What does `class HelloWorld : public Gtk::Window` mean?

Question

I\'m following the Gtk \"Hello World\" tutorial found here, and I\'ve come across a line in a class declaration I\'ve never seen before (I\'ve only been learning to program for

Answer 1

It means that HelloWorld is derived from Gtk::Window, so it inherits its behaviour.

HelloWorld represents a Gtk window, so it is just natural to have it derive from the Gtk's window class. It's constructor will probably add a button to the window (the actual window is created by the parent class constructor, which is invoked automatically when a new instance of HelloWorld is created …) and connect a signal handler (on_button_clicked) to the window.

You can call all of Gtk::Window's methods through an instance of HelloWorld. In turn, HelloWorld can override virtual methods of Gtk::Window to change its behaviour.