Out of class definition of static const integral or enum members Static const整型(或枚举)成员的类外定义
Assigning additional values new versions of enums , or changing the values of the enum members in a new version , can cause problems for dependant source code 如果给新版本的枚举赋其他值,或者更改新版本中枚举成员的值,可能引起相关源代码的问题。