C++ 输出时间

    time_t timer;
    time(&timer);
    tm* t_tm = localtime(&timer);
    std::string   str = std::to_string(t_tm->tm_year + 1900) + std::to_string(t_tm->tm_mon + 1) +
        std::to_string(t_tm->tm_mday ) + std::to_string(t_tm->tm_hour) + std::to_string(t_tm->tm_min)+std::to_string(t_tm->tm_sec);