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From: oster@dewey.soe.berkeley.edu (David Phillip Oster)
Newsgroups: comp.lang.c
Subject: Re: Enum vs Define
Message-ID: <19913@ucbvax.BERKELEY.EDU>
Date: Thu, 30-Jul-87 18:51:29 EDT
Article-I.D.: ucbvax.19913
Posted: Thu Jul 30 18:51:29 1987
Date-Received: Sat, 1-Aug-87 11:03:35 EDT
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster)
Organization: School of Education, UC-Berkeley
Lines: 48


I missed the beginning of this discussion, so apologies in advance if
this posting just repeats issues that have already been covered.

One hard won bit of knowledge for me is how the difference between
enums and defines can screw you up:

in :
       enum {
                ERRMSGA = 1,
                ERRMSGB = 2
                };
 ERRMSGA is defined to be a subtype of the smallest type that will
hold any of these enums. Since none of these enums are very large,
you'd expect:

sizeof ERRMSGA == sizeof(char)	/* the parens are not necessary on the
			/* left hand side, but they are on the right */

On the other hand, if I had said:

#define ERRMSGA 1
#define ERRMSGB 2

I would expect

sizeof ERRMESGA == sizeof(int)

Ordinarily, this fine distinction is harmless. However, the LightSpeed
C compiler for the macintosh has been augmented with a non-standard
keyword: "pascal". If you declare a function to be of type pascal, the
compiler compiles a different code preamble and postable for the
routine, and things that call the "pascal" routine pass their
arguments to it in a different manner. In particular, the automatic
conversion of char parameters into int parameters gets suppressed. (I
mean, the normal process by which the caller passes a char, the callee
recieves a char, but an int is really being passed on the stack.)

In addition, LightSpeed C acts as if the operating system calls (which
are all of type "pascal") automatically had function prototypes, i.e.
it automatically coerces char to int on operating system calls. Since
operating system calls, and ordinary C calls are handled correctly,
the above oddity will only bite you unless you define a "pascal"
routine of your own.

--- David Phillip Oster            --My Good News: "I'm a perfectionist."
Arpa: oster@dewey.soe.berkeley.edu --My Bad News: "I don't charge by the hour."
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