguardedptr.html" > TQGuardedPtr< / a > < T> & p ) const
< / h3 >
< p > Inequality operator; implements pointer semantics, the negation of
< a href = "#operator-eq-eq" > operator==< / a > (). Returns TRUE if < em > p< / em > and this guarded pointer are
not pointing to the same object; otherwise returns FALSE.
< h3 class = fn > T & < a name = "operator*" > < / a > TQGuardedPtr::operator* () const
< / h3 >
< p > Dereference operator; implements pointer semantics. Just use this
operator as you would with a normal C++ pointer.
< h3 class = fn > T * < a name = "operator--gt" > < / a > TQGuardedPtr::operator-> () const
< / h3 >
< p > Overloaded arrow operator; implements pointer semantics. Just use
this operator as you would with a normal C++ pointer.
< h3 class = fn > < a href = "ntqguardedptr.html" > TQGuardedPtr< / a > < T> & < a name = "operator-eq" > < / a > TQGuardedPtr::operator= ( const < a href = "ntqguardedptr.html" > TQGuardedPtr< / a > < T> & p )
< / h3 >
< p > Assignment operator. This guarded pointer then points to the same
object as < em > p< / em > points to.
< h3 class = fn > < a href = "ntqguardedptr.html" > TQGuardedPtr< / a > < T> & < a name = "operator-eq-2" > < / a > TQGuardedPtr::operator= ( T * p )
< / h3 >
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
< p > Assignment operator. This guarded pointer then points to the same
object as < em > p< / em > points to.
< h3 class = fn > bool < a name = "operator-eq-eq" > < / a > TQGuardedPtr::operator== ( const < a href = "ntqguardedptr.html" > TQGuardedPtr< / a > < T> & p ) const
< / h3 >
< p > Equality operator; implements traditional pointer semantics.
Returns TRUE if both < em > p< / em > and this guarded pointer are 0, or if
both < em > p< / em > and this pointer point to the same object; otherwise
returns FALSE.
< p > < p > See also < a href = "#operator!-eq" > operator!=< / a > ().
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