Why do references occupy memory when member of a class?

Question

I have been told that references, when they are data members of classes, they occupy memory since they will be transformed into constant pointers by the compiler. Why is tha

Answer 1

The reference (or pointer) has to be stored in memory somewhere, so why not store it along with the rest of the class?

Even with your example, the parameter a (int &a) is stored in memory (probably on the stack), then a_ref doesn't use any more memory, it's just an alias, but there is memory used by a.