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From: shankar@hpclscu.HP.COM (Shankar Unni)
Newsgroups: comp.lang.c++
Subject: Re: "//" comments and #define's : problems
Message-ID: <1000021@hpclscu.HP.COM>
Date: 24 Jul 89 20:20:17 GMT
References: <1000019@hpclscu.HP.COM>
Organization: Hewlett-Packard Calif. Language Lab
Lines: 40

> What about:
>       (d) Insert the carriage return which terminates the comment as well,
>            as in 
> 	x b // comment
> 	y

I'm uncomfortable about this, for a couple of reasons:

  (a) You're overloading the Newline. If you suck up the newline as part
      of the comment, then the #define mechanism should not see the newline.

      Consider, for example,
      
        #define foo bar  /*
	                */
      
      You surely wouldn't treat the embedded newline as a #define terminator.
      In your example, if you treat the newline as part of the comment, then
      you've got the same thing - a newline embedded in a comment, devoid of
      its special properties with respect to #define's. Strictly speaking,
      the preprocessor should then continue on to the next line and tack on
      those tokens onto the expansion list.
      
  (b) Consider, also, tokenizing preprocessors (not the character-based ones
      like the classic /lib/cpp). These preprocessors would convert input
      into discrete tokens (and would convert newlines into a unique,
      white-space-like token so that the #define mechanism would see it
      separately from other whitespace).
      
      If you asked such a preprocessor to suck up the newline as part of
      the "comment" token, it would "lose" the newline (after all, the same
      character cannot be a part of two different tokens).

In fact, the approach that I ended up taking is to strip out "//" comments
from #defines entirely. They will not show up even if "-C" is requested.
It's a minor aesthetic wart, but semantically it's much more satisfying..
-----
Shankar Unni                                   E-Mail: 
Hewlett-Packard California Language Lab.     Internet: shankar@hpda.hp.com
Phone : (408) 447-5797                           UUCP: ...!hplabs!hpda!shankar