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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.lang.c
Subject: Re: Enum vs Define
Message-ID: <21682@sun.uucp>
Date: Sun, 21-Jun-87 17:41:25 EDT
Article-I.D.: sun.21682
Posted: Sun Jun 21 17:41:25 1987
Date-Received: Tue, 23-Jun-87 00:50:05 EDT
References: <196@dbase.UUCP>
Sender: news@sun.uucp
Lines: 43
Keywords: enum, define

> Why use enum instead of #define?  For example, if I've
> got an array of error message strings indexed with ERRMSGA, ERRMSGB
> identifiers, isn't it more robust to explicitly define the values
> (which must correspond to the array) than to let the compiler do it?

Absent a mechanism for declaring arrays with "enum"s as subscripts, the
#defines may be better *in this case*.  However, this is NOT a
typical example of the use of "enum"s.  Most uses of "enum" do not
consider the numerical value used to represent the various values of
the "enum" to be important.  In those cases, the advantages would be:

	1) Better type checking.  The compiler will complain (or,
	   one would hope, warn, even in an ANSI C compiler) about
	   mixing one "enum" type with another.  Such mixing rarely
	   makes sense (the compiler should probably allow the
	   programmer to use casts to indicate that they have
	   determined that mixing does make sense in some particular
	   case).

	2) Better interfaces with debuggers.  If you declare

		enum state { START, STATEA, STATEB, FINAL };

	   a good debugger, when asked to print the value of "state",
	   will print it as "START", "STATEA", "STATEB", or "FINAL".
	   However, if you declare

		int state;

		#define	START	0
		#define	STATEA	1
		#define	STATEB	2
		#define	FINAL	3

	   and ask it to print "state", it will print the numerical
	   value and force you to translate it to something
	   meaningful.

If you could declare arrays indexed by "enum"s, I would use them as
error message indices as well.
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com