help dynamic_cast

[giorgik]

I have a problem to make the

dynamic_cast<Ostacolo *>(ostacolo)

dynamic_cast<Ostacolo *>(ostacolo)

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see the following code snippet:

QList<QGraphicsItem *> collisioniOstacolo = scene()->collidingItems(this);
QList<QGraphicsItem *>::Iterator iter;
for(iter = collisioniOstacolo.begin(); iter != collisioniOstacolo.end(); ++iter)
{
    QGraphicsItem *ostacolo = *iter;
    if((*iter)->collidesWithItem(this))
    {
         Ostacolo *pOstacolo = dynamic_cast<Ostacolo *>(ostacolo);
         qDebug() << "Toccato un " << pOstacolo->objectName();
    }
}

QList<QGraphicsItem *> collisioniOstacolo = scene()->collidingItems(this);
QList<QGraphicsItem *>::Iterator iter;
for(iter = collisioniOstacolo.begin(); iter != collisioniOstacolo.end(); ++iter)
{
    QGraphicsItem *ostacolo = *iter;
    if((*iter)->collidesWithItem(this))
    {
         Ostacolo *pOstacolo = dynamic_cast<Ostacolo *>(ostacolo);
         qDebug() << "Toccato un " << pOstacolo->objectName();
    }
}

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I get this error when compiling:

C:\Qt\4.8.3\src\corelib\global\qglobal.h:2505: error: 'dynamic_cast_will_always_fail_because_rtti_is_disabled' is not a member of 'Ostacolo*'

C:\Qt\4.8.3\src\corelib\global\qglobal.h:2505: error: 'dynamic_cast_will_always_fail_because_rtti_is_disabled' is not a member of 'Ostacolo*'

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What did I do wrong?