qobject_cast for Qt3 ?

[sunil.thaha]

Hi Guys,

Just thought like making a qobject_cast for Qt3.
This template functon in Qt4 helps us avoid a lots of typo's So I just thought like making one. this is an intial draft, so please give your suggestions

So here goes the qobject_cast

template < typename T >
inline T* qobject_cast( QObject *object ){
    QObject tmp;
    T instance( &tmp);
    if( object->inherits( instance.className()) ){
        return dynamic_cast< T* >( object );
    }
    return 0;
}

template < typename T >
inline T* qobject_cast( QObject *object ){
    QObject tmp;
    T instance( &tmp);
    if( object->inherits( instance.className()) ){
        return dynamic_cast< T* >( object );
    }
    return 0;
}

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Simple Test App

#include <qpushbutton.h>
#include <qapplication.h>
 
template < typename T >
inline T* qobject_cast( QObject *object ){
    QObject tmp;
    T instance( &tmp);
    if( object->inherits( instance.className()) ){
        return dynamic_cast< T* >( object );
    }
    return 0;
}
 
int main( int argc, char *argv[] ){
 
    QApplication app( argc, argv );
    QObject *obj = new QPushButton(0, "Name");
 
    QPushButton *b = qobject_cast<QPushButton>( obj );
    if( b ){
        qDebug( b->name() );
    }
    return 0;
}

#include <qpushbutton.h>
#include <qapplication.h>

template < typename T >
inline T* qobject_cast( QObject *object ){
    QObject tmp;
    T instance( &tmp);
    if( object->inherits( instance.className()) ){
        return dynamic_cast< T* >( object );
    }
    return 0;
}

int main( int argc, char *argv[] ){

    QApplication app( argc, argv );
    QObject *obj = new QPushButton(0, "Name");

    QPushButton *b = qobject_cast<QPushButton>( obj );
    if( b ){
        qDebug( b->name() );
    }
    return 0;
}

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My inital intend was to create a qobject_cast was
QPushButton *b = qobject_cast< QPushButton * >( object );
Note that the * is missing in the version I have written. Any Ideas ?

[Glitch]

qobject_cast was added to work around problems with dynamic cast over shard objects and the lack of dynamic_cast when RTTI is turned off. I think your code might still exhibit these issues. If you pass the moc inherits test I think you are safe with a static_cast<> which wil work.

--Justin

[camel]

Hi Guys,

Just thought like making a qobject_cast for Qt3.

What is the difference between qtobject_cast in Qt4 and qt_cast in Qt3?

qt_cast is defined in objectdefs.h

[sunil.thaha]

Hey that clue was good I looked in the qobjectdefs.h & then I stumbled upon staticMetaObject() atleast it is there in Qt 3.3.6

So I re wrote the qobject_cast And Guess what ?? you can use qobject_cast< QClassName *>( object );

And for qt_cast : I have no clue ( atleast for now )

So here is the new Code qobject_cast

#include <qmetaobject.h>
 
template < typename T >
inline T qobject_cast( QObject *object ){
    T dummy;
    if( object->inherits( dummy->staticMetaObject()->className()) ){
        return static_cast< T >( object );
    }
    return 0;
}

#include <qmetaobject.h>

template < typename T >
inline T qobject_cast( QObject *object ){
    T dummy;
    if( object->inherits( dummy->staticMetaObject()->className()) ){
        return static_cast< T >( object );
    }
    return 0;
}

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And the Driver still remains the same for most of its part except that now we can use the cast similar to Qt4 's

#include <qmetaobject.h>        // staticMEtaObject used 
 
#include <qpushbutton.h>
#include <qcombobox.h>
#include <qapplication.h>
 
 
template < typename T >
inline T qobject_cast( QObject *object ){
    T dummy;
    if( object->inherits( dummy->staticMetaObject()->className()) ){
        return static_cast< T >( object );
    }
    return 0;
}
 
int main( int argc, char *argv[] ){
 
    QApplication app( argc, argv );
    QObject *obj = new QPushButton(0, "Name");
 
    QComboBox *b = qobject_cast<QComboBox*>( obj );
    if( b ){
        qDebug( b->name() );
    }else {
        qDebug( "Could not typcast ");
    }
    return 0;
}

#include <qmetaobject.h>        // staticMEtaObject used 

#include <qpushbutton.h>
#include <qcombobox.h>
#include <qapplication.h>


template < typename T >
inline T qobject_cast( QObject *object ){
    T dummy;
    if( object->inherits( dummy->staticMetaObject()->className()) ){
        return static_cast< T >( object );
    }
    return 0;
}

int main( int argc, char *argv[] ){

    QApplication app( argc, argv );
    QObject *obj = new QPushButton(0, "Name");

    QComboBox *b = qobject_cast<QComboBox*>( obj );
    if( b ){
        qDebug( b->name() );
    }else {
        qDebug( "Could not typcast ");
    }
    return 0;
}

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