Question

I heard that the widgets should be allocated on the heap (using new), and then there are no needs to delete them (it is done automatically).

1. Can someone explain why?
2. What happens if a widget is not allocated that way, but on a stack?

I am not sure if it matters, but all widgets I am creating have a parent.

This says :

If parent is 0, the new widget becomes
a window. If parent is another widget,
this widget becomes a child window
inside parent. The new widget is
deleted when its parent is deleted.

Answer 1

There’s no magic involved. Simply put, a QObject automatically deletes its children in its destructor. So, as long as your widget has a parent and that you destroy that parent, you don’t have to worry about the children. So if you wondered what was that QObject * parent parameter, well, that’s what it’s there for.

Also, from the doc:

All child objects are deleted. If any of these objects are on the stack or global, sooner or later your program will crash.

So, avoid giving parents to objects that are stack-allocated.