What does the virtual keyword mean when overriding a method?

Question

What does the keyword virtual do when overriding a method? I\'m not using it and everything works fine.

Does every compiler behave the same in this

Answer 1

A virtual method in the base class will cascade through the hierarchy, making every subclass method with the same signature also virtual.

class Base{
public:
  virtual void foo(){}
};

class Derived1 : public Base{
public:
  virtual void foo(){} // fine, but 'virtual' is no needed
};

class Derived2 : public Base{
public:
  void foo(){} // also fine, implicitly 'virtual'
};

I'd recommend writing the virtual though, if for documentation purpose only.