Advantages of an empty class in C++

Question

What could be the possible advantages/uses of having an empty class?

P.S: This question might sound trivial to some of you but it is just for learning purpose and h

Answer 1

As others have said, often an empty class (or struct) is used a placeholder, a differentiator, a token, etc.

For example, a lot of people are unaware that there are "nothrow" versions of operator new. The syntax to invoke nothrow new is:

p = new(std::nothrow) Bar;

and std::nothrow is defined simply as

struct nothrow_t {}; //defined in namespace std