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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>QGuardedPtr Class Reference</h1>
<p>The QGuardedPtr class is a template class that provides guarded pointers to QObjects.
<a href="#details">More...</a>
<p><tt>#include <<a href="qguardedptr-h.html">qguardedptr.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="#QGuardedPtr"><b>QGuardedPtr</b></a> ()</li>
<li class=fn><a href="#QGuardedPtr-2"><b>QGuardedPtr</b></a> ( T * p )</li>
<li class=fn><a href="#QGuardedPtr-3"><b>QGuardedPtr</b></a> ( const QGuardedPtr<T> & p )</li>
<li class=fn><a href="#~QGuardedPtr"><b>~QGuardedPtr</b></a> ()</li>
<li class=fn>QGuardedPtr<T> & <a href="#operator-eq"><b>operator=</b></a> ( const QGuardedPtr<T> & p )</li>
<li class=fn>QGuardedPtr<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 QGuardedPtr<T> & p ) const</li>
<li class=fn>bool <a href="#operator!-eq"><b>operator!=</b></a> ( const QGuardedPtr<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 QGuardedPtr class is a template class that provides guarded pointers to QObjects.
<p>
<p> A guarded pointer, <tt>QGuardedPtr<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="qobject.html">QObject</a>.
<p> 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.
<p> Example:
<pre>
QGuardedPtr<QLabel> label = new <a href="qlabel.html">QLabel</a>( 0, "label" );
label->setText( "I like guarded pointers" );
delete (QLabel*) label; // simulate somebody destroying the label
if ( label)
label->show();
else
<a href="qapplication.html#qDebug">qDebug</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 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.
<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 QGuardedPtr<QWidget>, you can pass it to a function that
requires a <a href="qwidget.html">QWidget</a>*. 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.
<p> Note again that class <em>X</em> must inherit <a href="qobject.html">QObject</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="QGuardedPtr"></a>QGuardedPtr::QGuardedPtr ()
</h3>
<p> Constructs a 0 guarded pointer.
<p> <p>See also <a href="#isNull">isNull</a>().
<h3 class=fn><a name="QGuardedPtr-2"></a>QGuardedPtr::QGuardedPtr ( T * p )
</h3>
<p> Constructs a guarded pointer that points to same object as <em>p</em>
points to.
<h3 class=fn><a name="QGuardedPtr-3"></a>QGuardedPtr::QGuardedPtr ( const <a href="qguardedptr.html">QGuardedPtr</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="~QGuardedPtr"></a>QGuardedPtr::~QGuardedPtr ()
</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>QGuardedPtr::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>QGuardedPtr::operator T * () const
</h3>
<p> Cast operator; implements pointer semantics. Because of this
function you can pass a QGuardedPtr<X> to a function where an X*
is required.
<h3 class=fn>bool <a name="operator!-eq"></a>QGuardedPtr::operator!= ( const <a href="qguardedptr.html">QGuardedPtr</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>QGuardedPtr::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>QGuardedPtr::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="qguardedptr.html">QGuardedPtr</a><T> & <a name="operator-eq"></a>QGuardedPtr::operator= ( const <a href="qguardedptr.html">QGuardedPtr</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="qguardedptr.html">QGuardedPtr</a><T> & <a name="operator-eq-2"></a>QGuardedPtr::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>QGuardedPtr::operator== ( const <a href="qguardedptr.html">QGuardedPtr</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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