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1.重载++和--运算符

  • 自增++和自减--都是一元运算符，它的前置形式和后置形式都可以被重载。请看下面的例子： 
        #include "iostream"
    #include "iomanip"

    using namespace std;

    // 时间类
    class times{
        public:
            times():m_min(0), m_sec(0){};
        public:
            void set_zero(){m_min = 0; m_sec = 0;}
            times run();  // 运行
            times operator++();  // 前置++
            times operator++(int n);  // 后置++,在这个函数中参数n是没有任何意义的，它的存在只是为了区分是前置形式还是后置形式
            friend ostream & operator<< (ostream &out, const times &t);
        private:
            int m_min;
            int m_sec;
    };

    times times::run(){
        ++m_sec;
        if(m_sec == 60){
            m_min++;
            m_sec = 0;
        }
        return *this; 
    }

    times times::operator++(){
        return run();
    }

    times times::operator++(int n){
        times t = *this;
        run();
        return t;  // 对象本身
    }

    ostream & operator<< (ostream &out, const times &t){
        out << setfill('0') << setw(2) << t.m_min << ":" << setw(2) << t.m_sec;
        return out;
    }




    int main(){
        times t1, t2;
        t1 = t2++;

        cout << "t1: "<< t1 <<endl;
        cout << "t2: "<< t2 <<endl;
        t1.set_zero();
        t2.set_zero();
        t1 = ++t2;
        cout << "t1: "<< t1 <<endl;
        cout << "t2: "<< t2 <<endl;

        return 0;
    }