Empty struct in C vs empty struct in C++

Question

Why is empty struct in C a constraint violation? Why does this rule get changed in C++?

Are there any historical reasons?

Answer 1

since you don't have inheritance in C you don't need them. If you just want to have a distinguishable pointer type you can use pointers to incomplete types.

struct opaque;

struct opaque* stranger = 0;

should work fine.

Answer 2

My guess is this:

In C, there isn't inheritance, templates, and function overloading - three major reasons we use empty structs in C++ - as a base interface, as a template parameter, as a type to help overload resolution.

Can you think of any real use of an empty struct in C?