概述C++中的 public protected private friend关键字的用法

帮助不大，完全是个骗人的pdf。。有内容完全一样免费的！：https://blog.csdn.net/Awesomewan/article/details/123948929?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522171056135816777224442228%2522%252C%2522scm%2522%253A%252220140713.130102334..%2522%257D&request_id=171056135816777224442228&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~top_positive~default-1-123948929-null-null.142^v99^pc_search_result_base3&utm_term=c%2B%2B%E9%9D%A2%E8%AF%95&spm=1018.2226.3001.4187 2.5节 #毫无价值