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

class HelloWorld : public Gtk::Window

This means the class HelloWorld is publically derived from class Window defined inside Gtk namespace. Gtk::Window is the fully qualified name of that class.