Question

I am a beginner of C++, I am studying virtual functions these days.
There are some questions confuse me a lot.

for example:

class A {
  public:
  virtual void f() {
      //do something; 
  }
}

class B: public A {
   public:
   virtual void f() {
//do something;
}
}

1. class A contains a virtual function f(), and class B inherits it. Inside class B, the function f() is also declared as virtual, so does this mean f() in class B overloads f() in class A? Does it allow classes which inherit B to overload f()? Or does B define a new virtual function which is different from f() in class A?

2. Virtual functions provide a way of overloading methods. If B inherits A and does not declare the f() as virtual, then can a class C which inherits B overload the f() and achieve polymorphism?

Answer 1

inside class B, the function f() also be declared as virtual, so does this mean f() in class B overload f() in class A

No, it doesn’t overload. It overrides. Also the keyword virtual is optional in class B. B::f() will always be a virtual function, whether you write virtual or not.

The term overload is used when you define a function with same name but different parameter(s). In your case, the signature of the function f is exactly same in both classes, that means it isn’t overloading; the derived class basically overrides the base class definition of f().