运算符重载 笔记1

为什么要使用运算符重载?

C/C++的运算符，支持的数据类型，仅限于基本数据类型。

解决方案：

使用运算符重载

运算符重载的基本用法

方式1：使用成员函数重载运算符

需求：
// 规则：

// 一斤牛肉：2斤猪肉

// 一斤羊肉：3斤猪肉

 

Cow.h

#pragma once

 

class Pork;

class Goat;

 

class Cow

{

public:

    Cow(int weight);

 

    // 参数此时定义为引用类型，更合适，避免拷贝

    Pork operator+(const Cow& cow);  //同类型进行运算，很频繁

 

    Pork operator+(const Goat& goat); //不同类型进行运算，比较少见

private:

    int weight = 0;

};

 

Cow.cpp

#include "Cow.h"

#include "Pork.h"

#include "Goat.h"

 

Cow::Cow(int weight)

{

    this->weight = weight;

}

 

 

// 规则：

// 一斤牛肉：2斤猪肉

// 一斤羊肉：3斤猪肉

Pork Cow::operator+(const Cow &cow)

{

    int tmp = (this->weight + cow.weight) * 2;

    return Pork(tmp);

}

 

Pork Cow::operator+(const Goat& goat)

{

    // 不能直接访问goat.weight

    //int tmp = this->weight * 2 + goat.weight * 3;

    int tmp = this->weight * 2 + goat.getWeight() * 3;

    return Pork(tmp);

}

 

Goat.h

#pragma once

class Goat

{

public:

    Goat(int weight);

    int getWeight(void) const;

private:

    int weight = 0;

};

 

Goat.cpp

#include "Goat.h"

 

Goat::Goat(int weight) {

    this->weight = weight;

}

 

int Goat::getWeight(void) const

{

    return weight;

}

 

Pork.h

#pragma once

#include <iostream>

 

class Pork

{

public:

    Pork(int weight);

    std::string  description(void);

 

private:

    int weight = 0;

};

 

Pork.cpp

#include "Pork.h"

#include <sstream>

 

Pork::Pork(int weight)

{

    this->weight = weight;

}

 

std::string Pork::description(void)

{

    std::stringstream ret;

    ret << weight << "斤猪肉";

    return ret.str();

}

 

main.cpp

#include <iostream>

#include "Pork.h"

#include "Cow.h"

#include "Goat.h"

 

int main(void) {

    Cow c1(100);

    Cow c2(200);

 

    // 调用c1.operator+(c2);

    //相当于：Pork p = c1.operator+(c2);

    Pork p = c1 + c2;

    std::cout << p.description() << std::endl;

 

    Goat g1(100);

    p = c1 + g1;

    std::cout << p.description() << std::endl;

   

    system("pause");

    return 0;

}

 

方式2：使用非成员函数【友元函数】重载运算符

Cow.h

#pragma once

 

class Pork;

class Goat;

 

class Cow

{

public:

    Cow(int weight);

 

    // 有友元函数实现运算符重载

    friend Pork operator+(const Cow& cow1, const Cow& cow2);

    friend Pork operator+(const Cow& cow1, const Goat& goat);

private:

    int weight = 0;

};

 

main.cpp

#include <iostream>

#include "Pork.h"

#include "Cow.h"

#include "Goat.h"

 

Pork operator+(const Cow &cow1, const Cow &cow2)

{

    int tmp = (cow1.weight + cow2.weight) * 2;

    return Pork(tmp);

}

 

Pork operator+(const Cow& cow1, const Goat& goat)

{

    int tmp = cow1.weight * 2 + goat.getWeight() * 3;

    return Pork(tmp);

}

 

int main(void) {

    Cow c1(100);

    Cow c2(200);

    Goat g1(100);

 

    Pork p = c1 + c2;

    std::cout << p.description() << std::endl;

 

    p = c1 + g1;  // 思考：如何实现：p = g1 + c1;

    std::cout << p.description() << std::endl;

 

    system("pause");

    return 0;

}

 

其他文件不变。