what is the size of empty class in C++,java?

Question

What is the size of an empty class in C++ and Java? Why is it not zero? sizeof(); returns 1 in the case of C++.

Answer 1

C++ requires that a normal instantiation of it have a size of at least 1 (could be larger, though I don't know of a compiler that does that). It allows, however, an "empty base class optimization", so even though the class has a minimum size of 1, when it's used as a base class it does not have to add anything to the size of the derived class.

I'd guess Java probably does pretty much the same. The reason C++ requires a size of at least 1 is that it requires each object to be unique. Consider, for example, an array of objects with size zero. All the objects would be at the same address, so you'd really only have one object. Allowing it to be zero sounds like a recipe for problems...