Static in header file
本章要讨论的问题是: 定义于header file中的static object和static function。
static function and static object in header file cause duplicate definition
如果添加namespace
是否会避免?
如何查看function是否multiple definition?
compiler对internal linkage的实现方式。
static function in header
https://stackoverflow.com/questions/780730/c-c-static-function-in-header-file-what-does-it-mean
static inline function in header
https://stackoverflow.com/questions/47819719/static-inline-functions-in-a-header-file