C++运算符重载

运算符重载（操作符重载）：可以为运算符增加一些新的功能。

全局函数、成员函数都支持运算符重载。

#include using namespace std;class Point {friend Point operator+(const Point &, const Point &);int m_x;int m_y;public:Point(int x, int y) : m_x(x), m_y(y) {}void display() {cout << "(" << m_x << ", " << m_y << ")" << endl;}};Point operator+(const Point &p1, const Point &p2) {return Point(p1.m_x + p2.m_x, p1.m_y + p2.m_y);}int main() {Point p1(10, 20);Point p2(20, 30);Point p3 = p1 + p2;p3.display();Point p4 = p1 + p2 + p3;p4.display();getchar();return 0;}

#include using namespace std;class Point {friend ostream &operator<<(ostream &, const Point &);friend istream &operator>>(istream &, Point &);int m_x;int m_y;public:Point(int x, int y) : m_x(x), m_y(y) {}Point(const Point& point) {m_x = point.m_x;m_y = point.m_y;}void display() {cout << "(" << m_x << ", " << m_y << ")" << endl;}const Point operator+(const Point &point) const {return Point(m_x + point.m_x, m_y + point.m_y);}const Point operator-(const Point &point) const {return Point(m_x - point.m_x, m_y - point.m_y);}Point &operator+=(const Point &point) {m_x += point.m_x;m_y += point.m_y;return *this;}bool operator==(const Point &point) const {return (m_x == point.m_x) && (m_y == point.m_y);}bool operator!=(const Point &point) const {return (m_x != point.m_x) || (m_y != point.m_y);}const Point operator-() const {return Point(-m_x, -m_y);}// 前置++Point &operator++() {m_x++;m_y++;return *this;}// 后置++const Point operator++(int) {Point old(m_x, m_y);m_x++;m_y++;return old;}};ostream &operator<<(ostream &cout, const Point &point) {cout << "(" << point.m_x << ", " << point.m_y << ")";return cout;}istream &operator>>(istream &cin, Point &point) {cin >> point.m_x;cin >> point.m_y;return cin;}//class Person {//private://int m_age;//int m_height;//void operator=(const Person &person) {}//public://Person(int age = 0, int height = 0) :m_age(age), m_height(height) {}////void display() {//cout << m_age << ", " << m_height << endl;//}//};int main() {Point p1(10, 20);Point p2(20, 30);Point p3 = p1 + p2;cout << p3 << endl;cin >> p1;cout << p1 << endl;p3 += p1;cout << p3 << endl;getchar();getchar();return 0;}

#include using namespace std;class Person {private:int m_age;int m_height;void operator=(const Person &person) {}public:Person(int age = 0, int height = 0) : m_age(age), m_height(height) {}void display() {cout << m_age << ", " << m_height << endl;}};int main() {Person p1(10, 180);Person p2(11, 175);p1 = p2; // 报错：=重载函数私有化getchar();return 0;}

#include using namespace std;class Person {int m_age;public:Person(int age) : m_age(age) {}Person &operator=(const Person &person) {m_age = person.m_age;return *this;}int getAge() {return m_age;}};class Student : public Person {int m_score;public:Student(int age, int score) : m_score(score), Person(age) {}Student &operator=(const Student &student) {Person::operator=(student);m_score = student.m_score;return *this;}int getScore() {return m_score;}};int main() {Student stu1(18, 90);Student stu2(20, 100);cout << stu2.getAge() << " " << stu2.getScore() << endl;stu2 = stu1;cout << stu2.getAge() << " " << stu2.getScore() << endl;getchar();return 0;}

仿函数：将一个对象当作一个函数一样来使用。

对比普通函数，它作为对象可以保存状态。

#include using namespace std;class Sum {int m_age;public:int operator()(int a, int b) {return a + b;}};int main() {Sum sum;cout << sum(10, 20) << endl; // 等价于sum.operator()(10, 20)getchar();return 0;}

有些运算符不可以被重载，比如
 对象成员访问运算符：.
 域运算符：::
 三目运算符：?:
 sizeof

有些运算符只能重载为成员函数，比如：
赋值运算符 =
下标运算符 []
函数运算符 ()
指针访问成员 ->