C++ 运算符重载++

#include <iostream>
using namespace std;

class Good
{
public:
    int member;
    Good(int a): member(a)
    {
        cout << "调用构造" << endl;
        cout << "member =" << member;
    }
    void show()
    {
        cout << member << endl;
    }
    Good operator+(const Good& obj)
    {
        return Good(member - obj.member);
    }
    
    friend ostream& operator<<(ostream& os, Good& obj)
    {
        os << obj.member << "运算符重载" << endl;
        
        return os; //这句话关键，便于重复调用 
    }
    
    Good& operator++()
    {
        member++;
        return *this;
    }
    
    Good operator++(int)
    {
        //下面的注释部分是本函数实现的另一种写法 
        Good old(*this);
        member++;
        return old;
    }
    
//    friend Good operator++(Good& obj, int)
//    {
//        Good old(obj);
//        obj.member++;
//        
//        return old;
//    }
};

int main(int argc, char *argv[])
{
    Good a(10), b(20);
    Good c = a + b;
    cout << c;
    ++c;
    cout << c;
    c++;
    cout << c;
    c.show();
    return 0;
}