运算符重载

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;
			else
			cout<<real<<"+"<<image<<"i"<<endl;
		}
		else if(image<0){
			if(image == -1)
			cout<<real<<"-"<<"i"<<endl;
			cout<<real<<image<<"i"<<endl; 
		}
		else
		cout<<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;
			else
			cout<<real<<"+"<<image<<"i"<<endl;
		}
		else if(image<0){
			if(image == -1)
			cout<<real<<"-"<<"i"<<endl;
			else 
			cout<<real<<image<<"i"<<endl; 
		}
		else
		cout<<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;
			else
			cout<<real<<"+"<<image<<"i"<<endl;
		}
		else if(image<0){
			if(image == -1)
			cout<<real<<"-"<<"i"<<endl;
			else 
			cout<<real<<image<<"i"<<endl; 
		}
		else
		cout<<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;
			else
			cout<<real<<"+"<<image<<"i"<<endl;
		}
		else if(image<0){
			if(image == -1)
			cout<<real<<"-"<<"i"<<endl;
			else 
			cout<<real<<image<<"i"<<endl; 
		}
		else
		cout<<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;
	else
	cout<<"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;
			else
			cout<<real<<"+"<<image<<"i"<<endl;
		}
		else if(image<0){
			if(image == -1)
			cout<<real<<"-"<<"i"<<endl;
			else 
			cout<<real<<image<<"i"<<endl; 
		}
		else
		cout<<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;
	else
	cout<<"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