Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!princeton!allegra!alice!shopiro
From: shopiro@alice.UUCP
Newsgroups: comp.lang.c++
Subject: Re: Constant expressions
Message-ID: <6426@alice.uUCp>
Date: Fri, 5-Dec-86 09:44:13 EST
Article-I.D.: alice.6426
Posted: Fri Dec  5 09:44:13 1986
Date-Received: Fri, 5-Dec-86 21:18:21 EST
References: <1252@cit-vax.Caltech.Edu>
Organization: AT&T Bell Laboratories, Murray Hill NJ
Lines: 30
Summary: SUN's illegal casts can be eliminated with no effect.

In article <1252@cit-vax.Caltech.Edu>, jon@oddhack.Caltech.Edu (Jon Leech) writes:
> 
> 	I recently found that C++ (1.1) does not allow integral casts in
> constant expressions in some cases; for example,
> 
> 	typedef enum { one = (unsigned)1 } ENUM;
> 
> Unfortunately, this makes it impossible to include some of the graphics header
> files on Suns which use this form (it also happens to disagree with 
> the ANSI C draft, sadly).  Has anyone got a fix for this problem?

This code (or any code that uses casts in constant expressions) is not
legal C according to Ritchie* or the ANSI draft.  Apparently some C
compilers will accept it;  I believe there are others that won't.
C++ has already abandoned complete upward compatability with legal
C -- it's unreasonable to expect it to be compatible with illegal C.

I grant that it is clear what such casts would mean if they were
legal, and that there are examples where they might allow you to
write code that couldn't be written as directly otherwise.  I am
confident that if this extension were approved by the ANSI committee
it would also appear in C++.

However, in all the SUN header examples I have looked at, the cast is
pure noise and can be eliminated with no effect whatsoever.  That is
what I suggest you do.  (When you're done, I'm sure there will be many
people who would like a copy).

* Dennnis Ritchie, The C Programming Language - Reference Manual
	Sep. 1980.