菜单类界面，其中涉及多窗口及数据库，进度条，时间显示等内容-Menu type interface, which involves multi-window and the database, progress bar, time display, etc.

qt开发的图书管理系统，对数据库操作和多窗口设计具有一定的指导意义！-Library management system QT, which has a certain guiding significance to the database operation and multi window design!