C++运算符重载

C++能够重载绝大部分运算符，其中有4个运算符不能被重载，如下表所示：

.	成员选择符
.*	成员对象选择符
：：	域解析操作符
?:	条件操作符
Sizeof()	长度运算符

只能重载为成员函数的运算符，如下表所示：

=	赋值运算符
[]	下标运算符
()	函数运算符
->	间接成员访问
->*	间接取值访问

 

 下面是运算符建议重载：

运算符	建议
所有一元运算符	成员
= [] () -> ->*	必须是成员
+ = -= 、= *= ^= &= != %= > >= < <=	成员
其他二元操作符	非成员

下面写出重载"+"运算符的示例：

#include <iostream>

class OverLoad

{

public:

OverLoad(int x1 = 0, int x2 = 0);

const OverLoad operator +(const OverLoad &other)const;

void print()const;

friend const OverLoad operator+(const OverLoad &object1, const OverLoad &object2);

private:

int operator1;

int operator2;

};

OverLoad::OverLoad(int x1, int x2):

operator1(x1),

operator2(x2)

{

}

const OverLoad OverLoad::operator +(const OverLoad &other)const

{

OverLoad temp;

temp.operator1 = this->operator1 + other.operator1;

temp.operator2 = this->operator2 + other.operator2;

std::cout<<"operator+(const OverLoad &other)"<<std::endl;

return temp;

}

void OverLoad::print()const

{

std::cout<<"operator1:"<<this->operator1<<",  operator2:"<<this->operator2<<std::endl;

}

const OverLoad operator +(const OverLoad &object1, const OverLoad &object2)

{

OverLoad temp;

temp.operator1 = object1.operator1 + object2.operator1;

temp.operator2 = object1.operator2 + object2.operator2;

std::cout<<"operator +(const OverLoad &object1, const OverLoad &object2)"<<std::endl;

return temp;

}

int main()

{

OverLoad object1(10, 15), object2(13, 16);

OverLoad object3 = object1 + object2;

object3.print();

}

上面提供两种方式重载"+"运算符，一种是类的成员函数，另一种是类的友元函数实现，两种实现均能实现重载"+"运算符，区别是他们的作用域不相同。下面是输出结果：

operator +(const OverLoad &object1, const OverLoad &object2)
operator1:23,  operator2:31     

可以看出上面调用的是友元函数重载的"+"运算符，OverLoadobject3=object1+object2;//相当于OverLoad object3 = operator +(object1, object2); 

上面示例是两个对象的类型相同，下面将介绍运算符重载二元操作的操作数的类型不相同。

#include <iostream>

using std::string;

class Mail;

class Sender

{

public:

Sender(string address);

Sender &operator <<( Mail &mail);

private:

string m_address;

};

Sender::Sender(string address)

:m_address(address)

{

}

class Mail

{

public:

Mail(string title, string content, string time);

friend Sender &Sender::operator <<( Mail &mail);

private:

string m_title;

string m_content;

string m_time;

};

Mail::Mail(string title, string content, string time)

:m_title(title),

m_content(content),

m_time(time)

{

}

Sender & Sender::operator <<( Mail &mail)

{

std::cout<<m_address<<std::endl;

std::cout<<mail.m_title<<std::endl;

std::cout<<mail.m_content<<std::endl;

std::cout<<mail.m_time<<std::endl;

return *this;

}

int main()

{

Sender sender("zhang1994J@163.com");

Mail mail1("吃饭","中午去吃饭","2016-06-13 11-00"), mail2("午休", "中午午休", "2016-06-13 12-45");

sender<<mail1<<mail2;

}
输出如下：

zhang1994J@163.com

吃饭

中午去吃饭

2016-06-13 11-00

zhang1994J@163.com

午休

中午午休

2016-06-13 12-45