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

成员函数重载

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

Ⅱ ++符号的重载

前置++符号重载

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

后置++符号重载

// Coordinate.hppclass 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.cppCoordinate Coordinate::operator++(int) {  Coordinate oldCoor(*this);  m_iX++;  m_iY++;  return oldCoor;}// main.cppint 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.hppclass Coordinate {  friend Coordinate operator+(const Coordinate &coor1, const Coordinate &coor2);  public:    Coordinate(int x, int y);  private:    int m_iX;    int m_iY;};// Coordinate.cppCoordinate 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.cppint 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.hppclass Coordinate {  public:    Coordinate(int x, int y);    Coordinate operator+(const Coordinate &coor);  private:    int m_iX;    int m_iY;};// Coordinate.cppCoordinate 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.cppint 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.cppostream &operator<<(ostream &output, const Coordinate &coor) {  output << coor.m_iX << ", " << coor.m_iY << endl;  return output;}// main.cppint 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.hppclass Coordinate {  public:    Coordinate(int x, int y);      int operator[](int index);  private:    int m_iX;    int m_iY;};// Coordinate.cppint operator[](int index) {  if(index == 0)    return m_iX;  if(index == 1)    return m_iY;}// main.cppint main() {  Coordinate coor(3, 5);    cout << coor[0];  // coor.operator[](0);  cout << coor[1];  // coor.operator[](1);    return 0;}