virtual function const vs virtual function non-const

Question

class Base
{
   public:
   virtual void func() const
   {
     cout<<\"This is constant base \"<

        

Answer 1

virtual void func() is actually of a different signature than virtual void func() const. Thus you didn't override your original, read-only base function. You ended up creating a new virtual function instead in Derived.

You can also learn more about this if you ever try to create pointers to member functions (PTMFs), but that's a rare necessity (might be good for study or practice, however).

The override keyword in C++11 is particularly handy to help avoid these kinds of mistakes. The compiler would then tell you that your definition of 'func' in derived does not override anything.