operator=处理自我赋值

class Widget {
public:
  Widget(int x=0): val(new int(x)) {}
  ~Widget() { delete val; }
  Widget(const Widget &rhs): val(new int(*rhs.val)) {}
  //operator =
  Widget& operator=(const Widget &rhs);

  void print() const { cout << *val << endl; }
private:
  int *val;
};

错误版本：

/** wrong version
 * not-safe when self-assignment occurs.
 */
Widget& Widget::operator=(const Widget &rhs) {
  delete val;
  val = new int(*rhs.val);
  return *this;
}

改进版本1：

Widget& Widget::operator=(const Widget &rhs) {
  if(this == &rhs) return;

  delete val;
  val = new int(*rhs.val);
  return *this;
}

改进版本2：

Widget& Widget::operator=(const Widget &rhs) {
  int *pOld = val;
  val = new int(*rhs.val);
  delete pOld;
  return *this;
}

改进版本3:

Widget& Widget::operator=(const Widget &rhs) {
  Widget temp(rhs);
  swap(temp);
  return *this;
}

改进版本4:

Widget& Widget::operator=(Widget rhs) { //yes, copy by value
  swap(rhs);
  return *this;
}

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operator=处理自我赋值

原文：http://blog.csdn.net/shoulinjun/article/details/36212035