Question

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

I’m new to C++, but looked at a few tutorials and read partially Accelerated C++ … but have seen something like

class expr_t : public ast_container {
public:
    virtual double eval() const = 0;
    ...

What does the 1st line mean? Its declaring a class named expr_t? Then whats ast_container part?

Then on line 3: virtual double eval() const = 0 what does it mean?

• Seems like its declaring a virtual function called eval that returns a double, but then whats the const = 0 part?

Answer 1

It means that the parent class/super class/(whatever one calls it) of the expr_t class is the ast_container class. At first glance, it roughly means that everything ast_container can do, expr_t can do it as well, and something more too.