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C++基础知识之运算符重载

骆驼胡杨 人气:0

运算符重载

-C/C++的运算符,支持的数据类型,仅限于基本数据类型。

一个圆 +一个圆 = ? (想要变成一个更大的圆)
一头牛 – 一只羊 = ? (想要变成4只羊,原始的以物易物:1头牛价值5只羊)

使用运算符重载

方式一, 使用成员函数重载运算符 需求:把牛肉换猪肉, 羊肉换猪肉

规则:

一斤牛肉:2斤猪肉

一斤羊肉:3斤猪肉

实现:

牛 + 牛 = ?猪肉

牛 + 羊 = ?猪肉

 Cow类

> Cow.h
#pragma once
class Pork;
class Sheep;	
class Cow{	//牛类
public:
	Cow(int weight = 0);
	//使用运算符重载, 实现 牛肉 + 牛肉 = 猪肉 
	Pork operator+(const Cow& cow);
	//使用运算符重载, 实现 牛肉 + 羊肉 = 猪肉 
	Pork operator+(const Sheep& sheep);
private:
	int weight;	//重量
};
_________________________________________________________________________________________________________________________________
> Cow.cpp
#include "Cow.h"
#include "Pork.h"
#include "Sheep.h"
Cow::Cow(int weight){
	this->weight = weight;
}
//一斤牛肉换两斤猪肉
Pork Cow::operator+(const Cow& cow){	
	return Pork((this->weight + cow.weight) * 2);
}
//一斤牛肉换两斤猪肉, 一斤羊肉换三斤猪肉
Pork Cow::operator+(const Sheep& sheep){
	int tmp = (this->weight * 2) + (sheep.getWeight() * 3);
	return Pork(tmp);
}

 Sheep类

> Sheep.h
#pragma once
//羊类
class Sheep{
public:
	Sheep(int weight = 0);
	int getWeight() const;
private:
	int weight;	//重量
};
_________________________________________________________________________________________________________________________________
> Sheep.cpp
#include "Sheep.h"
Sheep::Sheep(int weight){
	this->weight = weight;
}
int Sheep::getWeight() const{
	return weight;
}

Pork类

> Pork.h
#pragma once
#include <string>
using namespace std;
class Pork{	//猪肉类
public:
	Pork(int weight = 0);
	string description() const;
private:
	int weight;
};
_________________________________________________________________________________________________________________________________
> Pork.cpp
#include <sstream>
#include "Pork.h"
Pork::Pork(int weight){
	this->weight = weight;
}
string Pork::description() const{
	stringstream ret;
	ret << this->weight << "斤";
	return ret.str();
}

main.cpp

#include <iostream>
#include <Windows.h>
#include "Cow.h"
#include "Pork.h"
#include "Sheep.h"
using namespace std;
int main(void) {
	Pork p1;
	Cow c1(100);
	Cow c2(200);
	Sheep s1(100);
	//调用运算符重载 Pork operator+(const Cow& cow);
	p1 = c1 + c2;
	cout << "牛 + 牛 = 猪肉:" << p1.description() << endl;
	//调用运算符重载 Pork operator+(const Sheep& c1);
	p1 = c1 + s1;
	cout << "牛 + 羊 = 猪肉:" << p1.description() << endl;
	//羊+牛会报错, 因为没有定义对应的羊+牛运算符重载
	//p1 = s1 + c1;
	system("pause");
	return 0;
}

方式二, 使用非成员函数【友元函数】重载运算符

实现:

牛 + 牛 = ?猪肉

牛 + 羊 = ?猪肉

 Cow类

> Cow.h
#pragma once
class Pork;
class Sheep;	
class Cow{	//牛类
public:
	Cow(int weight = 0);
	//使用友元运算符重载, 实现 牛肉 + 牛肉 = 猪肉 
	friend Pork operator+(const Cow& c1, const Cow& c2);
	//使用友元运算符重载, 实现 牛肉 + 羊肉 = 猪肉 
	friend Pork operator+(const Cow& c1, const Sheep& s1);
private:
	int weight;	//重量
};
_________________________________________________________________________________________________________________________________
> Cow.cpp
#include "Cow.h"
Cow::Cow(int weight){
	this->weight = weight;
}

 Sheep类

> Sheep.h
#pragma once
//羊类
class Sheep{
public:
	Sheep(int weight = 0);
	int getWeight() const;
private:
	int weight;	//重量
};
_________________________________________________________________________________________________________________________________
> Sheep.cpp
#include "Sheep.h"
Sheep::Sheep(int weight){
	this->weight = weight;
}
int Sheep::getWeight() const{
	return weight;
}

Pork类

> Pork.h
#pragma once
#include <string>
using namespace std;
class Pork{	//猪肉类
public:
	Pork(int weight = 0);
	string description() const;
private:
	int weight;
};
_________________________________________________________________________________________________________________________________
> Pork.cpp
#include <sstream>
#include "Pork.h"
Pork::Pork(int weight){
	this->weight = weight;
}
string Pork::description() const{
	stringstream ret;
	ret << this->weight << "斤";
	return ret.str();
}

main.cpp

#include <iostream>
#include <Windows.h>
#include "Cow.h"
#include "Pork.h"
#include "Sheep.h"
using namespace std;
//要想访问类的私有数据成员, 就把这个函数定义为友元
Pork operator+(const Cow& c1, const Cow& c2) {
	return ((c1.weight + c2.weight) * 2);
}
//要想访问类的私有数据成员, 就把这个函数定义为友元
Pork operator+(const Cow& c1, const Sheep& s1) {
	return((c1.weight * 2) + (s1.getWeight() * 3));
}
int main(void) {
	Pork p1;		
	Cow c1(100);	//100斤的牛
	Cow c2(200);	//200斤的牛
	Sheep s1(100);	//100斤的羊
	//调用 friend Pork operator+(const Cow& c1, const Cow& c2);
	p1 = c1 + c2;
	cout << "使用友元 牛 + 牛 = 猪肉:" << p1.description() << endl;
	//调用 friend Pork operator+(const Cow& c1, const Sheep& s1);
	p1 = c1 + s1;
	cout << "使用友元 牛 + 羊 = 猪肉:" << p1.description() << endl;
	system("pause");
	return 0;
}

两种方式的区别

区别:

使用成员函数来实现运算符重载时,少写一个参数,因为第一个参数就是this指针。

两种方式的选择:

方便实现a+b和b+a相同的效果,成员函数方式无法实现。

例如: 100 + cow; 只能通过友元函数来实现

cow +100; 友元函数和成员函数都可以实现

(1)= () [ ] -> 不能重载为类的友元函数!!!(否则可能和C++的其他规则矛盾),只能使用成员函数形式进行重载。

(2)如果运算符的第一个操作数要求使用隐式类型转换,则必须为友元函数(成员函数方式的第一个参数是this指针)

注意:

同一个运算符重载, 不能同时使用两种方式来重载,会导致编译器不知道选择哪一个(二义性)

总结

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