参考：
https://blog.csdn.net/qq_40416052/article/details/82655736?depth_1-utm_source=distribute.pc_relevant.none-task&utm_source=distribute.pc_relevant.none-task
https://www.jb51.net/article/101649.htm
C++ static、const和static const 以及它们的初始化
原文：https://www.cnblogs.com/lh03061238/p/12510207.html
