How to delete an already existing layout on a widget?

Question

You must first delete the existing layout manager (returned by layout()) before you can call setLayout() with the new layout.

from http://doc.qt.io/qt-5.9/qwidget.html#setLayout

Which function is used for deleting the previous layout?

Answer 1

You just use

delete layout;

like you would with any other pointer you created using new.