How can I draw needle for dial in Qwt

[validator]

I use setNeedle Method but this method want QwtDialNeedle object but QwtDialNeedle is abstract class.How can I do this .

I write this code but I take access violation error.

ui.setupUi(this);
QwtDial *d=new QwtDial(ui.label);
d->setScaleArc(30,330);
d->setScale(100,10,60);
/*d->setOrigin(100);*/
d->setLineWidth(15);
d->setValue(5);	
d->setWrapping(false);
QwtDialNeedle * nd;
d->setNeedle(nd);

ui.setupUi(this);
QwtDial *d=new QwtDial(ui.label);
d->setScaleArc(30,330);
d->setScale(100,10,60);
/*d->setOrigin(100);*/
d->setLineWidth(15);
d->setValue(5);	
d->setWrapping(false);
QwtDialNeedle * nd;
d->setNeedle(nd);

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