C++裡讓物件可以用cout和cin來做I/O存取

很簡單，利用friend及operator overloading
舉例來說，

class Test {
  public:
    friend istream &operator>> (istream &i, Test &test) {
      return i>>test.data;
    }
    friend ostream &operator<< (ostream &o, const Test &test) {
      return o<<test.data
    }
  private:
    int data;
};

如此一來，就可以使用cout和cin來做類別的I/O了