重载运算符

四、重载运算符

​ 概念 : 给原有运算符赋予新功能。

​ 本质 : 函数重载。

​ 关键字 : operator

1.一元运算符重载

​ 符号只与一个操作数进行运算。

Ⅰ -（负号）的重载(取反啊)

• 友元函数重载

  // Coordinate.hpp
  class Coordinate {  friend Coordinate& operator-(Coordinate &coor);public:Coordinate(int x, int y);private:int m_iX;int m_iY;
  };// Coordinate.cpp
  Coordinate& Coordinate::operator-(Coordinate &coor) {coor.m_iX = -coor.m_iX;coor.m_iY = -coor.m_iY;return *this;
  }// main.cpp
  int main() {Coordinate coor(3, 5);-coor;    // operator-(coor);return 0;
  }

  ​

• 成员函数重载

  // Coordinate.hpp
  class Coordinate {public:Coordinate(int x, int y);Coordinate& operator-();    // 有this指针private:int m_iX;int m_iY;
  };// Coordinate.cpp
  Coordinate& Coordinate::operator-() {m_iX = -m_iX;m_iY = -m_iY;return *this;
  }// main.cpp
  int main() {Coordinate coor(3, 5);-coor;    // coor.operator-();return 0;
  }

Ⅱ ++符号的重载

• 前置++符号重载

  // Coordinate.hpp
  class Coordinate {public:Coordinate(int x, int y);Coordinate& operator++();   // 前置++private:int m_iX;int m_iY;
  };// Coordinate.cpp
  Coordinate& Coordinate::operator++() {m_iX++;m_iY++;return *this;
  }// main.cpp
  int main() {Coordinate coor(3, 5);++coor;   // coor.operator++();return 0;
  }

• 后置++符号重载

  // Coordinate.hpp
  class Coordinate {public:Coordinate(int x, int y);Coordinate operator++(int); // 后置++（int用来标识当前的++是后置重载，并不接受任何入参）private:int m_iX;int m_iY;
  };// Coordinate.cpp
  Coordinate Coordinate::operator++(int) {Coordinate oldCoor(*this);m_iX++;m_iY++;return oldCoor;
  }// main.cpp
  int main() {Coordinate coor(3, 5);coor++;   // coor.operator++(0);return 0;
  }

2.二元运算符重载

​ 符号与两个个操作数进行运算。

Ⅰ +（加号）的重载

• 友元函数重载

  // Coordinate.hpp
  class Coordinate {friend Coordinate operator+(const Coordinate &coor1, const Coordinate &coor2);public:Coordinate(int x, int y);private:int m_iX;int m_iY;
  };// Coordinate.cpp
  Coordinate operator+(const Coordinate &coor1, const Coordinate &coor2) {Coordinate tempCoor;tempCoor.m_iX = coor1.m_iX + coor2.m_iX;tempCoor.m_iY = coor1.m_iY + coor2.m_iY;return tempCoor;
  }// main.cpp
  int main() {Coordinate coor1(3, 5);Coordinate coor2(4, 6);Coordinate coor3(0, 0);coor3 = coor1 + coor2;    // coor3 = operator+(coor1, coor2);return 0;
  }

  ​

• 成员函数重载

  // Coordinate.hpp
  class Coordinate {public:Coordinate(int x, int y);Coordinate operator+(const Coordinate &coor);private:int m_iX;int m_iY;
  };// Coordinate.cpp
  Coordinate operator+(const Coordinate &coor) {Coordinate tempCoor;tempCoor.m_iX = this->m_iX + coor.m_iX;tempCoor.m_iY = this->m_iY + coor.m_iY;return tempCoor;
  }// main.cpp
  int main() {Coordinate coor1(3, 5);Coordinate coor2(4, 6);Coordinate coor3(0, 0);coor3 = coor1 + coor2;    // coor3 = coor1.operator+(coor2);return 0;
  }

Ⅱ <<号的重载

• 友元函数重载

  // Coordinate.hpp
  #include <ostream>
  using namespace std;
  class Coordinate {friend ostream &operator<<(ostream &output, const Coordinate &coor);public:Coordinate(int x, int y);private:int m_iX;int m_iY;
  };// Coordinate.cpp
  ostream &operator<<(ostream &output, const Coordinate &coor) {output << coor.m_iX << ", " << coor.m_iY << endl;return output;
  }// main.cpp
  int main() {Coordinate coor(3, 5);cout << coor; // operator<<(cout, coor);return 0;
  }

• 输出运算符可以采用成员函数重载吗？

  不可以。

  因为重载输出运算符的第一个参数必须是ostream &out，而若写成成员函数必须是this指针。

Ⅲ []（索引）的重载

// Coordinate.hpp
class Coordinate {public:Coordinate(int x, int y);  int operator[](int index);private:int m_iX;int m_iY;
};// Coordinate.cpp
int operator[](int index) {if(index == 0)return m_iX;if(index == 1)return m_iY;
}// main.cpp
int main() {Coordinate coor(3, 5);cout << coor[0];  // coor.operator[](0);cout << coor[1];  // coor.operator[](1);return 0;
}

• 索引运算符可以采用友元函数重载吗？

  不可以。

  因为索引运算符的第一个参数必须是this指针。