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/****************************************************************************
**
** Implementation of TQGuardedPtr class
**
** Created : 990929
**
** Copyright (C) 1992-2008 Trolltech ASA. All rights reserved.
**
** This file is part of the kernel module of the TQt GUI Toolkit.
**
** This file may be used under the terms of the GNU General
** Public License versions 2.0 or 3.0 as published by the Free
** Software Foundation and appearing in the files LICENSE.GPL2
** and LICENSE.GPL3 included in the packaging of this file.
** Alternatively you may (at your option) use any later version
** of the GNU General Public License if such license has been
** publicly approved by Trolltech ASA (or its successors, if any)
** and the KDE Free TQt Foundation.
**
** Please review the following information to ensure GNU General
** Public Licensing retquirements will be met:
** http://trolltech.com/products/qt/licenses/licensing/opensource/.
** If you are unsure which license is appropriate for your use, please
** review the following information:
** http://trolltech.com/products/qt/licenses/licensing/licensingoverview
** or contact the sales department at sales@trolltech.com.
**
** This file may be used under the terms of the Q Public License as
** defined by Trolltech ASA and appearing in the file LICENSE.TQPL
** included in the packaging of this file. Licensees holding valid TQt
** Commercial licenses may use this file in accordance with the TQt
** Commercial License Agreement provided with the Software.
**
** This file is provided "AS IS" with NO WARRANTY OF ANY KIND,
** INCLUDING THE WARRANTIES OF DESIGN, MERCHANTABILITY AND FITNESS FOR
** A PARTICULAR PURPOSE. Trolltech reserves all rights not granted
** herein.
**
**********************************************************************/
#include "qguardedptr.h"
/*!
\class TQGuardedPtr qguardedptr.h
\brief The TQGuardedPtr class is a template class that provides guarded pointers to TQObjects.
\ingroup objectmodel
\mainclass
A guarded pointer, \c{TQGuardedPtr<X>}, behaves like a normal C++
pointer \c{X*}, 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). \c X 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.
Example:
\code
TQGuardedPtr<TQLabel> label = new TQLabel( 0, "label" );
label->setText( "I like guarded pointers" );
delete (TQLabel*) label; // simulate somebody destroying the label
if ( label)
label->show();
else
qDebug("The label has been destroyed");
\endcode
The program will output \c{The label has been destroyed} rather
than dereferencing an invalid address in \c label->show().
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.
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 \c *x or the \c x->member 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 TQGuardedPtr<TQWidget>, you can pass it to a function that
retquires a TQWidget*. 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.
Note again that class \e X must inherit TQObject, or a compilation
or link error will result.
*/
/*!
\fn TQGuardedPtr::TQGuardedPtr()
Constructs a 0 guarded pointer.
\sa isNull()
*/
/*!
\fn TQGuardedPtr::TQGuardedPtr( T* p )
Constructs a guarded pointer that points to same object as \a p
points to.
*/
/*!
\fn TQGuardedPtr::TQGuardedPtr(const TQGuardedPtr<T> &p)
Copy one guarded pointer from another. The constructed guarded
pointer points to the same object that \a p points to (which may
be 0).
*/
/*!
\fn TQGuardedPtr::~TQGuardedPtr()
Destroys the guarded pointer. Just like a normal pointer,
destroying a guarded pointer does \e not destroy the object being
pointed to.
*/
/*!
\fn TQGuardedPtr<T>& TQGuardedPtr::operator=(const TQGuardedPtr<T> &p)
Assignment operator. This guarded pointer then points to the same
object as \a p points to.
*/
/*!
\overload TQGuardedPtr<T> & TQGuardedPtr::operator=(T* p)
Assignment operator. This guarded pointer then points to the same
object as \a p points to.
*/
/*!
\fn bool TQGuardedPtr::operator==( const TQGuardedPtr<T> &p ) const
Equality operator; implements traditional pointer semantics.
Returns TRUE if both \a p and this guarded pointer are 0, or if
both \a p and this pointer point to the same object; otherwise
returns FALSE.
\sa operator!=()
*/
/*!
\fn bool TQGuardedPtr::operator!= ( const TQGuardedPtr<T>& p ) const
Inequality operator; implements pointer semantics, the negation of
operator==(). Returns TRUE if \a p and this guarded pointer are
not pointing to the same object; otherwise returns FALSE.
*/
/*!
\fn bool TQGuardedPtr::isNull() const
Returns \c TRUE if the referenced object has been destroyed or if
there is no referenced object; otherwise returns FALSE.
*/
/*!
\fn T* TQGuardedPtr::operator->() const
Overloaded arrow operator; implements pointer semantics. Just use
this operator as you would with a normal C++ pointer.
*/
/*!
\fn T& TQGuardedPtr::operator*() const
Dereference operator; implements pointer semantics. Just use this
operator as you would with a normal C++ pointer.
*/
/*!
\fn TQGuardedPtr::operator T*() const
Cast operator; implements pointer semantics. Because of this
function you can pass a TQGuardedPtr\<X\> to a function where an X*
is retquired.
*/
/* Internal classes */
TQGuardedPtrPrivate::TQGuardedPtrPrivate( TQObject* o)
: TQObject(0, "_ptrpriv" ), obj( o )
{
if ( obj )
connect( obj, SIGNAL( destroyed() ), this, SLOT( objectDestroyed() ) );
}
TQGuardedPtrPrivate::~TQGuardedPtrPrivate()
{
}
void TQGuardedPtrPrivate::reconnect( TQObject *o )
{
if ( obj == o )
return;
if ( obj )
disconnect( obj, SIGNAL( destroyed() ),
this, SLOT( objectDestroyed() ) );
obj = o;
if ( obj )
connect( obj, SIGNAL( destroyed() ),
this, SLOT( objectDestroyed() ) );
}
void TQGuardedPtrPrivate::objectDestroyed()
{
obj = 0;
}
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