C++: What is the size of an object of an empty class?

Quoting Bjarne Stroustrup's C++ Style and Technique FAQ, the reason the size is non-zero is "To ensure that the addresses of two different objects will be different." And the size can be 1 because alignment doesn't matter here, as there is nothing to actually look at.

The standard states that all most derived objects have sizeof() >= 1:

Unless it is a bit-field (class.bit), a most derived object shall have a non-zero size and shall occupy one or more bytes of storage. Base class sub-objects may have zero size. ISO/IEC FDIS 14882:1998(E) intro.object