hou_j Some practice of constructor etc. For more information: https://www.bilibili.com/video/av19038490 https://www.cnblogs.com/LearningTheLoad/tag/C%2B%2B%E9%9D%A2%E5%90%91%E5%AF%B9%E8%B1%A1%E9%AB%98%E7%BA%A7%E7%BC%96%E7%A8%8B/