Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]


Groups > comp.lang.c > #13204

Re: Why don't C comments nest?

From Kaz Kylheku <kaz@kylheku.com>
Newsgroups comp.lang.c
Subject Re: Why don't C comments nest?
Date 2011-11-12 21:44 +0000
Organization A noiseless patient Spider
Message-ID <20111112133440.675@kylheku.com> (permalink)
References (8 earlier) <j9lu1a$ft8$1@dont-email.me> <j9m058$sil$1@dont-email.me> <j9mda1$fch$1@dont-email.me> <r7ktb7ddbpsld0uac0sv1daki6cagv9jk1@4ax.com> <j9mm5b$7o5$1@dont-email.me>

Show all headers | View raw


On 2011-11-12, BartC <bc@freeuk.com> wrote:
> "Robert Wessel" <robertwessel2@yahoo.com> wrote in message
>> "6.4.9 Comments
>> Except within a character constant, a string literal, or a comment,
>> the characters /* introduce a comment. The contents of such a comment
>> are examined only to identify multibyte characters and to find the
>> characters */ that terminate it."
>
> In other words, anything is allowed, including source code, of C or anything
> else.

No, because the formal language allowed within the comment excludes the
digraph */ which may occur in the source code of C, inside a string
literal, as part of a comment, or inside a // comment.

> So the suggestion that comments shouldn't contain source code is a style
> issue that shouldn't be the concern of the Standard or imposed by a
> compiler.

It's more than a style issue; it's a formal language issue. Comments can only
contain a subset of the possible set of C strings.

It is useful that you can have a subset of C within comments, for instance,
coding examples. They just can't have /*...*/ comments of their own, which is
fine since they are already inside a comment which can explain everything.

A mechanism for commenting out arbitrary code must be robust, period. This way
it can be applied to a 50,000 line piece of source code without worry that
anything breaks. 

#if 0 ... #endif  satisfies that requirement. 

For excluding small ranges of text not confined entire lines,
a variadic macro which expands to nothing works great:

  #define IG(...) 
  IG(abitrary * preprocessor, ++t 0kens)

Therefore, it is no longer necessary to entertain proposals about nested
comments.

