Why are C++ classes allowed to have zero data members?

Question

question about c++ why minimal number of data members in class definition is zero

i think it should be one , i.e pointer to virtual table defined by compiler

thanks a lot

Answer 1

It is often useful to have a class with no data members for use in inheritance hierarchies.

A base class may only have several typedefs that are used in multiple classes. For example, the std::iterator class template just has the standard types defined so that you don't need to define them in each iterator class.

An interface class typically has no data members, only virtual member functions.

A virtual table has nothing to do with the data members of a class.

Answer 2

Well, actually C++ mandates that all classes must occupy some space (You need to be able to generate a pointer to that class). They only need a pointer to a vtable though, if the class is polymorphic. There's no reason for a vtable at all in a monomorphic class.