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From: shankar@hpclscu.HP.COM (Shankar Unni)
Newsgroups: comp.lang.c++
Subject: Re: "//" comments and #define's : problems
Message-ID: <1000020@hpclscu.HP.COM>
Date: 12 Jul 89 20:27:56 GMT
References: <1000019@hpclscu.HP.COM>
Organization: Hewlett-Packard Calif. Language Lab
Lines: 34

> When fixing up a "cpp" to handle "//"-style comments, I came across an
> interesting problem.

I've already received several messages pointing out page 130 of the Bible
to me.

I guess my reading of that part of the book was a little perfunctory.
However, after reading that page, I'm still uncomfortable with it. What
that page is trying to do is treat the preprocessing phase as something
separate from the C++ language, and cramming the C preprocessing semantics
down the throat of C++ (since the C language does not have "//" comments,
let's make them work only on the lines unaffected by the preprocessor..).

The first thing we need to do is to look at the whole setup in a unified
fashion. Either macros and ifdef's are in the language, or they are not.
If they are, then the preprocessing phase is an essential part of the
language, and should work coherently with the other aspects of the
language, like "//" comments. If they are not, then that fact should be
mentioned explicitly up front. Since they are mentioned in pages 129 and
130, and also in sec 7.3.5 (generic classes), I assume that they are part
of the language.

It does not take a great effort to define precise semantics for the
preprocessing phase. For instance, in ANSI C, the precise semantics are
defined in sections 2.1.1.2 (translation phases) and 3.7 (preprocessor
directives). Incidentally, in the ANSI standard, the comments are stripped
from the macro replacement text UP FRONT (i.e. even before processing the
#define directive), so page 130 of the Bible will have to change a bit.

What do you say?
-----
Shankar Unni                                   E-Mail: 
Hewlett-Packard California Language Lab.     Internet: shankar@hpda.hp.com
Phone : (408) 447-5797                           UUCP: ...!hplabs!hpda!shankar