4.0 C++远征：重载运算符

重载运算符

[TOC]

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 
  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。