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From: lfd@cbnewsm.att.com (Lee Derbenwick)
Newsgroups: comp.lang.c,comp.software-eng
Subject: Re: Source File Organization
Summary: a trick using macros and another include file
Message-ID: <1991Feb27.182525.29758@cbnewsm.att.com>
Date: 27 Feb 91 18:25:25 GMT
References: <1991Feb26.045242.23453@rfengr.com>
Followup-To: comp.lang.c
Organization: AT&T Bell Laboratories
Lines: 42

In article <1991Feb26.045242.23453@rfengr.com>, rfarris@rfengr.com (Rick Farris) writes:
> I have an enumerated type:
> 
> typedef enum { A, B, C, D } CMD;
> 
> and a corresponding array of ascii representations :
> 
> char ltrs[] = { 'A', 'B', 'C', 'D' };
> 
> My problem is: How do I keep the darn things in sync?

This is a bit kludgy, and it doesn't _guarantee_ that they're in
sync (i.e., no protection from typos), but its flexible and
general, and _very_ easy to do.  The key is an include file using
macros that are defined differently in different contexts.

letters.h contains:

  LETTER(A, 'A')
  LETTER(B, 'B')
  LETTER(C, 'C')
  LETTER(D, 'D')
  #undef LETTER

Then, to get your two examples:

  #define LETTER(A,B) A
  typedef enum {
  #include "letters.h"
  } CMD;

  #define LETTER(A,B) B
  char ltrs[] = {
  #include "letters.h"
  };

This trick can also be useful for creating a number of tables
that are really views of a single relation.

 -- Speaking strictly for myself,
 --   Lee Derbenwick, AT&T Bell Laboratories, Warren, NJ
 --   lfd@cbnewsm.ATT.COM  or  <wherever>!att!cbnewsm!lfd