操作符重载
文章目录
- 操作符重载规则
- 单目运算符
- ++（左）
- ++（右）
- 双目操作符重载
- + 运算符
- +=运算符
- << >> 运算符
- = 运算符
- 不建议重载 && 和 ||
- ( ) 的重载
- -> 和 * 的重载
操作符重载规则
- 不能被重载的操作符
| 符号 | 符号举例 |
|---|---|
| . | Peron.name |
| . | Person.name=*(Person.name) |
| :: | 作用域操作符 |
| ？： | 条件操作符 |
- 操作符重载不能改变操作数的个数
- 操作符重载不改变运算顺序（依然先算 * / 后算+ -）
- 操作符重载不改变运算的结合性
- 操作符重载不能有默认参数
- 操作符重载至少要有一个自定义类型
- 操作符重载应当与原来操作符含义相似
- 操作符重载可以是类的成员函数、类的友元函数、还可以是普通函数。
单目运算符
++（左）
说明： ++（左）可以进行连+
class Point
{
//friend Point& operator++(Point& p);
public:Point(int x, int y){m_x = x;m_y = y;}Point& operator++(){++m_x ;++m_y ;return *this;}void Print(){cout << "(" << m_x << " " << m_y << ")" << endl;}
private:
int m_x;int m_y;
};
//Point& operator++(Point& p)
//{
// ++p.m_x;
// ++p.m_y;// return p;
//}int main(void)
{Point A(1, 0);Point B(2, 2);++++A;A.Print();//(3 2)return 0;
}
++（右）
说明：++（右）不能进行连＋
include “stdafx.h”
include
using namespace std;
class Point
{
// friend const Point operator++(Point& p, int);
public:Point(int x, int y){m_x = x;m_y = y;}const Point operator++(int) //因为不能连+的，所以加个const{Point tmp = *this;m_x++;m_y++;return tmp;}void Print(){cout << "(" << m_x << " " << m_y << ")" << endl;}
private:
int m_x;int m_y;
};
//const Point operator++(Point& p, int) //返回的是临时变量，所以不能返回引用//{// Point tmp = p;// p.m_x++;// p.m_y++;// return tmp;//}int main(void){Point A(1, 0);Point B(2, 2);A++;A.Print(); //(2 1)return 0;}
双目操作符重载
重载写法两种：
operator+(L,R) //全局
L.operator+(R) //成员函数
+ 运算符
- 举例：重载+操作符：将两个类相加（对应的成员变量相加）
写法1：全局函数，在类中申明为友元
#include "stdafx.h"#include <iostream>using namespace std;class Point{//friend Point operator+(Point& p1, Point& p2);public:Point(int x, int y){m_x = x;m_y = y;}Point operator+(Point& p2) //定义为成员函数，禁止返回局部变量或者它的引用{Point tmp(this->m_x + p2.m_x, this->m_y + p2.m_y);return tmp;}void Print(){cout << "(" << m_x << " " << m_y << ")" << endl;}private:int m_x;int m_y;};//Point operator+(Point& p1,Point& p2) //重载+操作符，在Point类里面申明为友元,禁止返回局部变量或者它的引用//{// Point tmp(p1.m_x + p2.m_x, p1.m_y + p2.m_y);// return tmp;//}int main(void){Point A(1, 0);Point B(2, 2);Point C = A+B; //全局显式: operator+(A,B) //成员函数显式:A.operator+(B)C.Print();return 0;}
+=运算符
#include "stdafx.h"#include <iostream>using namespace std;class Point{friend Point& operator+=(Point& p1, Point& p2); //申明全局为友元public:Point(int x, int y){m_x = x;m_y = y;}//Point& operator+=(Point& p2) //或者申明成员函数//{// m_x += p2.m_x;// m_y += p2.m_y;// return *this;// }void Print(){cout << "(" << m_x << " " << m_y << ")" << endl;}private:int m_x;int m_y;};Point& operator+=(Point& p1, Point& p2){p1.m_x += p2.m_x;p1.m_y += p2.m_y;return p1;}int main(void){Point A(1, 0);Point B(2, 2);(A+=B)+=B;A.Print();return 0;}
<< >> 运算符
class Point{friend ostream& operator<<(ostream& os, Point& p);public:Point(int x, int y){m_x = x;m_y = y;}// ostream& operator<<(ostream& os) <<操作符禁止写成员函数，否则调用变成: A << cout , 改变本意// {// os << "(" << m_x << " " << m_y << ")";// return os;//}private:int m_x;int m_y;};ostream& operator<<(ostream& os, Point& p){os << "(" << p.m_x << " " << p.m_y << ")" ;return os;}int main(void){Point A(1, 0);Point B(2, 2);cout << A << B << endl;return 0;}
注意： >>也不能写在成员函数内
include “stdafx.h”
include
using namespace std;
class Point
{
friend istream& operator>>(istream& is, Point& p);
public:Point(int x, int y){m_x = x;m_y = y;}void Print(){cout << "(" << m_x << "," << m_y << ")" << endl;}
private:
int m_x;int m_y;
};
istream& operator>>(istream& is, Point& p){cout << "a:";is >> p.m_x;cout << "b:";is >> p.m_y;return is;}int main(void){Point A(1, 0);Point B(2, 2);cin >> A >> B;A.Print();B.Print();return 0;}
= 运算符
#include "stdafx.h"#include <iostream>#include <string.h>using namespace std;class Student{public:Student() //无参构造{m_id = 0;m_name = NULL;}Student(int id, const char name[]) //有参构造{m_id = id;int length = strlen(name);m_name = new char[length + 1];strcpy_s(m_name,length+1,name);}Student(const Student& another) //拷贝构造{m_id = another.m_id;int length = strlen(another.m_name);m_name = new char[length + 1];strcpy_s(m_name, length + 1, another.m_name);}Student& operator=(const Student& another) //=操作符重载,三件事{if(this==&another) return *this;//1. 防止自身赋值m_id = another.m_id;if (m_name != NULL) //2. 判断是否为空，不为空，先释放{delete[]m_name;m_name = NULL;}int length = strlen(another.m_name); //3. 开辟内存m_name = new char[length + 1];strcpy_s(m_name, length + 1, another.m_name);return *this;}void Print(){cout << m_name << ": " << m_id << endl;}~Student(){if (m_name != NULL){delete[] m_name;m_name = NULL;}}private:int m_id;char* m_name;};int main(void){Student A (1, "julian");Student B (2, "mark");Student C (3, "kerr");C =A =B;C.Print(); //mark: 2return 0;}
不建议重载 && 和 ||
- 在已有的运算结构中 &&和 || 都有短路现象：
if(a&&(a=1))如果a是0，那么后面(a=1)应该不执行，结果还是0，但是当你重载&&的时候: object.operator&&(t1), t1作为参数传进去，肯定是执行的，所以不会发生短路现象，但是有时候需要重载又不关心短路现象的时候可以进行重载
( ) 的重载
重载()叫做仿函数,调用形式和函数类似
class Sqr
{
public:Sqr(int a){this->a = a;}//想把s对象 定义成一个 带有一个参数的函数， 求出平方返回//此函数功能就是 对a求平方int operator()(int a){return a*a; //这个a和成员变量无关}
private:
int a;
};
int main(){Sqr A(3); //定义Sqr的对象AA(2); //求2的平方，返回4}
-> 和 * 的重载
参考智能指针章节
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