C++基础知识 - 重载＜＜和＞＞运算符

重载<<和>>运算符

• 为什么要重载<< 和 >>
  为了更方便的实现复杂对象的输入和输出。
• 在 C++ 中，左移运算符<<可以和 cout 一起用于输出，因此也常被称为“流插入运算符”或者“输出运算符”。
• 实际上，<<本来没有这样的功能，之所以能和 cout 一起使用，是因为被重载了。
• 两种方式实现:
  第一种使用成员函数，不推荐，该方式没有实际意义
  第二种使用友元函数实现

重载<<运算符 方式一：（使用成员函数， 不推荐，该方式没有实际意义）

Boy.h

#pragma once
#include <string>
#include <iostream> 	//包含头文件
using namespace std;

class Boy{
public:
	Boy(const string name = "无名", int age = 0, int salary = 0);

	//输出运算符重载
	ostream& operator<<(ostream& os) const;
private: 
	string name;//姓名
	int age;	//年龄
	int salary;	//薪资
};

Boy.cpp

#include <sstream>
#include "Boy.h"

Boy::Boy(const string name, int age, int salary){
    this->name = name;
    this->age = age;
    this->salary = salary;
}

//返回值是ostream的引用
ostream& Boy::operator<<(ostream& os) const{
    os << "姓名:" << name << "t年龄:" << age << "t薪资:" << salary;
    return os;
}

main.cpp

#include <Windows.h>
#include "Boy.h"
using namespace std;

int main(void) {
	Boy boy1("张三", 18, 10000);
	
	//调用 ostream& operator<<(ostream& os) const;
	boy1 << cout << endl;
	system("pause");
	return 0;
}

重载<<运算符 方式二：使用友元函数

Boy.h

#pragma once
#include <string>
#include <iostream> 
using namespace std;

class Boy{
public:
	Boy(const string name = "无名", int age = 0, int salary = 0);

	//使用友元函数 输出运算符重载
	friend ostream& operator<<(ostream& os, const Boy& boy);
private: 
	string name;//姓名
	int age;	//年龄
	int salary;	//薪资
};

Boy.cpp

#include <sstream>
#include "Boy.h"

Boy::Boy(const string name, int age, int salary){
    this->name = name;
    this->age = age;
    this->salary = salary;
}

main.cpp

#include <Windows.h>
#include "Boy.h"
using namespace std;

//这种方式方便输出 cout<<对象<<endl ;
ostream& operator<<(ostream& os, const Boy& boy) {
	os << "姓名:" << boy.name << "t年龄:" << boy.age << "t薪资:" << boy.salary;
	return os;
}

int main(void) {
	Boy boy1("张三", 18, 10000);
	
	//调用 friend ostream& operator<<(ostream& os, const Boy& boy);
	cout << boy1 << endl;
	system("pause");
	return 0;
}

重载>>运算符: 使用友元函数

Boy.h

#pragma once
#include <string>
#include <iostream> 
using namespace std;

class Boy{
public:
	Boy(const string name = "无名", int age = 0, int salary = 0);
	friend ostream& operator<<(ostream& os, const Boy& boy);

	//使用友元函数 输入运算符重载
	friend istream& operator>>(istream& is, Boy& boy);
private: 
	string name;//姓名
	int age;	//年龄
	int salary;	//薪资
};

Boy.cpp

#include <sstream>
#include "Boy.h"

Boy::Boy(const string name, int age, int salary){
    this->name = name;
    this->age = age;
    this->salary = salary;
}

main.cpp

#include <iostream>
#include <Windows.h>
#include "Boy.h"
using namespace std;

ostream& operator<<(ostream& os, const Boy& boy) {
	os << "姓名:" << boy.name << "t年龄:" << boy.age << "t薪资:" << boy.salary;
	return os;
}

istream& operator>>(istream& is, Boy& boy) {
	cout << "请输入姓名:";
	is >> boy.name;
	cout << "请输入年龄:";
	is >> boy.age;
	cout << "请输入薪资:";
	is >> boy.salary;
	return is;
}

int main(void) {
	Boy boy1("张三", 18, 10000);
	cout << boy1 << endl;

	//调用输入重载运算符 friend istream& operator>>(istream& is, Boy& boy);
	cin >> boy1;	//把张三改为李四#include <iostream>
#include <Windows.h>
#include "Boy.h"

using namespace std;


ostream& operator<<(ostream& os, const Boy& boy) {
	os << "姓名:" << boy.name << "t年龄:" << boy.age << "t薪资:" << boy.salary;
	return os;
}

istream& operator>>(istream& is, Boy& boy) {
	cout << "请输入姓名:";
	is >> boy.name;
	cout << "请输入年龄:";
	is >> boy.age;
	cout << "请输入薪资:";
	is >> boy.salary;
	return is;
}



int main(void) {
	Boy boy1("张三", 18, 10000);
	cout << boy1 << endl;

	//调用输入重载运算符 friend istream& operator>>(istream& is, Boy& boy);
	cin >> boy1;

	cout << boy1 << endl;

	system("pause");
	return 0;
}
	cout << boy1 << endl;	
	system("pause");
	return 0;
}

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