Question

Just wondering why the syntax for virtual functions uses a const before the curly braces, as below:

  virtual void print(int chw, int dus) const;

Incidentally, the code doesnt seem to work without the const, which is interesting.. not sure why?

many thanks!

Answer 1

The const in the function signature signifies a const member function – Anthony Williams gave a great answer on the implications.
Note that there is nothing special about virtual member functions functions in that regard, constness is a concept that applies to all non-static member functions.

As for why its not working without – you can’t call non-const members on a const instance. E.g.:

class C {
public:
  void f1() {}
  void f2() const {}
};

void test() 
{
    const C c;
    c.f1(); // not allowed
    c.f2(); // allowed
}