How can I exclude some C/C++ #ifdef's when generating tags ?
Assume the following source file:

#ifdef __STH__
  some code
  another code

I would like forbid exuberant-ctags to look into "some code" or "another code" depending on whether __STH__ is defined or not.
Is there any option that allows specifying definitions like __STH__.
I think "-I" option is close to do that but unfortunately it does not cover this case (or at least I don't know how to use it properly).

thank you for help