QDateTime相减

    QString begin = "2021-07-02 12:00:00";

    QDateTime begin_time = QDateTime::fromString(begin, "yyyy-MM-dd hh:mm:ss");

    QDateTime end = QDateTime::currentDateTime();

    int start_time = begin_time.toTime_t();

    int end_time = end.toTime_t();

    int t_Ret = end_time - start_time;