参考文献: What is Static Member Function in C++?
1. static member variable 不需要依赖类的实例而存在
2. static member variable 可以作为类的实例的计数器(见链接例子)
3. static member variable 要满足全局而不只是翻译单元的一处定义原则,所以,一般定义在cpp,或者声明为inline

参考文献: What is Static Member Function in C++?
1. static member variable 不需要依赖类的实例而存在
2. static member variable 可以作为类的实例的计数器(见链接例子)
3. static member variable 要满足全局而不只是翻译单元的一处定义原则,所以,一般定义在cpp,或者声明为inline