C preprocessor macros: check if token was declared

Question

This is for the C preprocessor experts:

How can I declare an enum with a list of some identifiers and later during the switch-statement check if an identifier was included in the list?

Example of what I need:

typedef enum { e1, e2, e3, e4, e5, e6 } e;

e x;
switch (x) {
#if DECLARED_IN_ENUM (e1)
  case e1 : ...
#endif
  /* etc. */
}

I thought of using a Boost sequence and expanding it into a comma separated list in the enum, but how can I check later if the sequence contains a certain token?

EDIT: What I was able to do with Boost is:

#define e1 e1
#define e2 e2
#define e3 e3
#define e4 e4
#define e5 e5
#define e6 e6
#define E (e1)(e2)(e3)(e4)(e5)(e6)

typedef enum { BOOST_PP_SEQ_ENUM(E) } e;

e x;
switch (x) {
#if defined (e1)
  case e1 : ...
#endif
  /* etc. */
}

That is not very beautiful, and I would prefer something like:

#define E (e1)(e2)(e3)(e4)(e5)(e6)

typedef enum { BOOST_PP_SEQ_ENUM(E) } e;

e x;
switch (x) {
#if BOOST_PP_SEQ_CONTAINS (e1,E)
  case e1 : ...
#endif
  /* etc. */
}

but how could BOOST_PP_SEQ_CONTAINS be implemented?

Answer 1

You can't. The C preprocessor doesn't "understand" the C programming language, it just tokenizes it. It doesn't know what "enum" actually means. The compiler handles that.

If you want to test something in the preprocessor, then you'll have to provide preprocessor macros for it to use.

Edit: sorry, missed that you were intending to use Boost.Preprocessor. I don't know whether that can provide the necessary macros, or not, once you've involved something from Boost in the definition of your enum.