I think the more important observation is that this needn't be a member at all.  There's no reason to expose it outside the cpp and in this case it could be #defined.

My suggestion on g_ is base on the usage implications of the member being static when the class is instantiated. When I see m_ I think "Hey modifying this guy only affects THIS instance of the class."  This isn't the case for a static member and could lead to misuse.