benny@techunix.BITNET (Benny Pinkas) (09/14/88)
Can I use the Preprocessor to define a comment?
I mean something like:
#define COM /*this is a comment*/
or even
#define STARTCOM /*
Usually the text after the /* is considered as a comment and is not part
of the macro definition.
I searched a dozen of C books, and didn't find something of help.
Thanks in advance
Bennychris@mimsy.UUCP (Chris Torek) (09/14/88)
In article <5438@techunix.BITNET> benny@techunix.BITNET (Benny Pinkas) writes: >Can I use the Preprocessor to define a comment? >#define COM /*this is a comment*/ This is legal; it is merely useless. >or even >#define STARTCOM /* This is rather dubious. >Usually the text after the /* is considered as a comment and is not part >of the macro definition. Why should you care? You cannot (portably) view the text (if any) emitted by the preprocessor, which may well be an integral part of the compiler. -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@mimsy.umd.edu Path: uunet!mimsy!chris
henry@utzoo.uucp (Henry Spencer) (09/14/88)
In article <5438@techunix.BITNET> benny%techunix.bitnet@jade.berkeley.edu (Benny Pinkas) writes: >Can I use the Preprocessor to define a comment? Well, maybe. The draft standard unambiguously says "no": comments are scanned and deleted before preprocessing is done. However, many existing implementations do things differently. The preprocessor semantics were never very well specified. Given that most implementations will comply with, or at least move towards, ANSI compliance eventually, you should not rely on it. >#define COM /*this is a comment*/ This ends up defining COM to be white space, which is legitimate. >#define STARTCOM /* This isn't going to work. -- NASA is into artificial | Henry Spencer at U of Toronto Zoology stupidity. - Jerry Pournelle | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
paulb@ttidca.TTI.COM (Paul Blumstein) (09/14/88)
In article <5438@techunix.BITNET> benny%techunix.bitnet@jade.berkeley.edu (Benny Pinkas) writes:
+Can I use the Preprocessor to define a comment?
+I mean something like:
+#define COM /*this is a comment*/
+or even
+#define STARTCOM /*
+
+Usually the text after the /* is considered as a comment and is not part
+of the macro definition.
+I searched a dozen of C books, and didn't find something of help.
Perhaps, If you told us what you want to do exactly, we can be of more
help. Why define a comment, when it is already defined?
If you wanted a whole block commented out, one technique is:
#ifdef COMMENT
...
#endif
or
#if 0
...
#endif
=============================================================================
Paul Blumstein | "Life is what is happening while you are
Citicorp/TTI | busy making other plans" -- John Lennon
Santa Monica, CA +-------------------------------------------------
{philabs,csun,psivax}!ttidca!paulb or paulb@ttidca.TTI.COM
If caught, the Secretary of Citicorp will disavow all knowlege of my actions.bill@proxftl.UUCP (T. William Wells) (09/15/88)
In article <5438@techunix.BITNET> benny%techunix.bitnet@jade.berkeley.edu (Benny Pinkas) writes:
: Can I use the Preprocessor to define a comment?
No.
