Xref: utzoo comp.std.c:542 comp.windows.x:6541
Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!ucbvax!bloom-beacon!mcgill-vision!iros1!vedge!lai
From: lai@vedge.UUCP (David Lai)
Newsgroups: comp.std.c,comp.windows.x
Subject: trailing comma inside enum...bug or feature?
Summary: enum { a,b,c, } x;
Message-ID: <2174@vedge.UUCP>
Date: 6 Dec 88 18:42:54 GMT
Organization: Visual Edge Software, St. Laurent, Quebec
Lines: 48

Why does something like:

/* taken straight out of  X11/Intrinsic.h, from Xwindows from MIT */
typedef enum  {
    XtGeometryYes,        /* Request accepted. */
    XtGeometryNo,         /* Request denied. */
    XtGeometryAlmost,     /* Request denied, but willing to take replyBox. */
    XtGeometryDone,       /* Request accepted and done. */
} XtGeometryResult;
	/* note trailing comma after XtGeometryDone */

elicit no complaints from any of the C compilers I use?  I have a couple of
theories:

	1) This is an archaic remnant from bygone days when enums syntax
	   allowed trailing commas
	2) This is a bug in the original C compiler, from which all other C 
	   compilers were ported from.  I suspect this because of the
	   vast number of systems that X has been ported to using the
	   above file.
	3) The books are wrong, the syntax should really read:
		enum_type_def: enum opt_enum_tag { enum_def_list }
			     | enum opt_enum_tag { enum_def_list , }
	4) The C compiler writers were forced to stray from the specification
	   because of files like the above.
	5) Perhaps I'm misinformed, and a trailing comma has some sort of
	   special hidden meaning...

Is this a bug or feature?  Should ANSI compilers allow this?  I only caught
this because I'm designing a C parser directly from the specifications.
I hope somebody in the X consortium sees this (and corrects it for the next
release).

The C standard (and every book on C I've seen, including those from
AT&T) says the syntax of an enum declaration is:

enum_type_def: enum opt_enum_tag { enum_def_list }

enum_def_list: enum_const_def
	     | enum_def_list , enum_const_def

enum_const_def: enum_constant
	      | enum_constant = expression

-- 
	"What is a DJ if he can't scratch?"  - Uncle Jamms Army
The views expressed are those of the author, and not of Visual Edge, nor Usenet.
David Lai (vedge!lai@larry.mcrcim.mcgill.edu || ...watmath!onfcanim!vedge!lai)