Question

A signal is a special member function declared in a class declaration. It can have a
parameter list but no function body. It cannot be called but can be emitted by an
instance of the class.

A slot is a special void member function that can be connected to a signal. Then
when the signal is emitted, the slot is called. A slot can also be called as a normal
member function.

can signal and slots work across objects of different classes?

Answer 1

They can indeed work across objects of different classes, that’s the whole point.

Qt uses signals and slots quite extensively, look at their description:

Qt Signals and Slots