---
Bill
novavax!proxftl!billlbr@holos0.UUCP (Len Reed) (09/15/88)
From article <13544@mimsy.UUCP>, by chris@mimsy.UUCP (Chris Torek): > In article <5438@techunix.BITNET> benny@techunix.BITNET (Benny Pinkas) writes: >>Can I use the Preprocessor to define a comment? > >>#define STARTCOM /* > > This is rather dubious. > >>Usually the text after the /* is considered as a comment and is not part >>of the macro definition. > > Why should you care? You cannot (portably) view the text (if any) emitted > by the preprocessor, which may well be an integral part of the compiler. You misunderstand. On Xenix and MSC 5.x (where I've tried this) consider: #define COMMENT /* #define CLOSE_COMMENT */ The pre-processor considers these two lines to be functionally equivalent to the single line: #define COMMENT /* #define CLOSE_COMMENT */ which is no different than #define COMMENT This is because comment structures are parsed in the 1st pass before #defines. Comments are not stored in the pre-processor lookup table. Later when you say: COMMENT A whole bunch of stuff CLOSE_COMMENT the compiler tries to compile A whole bunch of stuff CLOSE_COMMENT and messes up. -- - Len Reed
will.summers@p6.f18.n114.z1.fidonet.org (will summers) (09/17/88)
Len Reed writes: >Can I use the Preprocessor to define a comment? > >#define STARTCOM /* No. (you were talking about ANSI right?). To resolve ambiguities ANSI defines "translation phases" that function as-if they are separate passes over the source file. Comments get replaced by a single whitespace character in "pass" 3; preprocessing directives in "pass" 4. > #define COMMENT /* > #define CLOSE_COMMENT */ > > The pre-processor considers these two lines to be functionally equivalent > to the single line: > > #define COMMENT /* #define CLOSE_COMMENT */ Yup. > which is no different than > #define COMMENT Which is precisely what "pass" 4 sees. > COMMENT > A whole bunch of stuff > CLOSE_COMMENT Try: #define COMMENT 0 #if COMMENT A whold bunch of stuff #endif /* CLOSE_COMMENT */ One might be tempted to: #define COMMENT #if 0 #define CLOSE_COMMENT #endif But ANSI (Jan '88 draft) says 3.8.3.4 Rescanning and further replacement ... The resulting completely macro-replaced preprocessing token sequence is not processed as a preprocessing directive even if it resembles one. #if 0 may not be pleasing to your sense of aesthetics, but it is a well recognized C idiom. Use it for a while and COMMENT CLOSE_COMMENT is likely to become as alien to your eye as #if 0 is now... If you are adament: write the code as you wish and run it add a trivial pre-compile pass that maps COMMENT to #if 0 to the compile script. \/\/ill <tm> -- St. Joseph's Hospital/Medical Center - Usenet <=> FidoNet Gateway Uucp: ...{gatech,ames,rutgers}!ncar!noao!asuvax!stjhmc!18.6!will.summers
bill@proxftl.UUCP (T. William Wells) (09/17/88)
In article <13544@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
: >#define STARTCOM /*
:
: This is rather dubious.
We use this construction in our code, it is always in something
like:
#define XYZZY /* comment ....
more comment */
We have never had any complaints about it.
I'd say that
#define STARTCOM /*
just defines STARTCOM as nothing and comments out anything
following the #define.
I'd also say that any compiler that didn't do this is broken.
---
Bill
novavax!proxftl!billchris@mimsy.UUCP (Chris Torek) (09/18/88)
>In article <13544@mimsy.UUCP> I wrote: >: >#define STARTCOM /* >: >: This is rather dubious. In article <779@proxftl.UUCP>, bill@proxftl.UUCP (T. William Wells) writes: >I'd say that > >#define STARTCOM /* > >just defines STARTCOM as nothing and comments out anything >following the #define. > >I'd also say that any compiler that didn't do this is broken. Indeed, that is what it must do. What was missing from <5438@techunix.BITNET> that prompted my `dubious' was any surrounding context. I got the impression that the intent might be to create a macro that acted like an open-comment `/*' pair, e.g., #define TNEMMOC */ #define COMMENT /* COMMENT text to be commented out TNEMMOC code which of course does not work. -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@mimsy.umd.edu Path: uunet!mimsy!chris
mh@wlbr.EATON.COM (Mike Hoegeman) (09/19/88)
