How get a pointer to the parent widget

[franco.amato]

I think franco's "problem" is that QWidget::parentWidget() returns a pointer to QWidget and he doesn't know how to make it a pointer to QMainWindow. Another one of those C++ problems

Dear Wysota sorry but you're wrong ( I perfectly know what a cast is ). You are used to underestimate me.
tbscope the problem is that QMainWindow doesn't see directly the QWidget.
The QWidgets are created in the centralWidget class that's part of the QMainWindow class.
I use Visual studio.
Thank you.
Franco