Static class member

The static member function cannot be declared as const;

Stati data members must be defined outside the body of the class definition. Unlike normal data members, static members are not initialized by a class constructor, but rather should be initialized at the time of definition.

PS: Special integer const static member

In general, static members of a class, like normal data members, can no longer define a class to initialize. Instead, static data members are typically initialized in the definition body.

As long as the initializer is a constant expression, the integer congst static data member can be defined in the class's definition body.

Static class member