条款50: 提高对C++的认识

class Base {
public:
  virtual void f(int x);
};

class Derived: public Base {
public:
  virtual void f(double *pd);
};

Derived *pd = new Derived;
pd->f(10);                            // 错误!

class Derived: public Base {
public:
  using Base::f;                   // 将Base::f引入到
                                   // Derived的空间范围
  virtual void f(double *pd);
};

Derived *pd = new Derived;
pd->f(10);                         // 正确，调用Base::f