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread


Thread

Why don't C comments nest? Aron Packer <atp1@rightthing.invalid> - 2011-11-11 19:21 +0000
  Re: Why don't C comments nest? James Kuyper <jameskuyper@verizon.net> - 2011-11-11 14:31 -0500
    Re: Why don't C comments nest? Noob <root@127.0.0.1> - 2011-11-17 11:21 +0100
      Re: Why don't C comments nest? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-11-18 15:55 +0200
  Re: Why don't C comments nest? nroberts <roberts.noah@gmail.com> - 2011-11-11 11:25 -0800
  Re: Why don't C comments nest? Kaz Kylheku <kaz@kylheku.com> - 2011-11-11 20:11 +0000
    Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-11 20:28 +0000
      Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-11 13:16 -0800
        Re: Why don't C comments nest? James Kuyper <jameskuyper@verizon.net> - 2011-11-11 16:28 -0500
          Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-11 13:54 -0800
            Re: Why don't C comments nest? Willem <willem@toad.stack.nl> - 2011-11-12 12:07 +0000
              Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-12 13:11 -0800
                Re: Why don't C comments nest? Willem <willem@toad.stack.nl> - 2011-11-12 22:29 +0000
                Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-12 16:36 -0800
                Re: Why don't C comments nest? Willem <willem@toad.stack.nl> - 2011-11-13 10:30 +0000
                Re: Why don't C comments nest? James Kuyper <jameskuyper@verizon.net> - 2011-11-13 06:31 -0500
                Re: Why don't C comments nest? Willem <willem@toad.stack.nl> - 2011-11-13 16:57 +0000
            Re: Why don't C comments nest? Stephen Sprunk <stephen@sprunk.org> - 2011-11-12 08:21 -0600
              Re: Why don't C comments nest? Lauri Alanko <la@iki.fi> - 2011-11-12 14:29 +0000
                Re: Why don't C comments nest? Acid Washed China Blue Jeans <chine.bleu@yahoo.com> - 2011-11-12 06:57 -0800
                Re: Why don't C comments nest? Kaz Kylheku <kaz@kylheku.com> - 2011-11-12 17:51 +0000
              Re: Why don't C comments nest? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-12 09:44 -0500
                Re: Why don't C comments nest? Stephen Sprunk <stephen@sprunk.org> - 2011-11-12 16:37 -0600
            Re: Why don't C comments nest? Kenneth Brody <kenbrody@spamcop.net> - 2011-11-15 14:22 -0500
              Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-16 08:41 +1300
                Re: Why don't C comments nest? James Kuyper <jameskuyper@verizon.net> - 2011-11-15 14:48 -0500
                Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-16 09:03 +1300
                Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-15 20:37 +0000
                Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-16 10:06 +1300
                Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-15 14:31 -0800
                Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-15 22:41 +0000
                Re: Why don't C comments nest? Kaz Kylheku <kaz@kylheku.com> - 2011-11-15 23:06 +0000
                Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-15 23:58 +0000
                Re: Why don't C comments nest? Kaz Kylheku <kaz@kylheku.com> - 2011-11-16 01:58 +0000
                Re: Why don't C comments nest? Willem <willem@toad.stack.nl> - 2011-11-15 22:40 +0000
                Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-16 11:48 +1300
                Re: Why don't C comments nest? Kaz Kylheku <kaz@kylheku.com> - 2011-11-15 23:13 +0000
                Re: Why don't C comments nest? Kenneth Brody <kenbrody@spamcop.net> - 2011-11-16 12:57 -0500
                Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-17 07:42 +1300
                Re: Why don't C comments nest? John Gordon <gordon@panix.com> - 2011-11-16 18:57 +0000
                Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-17 08:48 +1300
                Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-16 11:50 -0800
                Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-17 09:00 +1300
                Re: Why don't C comments nest? Kaz Kylheku <kaz@kylheku.com> - 2011-11-16 20:20 +0000
                Re: Why don't C comments nest? blp@cs.stanford.edu (Ben Pfaff) - 2011-11-16 11:57 -0800
                Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-17 09:47 +1300
                Re: Why don't C comments nest? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-11-18 15:49 +0200
                Re: Why don't C comments nest? James Kuyper <jameskuyper@verizon.net> - 2011-11-18 10:15 -0500
                Re: Why don't C comments nest? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-11-18 17:57 +0200
        Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-11 22:14 +0000
          Re: Why don't C comments nest? blp@cs.stanford.edu (Ben Pfaff) - 2011-11-11 14:35 -0800
            Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 00:10 +0000
          Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-11 15:14 -0800
            Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 00:37 +0000
          Re: Why don't C comments nest? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-11 20:21 -0500
            Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 11:10 +0000
              Re: Why don't C comments nest? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-12 08:11 -0500
                Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 13:57 +0000
                Re: Why don't C comments nest? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-12 09:34 -0500
                Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 18:17 +0000
                Re: Why don't C comments nest? Robert Wessel <robertwessel2@yahoo.com> - 2011-11-12 14:09 -0600
                Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 20:49 +0000
                Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-12 13:42 -0800
                Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 21:53 +0000
                Re: Why don't C comments nest? Kaz Kylheku <kaz@kylheku.com> - 2011-11-12 21:44 +0000
                Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 22:12 +0000
                Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-13 11:22 +1300
                Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-12 16:32 -0800
                Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-12 13:09 -0800
                Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 21:46 +0000
                Re: Why don't C comments nest? Seebs <usenet-nospam@seebs.net> - 2011-11-12 21:40 +0000
      Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-12 11:20 +1300
      Re: Why don't C comments nest? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-11-12 00:40 +0200
      Re: Why don't C comments nest? Kaz Kylheku <kaz@kylheku.com> - 2011-11-12 04:29 +0000
        Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 10:54 +0000
          Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-13 09:11 +1300
            Re: Why don't C comments nest? "BartC" <bc@freeuk.com> - 2011-11-12 20:52 +0000
              Re: Why don't C comments nest? Ian Collins <ian-news@hotmail.com> - 2011-11-13 10:22 +1300
              Re: Why don't C comments nest? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-11-13 23:55 +0200
        Re: Why don't C comments nest? Acid Washed China Blue Jeans <chine.bleu@yahoo.com> - 2011-11-12 07:02 -0800
          Re: Why don't C comments nest? Keith Thompson <kst-u@mib.org> - 2011-11-12 13:13 -0800
            Re: Why don't C comments nest? Acid Washed China Blue Jeans <chine.bleu@yahoo.com> - 2011-11-12 13:48 -0800
  Re: Why don't C comments nest? Acid Washed China Blue Jeans <chine.bleu@yahoo.com> - 2011-11-11 16:51 -0800
  Re: Why don't C comments nest? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-11-12 22:55 +0000
  Re: Why don't C comments nest? Kenneth Brody <kenbrody@spamcop.net> - 2011-11-15 14:17 -0500

csiph-web