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运算符重载

news 2026/4/19 9:27:06

多态性

多态性从实现角度可以分为两类：静态多态性和动态多态性

静态多态性主要应用于函数重载和运算符重载

动态多态性主要应用于虚函数

运算符重载就是定义函数

运算符重载为成员函数
运算符重载为友元函数

【引例】定义一个复数类，实现复数的加法功能。

方法一：定义一个复数类的ADD()成员函数
错误一:把ADD()当作全局函数来用了，他是类的成员函数，要通过对象打点调用


#include <iostream>using namespace std;class Complex{public:Complex(int,int);Complex();void show();Complex Add(const Complex&,const Complex &); private:int real,image;
};Complex::Complex(){}Complex::Complex(int real,int image):real(real),image(image){}void Complex::show(){//输出该复数//先考虑虚部 if(image>0){if(image==1)cout<<real<<"+"<<"i"<<endl;elsecout<<real<<"+"<<image<<"i"<<endl;}else if(image<0){if(image == -1)cout<<real<<"-"<<"i"<<endl;cout<<real<<image<<"i"<<endl; }elsecout<<real<<endl;} Complex Complex::Add(const Complex & c1,const Complex & c2){Complex res;res.real=c1.real+c2.real;res.image=c1.image+c2.image;return res; }int main(){Complex c1(1,-1),c2(2,3);Complex c3=Add(c1,c2); c1.show();c2.show();c3.show();return 0;
}

改正后


#include <iostream>using namespace std;class Complex{public:Complex(int,int);Complex();void show();Complex Add(const Complex &); private:int real,image;
};Complex::Complex(){}Complex::Complex(int real,int image):real(real),image(image){}void Complex::show(){//输出该复数//先考虑虚部 if(image>0){if(image==1)cout<<real<<"+"<<"i"<<endl;elsecout<<real<<"+"<<image<<"i"<<endl;}else if(image<0){if(image == -1)cout<<real<<"-"<<"i"<<endl;else cout<<real<<image<<"i"<<endl; }elsecout<<real<<endl;} Complex Complex::Add(const Complex & c2){Complex temp;temp.real = this->real+c2.real;temp.image= this->image+c2.image;return temp; }int main(){Complex c1(1,-1),c2(2,3);Complex c3=c1.Add(c2);c1.show();c2.show();c3.show();return 0;
}

方法二：重载为友元函数

重载运算符的规则

返回类型 operator @ (参数表)
{
重载函数体
}

//重载为友元函数#include <iostream>using namespace std;class Complex{public:Complex(int,int);Complex();void show();friend Complex operator+(const Complex&,const Complex &);private:int real,image;
};Complex::Complex(){}Complex::Complex(int real,int image):real(real),image(image){}void Complex::show(){//输出该复数//先考虑虚部 if(image>0){if(image==1)cout<<real<<"+"<<"i"<<endl;elsecout<<real<<"+"<<image<<"i"<<endl;}else if(image<0){if(image == -1)cout<<real<<"-"<<"i"<<endl;else cout<<real<<image<<"i"<<endl; }elsecout<<real<<endl;} Complex operator+(const Complex & c1,const Complex &c2){Complex temp;temp.real=c1.real+c2.real;temp.image=c1.image+c2.image;return temp;} int main(){Complex c1(1,-1),c2(2,3);Complex c3=c1+c2;   //隐式调用c3=operator+(c1,c2);  //显式调用    c1.show();c2.show();c3.show();return 0;
}

临时插入一道题，判断两个复数是否相等

#include <iostream>using namespace std;class Complex{public:Complex(int,int);Complex();void show();friend bool operator == (const Complex & ,const Complex & );private:int real,image;
};Complex::Complex(){}Complex::Complex(int real,int image):real(real),image(image){}void Complex::show(){//输出该复数//先考虑虚部 if(image>0){if(image==1)cout<<real<<"+"<<"i"<<endl;elsecout<<real<<"+"<<image<<"i"<<endl;}else if(image<0){if(image == -1)cout<<real<<"-"<<"i"<<endl;else cout<<real<<image<<"i"<<endl; }elsecout<<real<<endl;} bool operator == (const Complex & c1,const Complex & c2 ){if(c1.real==c2.real&&c1.image==c2.image)return true;return false; }int main(){Complex c1(1,-1),c2(2,3);if(c1 == c2 )cout<<"c1和c2相等"<<endl;elsecout<<"c1和c2不相等"<<endl;	return 0;
}

小练习

方法三：重载为成员函数

#include <iostream>using namespace std;class Complex{public:Complex(int,int);Complex();void show();bool  operator == ( const Complex &  );Complex operator + (const Complex & );private:int real,image;
};Complex::Complex(){}Complex::Complex(int real,int image):real(real),image(image){}void Complex::show(){//输出该复数//先考虑虚部 if(image>0){if(image==1)cout<<real<<"+"<<"i"<<endl;elsecout<<real<<"+"<<image<<"i"<<endl;}else if(image<0){if(image == -1)cout<<real<<"-"<<"i"<<endl;else cout<<real<<image<<"i"<<endl; }elsecout<<real<<endl;} 
bool Complex::operator == ( const Complex & c2 ){// 直接比较：this是当前对象（c1），c2是传入对象return (real == c2.real) && (image == c2.image);
}Complex Complex::operator + (const Complex & c2){Complex temp;temp.real=this->real+c2.real;temp.image=this->image+c2.image;return temp;}int main(){Complex c1(1,-1),c2(1,-1);if(c1.operator ==(c2))cout<<"c1和c2相等"<<endl;elsecout<<"c1和c2不相等"<<endl;	Complex c3 = c1.operator +(c2);c3.show();return 0;
}

几种常用运算符的重载