作为类的成员函数，重载运算符只能有一个参数

1 overload a operator of a class, you can only use one para., this pointer is automatically used.

  
  class Rational
  {
    public:
 
  //not correct since this ponit would be used automatically.
  //Rational operator+ (const Rational& lhs, const Rational& rhs);
  
  //correct
  Rational operator+ (const Rational& rhs);
  }

　　

 

2 outside the class two para are allowed

 

Rational operator+(const Rational& lhs, const Rational& rhs))