C++中如何将operator==定义为类的成员函数

#ifndef _DUREE_H
#define _DUREE_H
class Duree{
    public:
    Duree(int heures = 0,int minutes = 0,int secondes = 0);
    bool estEgal(Duree const &b)const;
    bool operator==(Duree const& other);//如果把operator==作为类的成员函数，那么只需要一个参数就够了
    private:
    int m_heures;
    int m_minutes;
    int m_secondes;

};
#endif

#include<iostream>
#include "Duree.h"
using namespace std;
Duree::Duree(int heures,int minutes,int secondes):m_heures(heures),m_minutes(minutes),m_secondes(secondes){
    cout<<m_heures<<" "<<m_minutes<<" "<<m_secondes<<endl;
}
bool Duree::estEgal(Duree const& other)const{
    return (m_heures==other.m_heures && m_minutes == other.m_minutes && m_secondes == other.m_secondes);
}

bool Duree::operator==(Duree const& other){
    return estEgal(other);
}

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

int main(){
    Duree first(10,10,10),second(15,20);
    if(first == second)
        cout<< "Les durees sont identiques"<<endl;
    else
        cout<< "Les durees sont differents"<<endl;

    return 0;
}

/*************************************************************************
	> File Name: copy1.cpp
	> Author: 
	> Mail: 
	> Created Time: 2020年06月17日 星期三 15时36分57秒
 ************************************************************************/

#include<iostream>
using namespace std;

class Example{
    std::string* ptr;
    public:
    Example():ptr(new std::string){}//new std::string返回的值是存储字符串的地址
    Example(const std::string& str):ptr(new std::string(str)){}
    Example(const Example& example):ptr(new std::string(example.content())){};
    ~Example(){delete ptr;}
    const std::string& content()const{return *ptr;}
    Example& operator= (const Example& x){
        cout<<"执行了"<<endl;
        delete ptr;//释放指针指向的字符串占用的内存
        ptr = new string(x.content());
        return *this;
    }
    Example operator+(const Example & rhs){
        return Example(content()+rhs.content());
    }

    void print_information()const{
        cout<< *ptr<<endl;
    }
};

int main(){
    Example bar1("hello");
    bar1.print_information();
    Example bar2("world");
    bar2.print_information();
    Example bar3 = Example(bar1);
    bar3.print_information();
    Example bar4 = bar2;
    bar4.print_information();

    Example foo("Exam");
    Example ba = Example("ple");
    foo = foo + ba;
    cout<<"foo's content:"<<foo.content()<<endl;


    
    return 0;
}