说明：  文档为孙鑫老师的关于vc的学习笔记,让你更好的学习VC,为了方便大家的学习,特意上传来,让大家学习之用
(Documentation for the Sun Xin teachers on vc the study notes, you better learn VC, in order to facilitate everyone' s learning, specifically to upload, so use them to learn)