c++ - C++ 中虚函数的行为

Question

我有一个问题，下面有两个类:

  class Base{
      public:
          virtual void toString();       // generic implementation
  }

  class Derive : public Base{
      public:
          ( virtual ) void toString();   // specific implementation
  }

问题是:

• 如果我想类Derive 的子类使用Base 类型的指针执行多态性，是否需要括号中的关键字virtual？

• 如果答案是否定的，那么 Derive 类的成员函数 toString 有和没有 virtual 有什么区别？

Answer 1

C++03 §10.3/2:

If a virtual member function vf is declared in a class Base and in a class Derived, derived directly or indirectly from Base, a member function vf with the same name and same parameter list as Base::vf is declared, then Derived::vf is also virtual (whether or not it is so declared) and it overrides Base::vf.