In article <3999@bsu-cs.UUCP> dhesi@bsu-cs.UUCP (Rahul Dhesi) writes: >In article <13604@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes: >> COMMENT >> text to be commented out >> TNEMMOC >> code >>which of course does not work. >Well...this may be just nitpicking, but: > #define COMMENT "/*" > #define TNEMMOC "*/" > COMMENT > text to be commented out > TNEMMOC /* sdrawkcab "tnemmoc" tsuj si siht */ > c code >Then use the preprocessor *twice* and you get > c code >Which is now ready for compilation. Maybe I'm missing something here but what the h*ll is wrong with plain old /******** ********/ Sheesh!! -mike
friedl@vsi.UUCP (Stephen J. Friedl) (09/19/88)
In article <5438@techunix.BITNET>, benny@techunix.BITNET (Benny Pinkas) writes: > > Can I use the Preprocessor to define a comment? I mean something like: > I'm surprised nobody posted this. Benny didn't ask about a portable solution :-), so try this: # define STARTCOM //**/* # define ENDCOM */**// This is specifically disallowed by the dpANS, it is not available everywhere, and it is definitely not something to use for any reason other than curiosity. This is intended as a curiosity only. Steve -- Steve Friedl V-Systems, Inc. +1 714 545 6442 3B2-kind-of-guy friedl@vsi.com {backbones}!vsi.com!friedl attmail!vsi!friedl ------------Nancy Reagan on conductance: "Just say mho"------------
peter@ficc.uu.net (Peter da Silva) (09/19/88)
In article <3999@bsu-cs.UUCP>, dhesi@bsu-cs.UUCP (Rahul Dhesi) writes: > It is agreed that a Real ANSI-conforming C compiler might not supply a > separate preprocessor pass, but who cares? Such a C compiler would be > an instant commercial failure. Bzzzt! There are quite a few compilers with built-in preprocessors that are not commercial failures. I don't like this any better than you but like split I&D and income tax it's nothing that we can do anything about. I'm just glad that the compiler I use at home still has a seperate assembler pass. -- Peter da Silva `-_-' Ferranti International Controls Corporation. "Have you hugged U your wolf today?" peter@ficc.uu.net
will.summers@p6.f18.n114.z1.fidonet.org (will summers) (09/20/88)
> Date: 18 Sep 88 18:25:27 GMT > Organization: Eaton IMSD, Westlake Village, CA In article <23345@wlbr.EATON.COM> mh@wlbr.EATON.COM (Mike Hoegeman) writes: > >In article <13604@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes: > >> COMMENT > >> text to be commented out > >> TNEMMOC > >> code > >>which of course does not work. > Maybe I'm missing something here but what the h*ll is wrong with > plain old > > /******** > > ********/ > > Sheesh!! It fails to "comment out" text with "/*" or "*/" tokens. Like in text derived from commented code. Otherwise in my mind /********************** or /*---------- is perferable. \/\/ill <tm> -- St. Joseph's Hospital/Medical Center - Usenet <=> FidoNet Gateway Uucp: ...{gatech,ames,rutgers}!ncar!noao!asuvax!stjhmc!18.6!will.summers
friedl@vsi.UUCP (Stephen J. Friedl) (09/22/88)
In article <5438@techunix.BITNET>, benny@techunix.BITNET (Benny Pinkas) writes: > > Can I use the Preprocessor to define a comment? I mean something like: > Then, in article <844@vsi.UUCP>, friedl@vsi.UUCP (*me*) writes: > I'm surprised nobody posted this, > > # define STARTCOM //**/* > # define ENDCOM */**// I'll be durned, it doesn't work. The first part does indeed define STARTCOM to be /*, but I thought that once the STARTCOM was replaced by /*, it would pass it onto the compiler unchanged (the compiler accepts the same comment notation as cpp). Apparently, however, it rescans this at cpp-time and the ENDCOM is never macro-expanded. I could have sworn I did this once, and I suspect that a maniac with cpp could probably find a way to do this, but I couldn't. Thanks to Don Seeley at U-of-Utah for throwing the egg on my face :-). -- Steve Friedl V-Systems, Inc. +1 714 545 6442 3B2-kind-of-guy friedl@vsi.com {backbones}!vsi.com!friedl attmail!vsi!friedl ------------Nancy Reagan on conductance: "Just say mho"------------
vopata@ksuvax1.cis.ksu.edu (Ed Vopata) (09/23/88)
In article <855@vsi.UUCP> friedl@vsi.UUCP (Stephen J. Friedl) writes: >In article <5438@techunix.BITNET>, benny@techunix.BITNET (Benny Pinkas) writes: >> >> Can I use the Preprocessor to define a comment? I mean something like: >> Yes! The following in a sample program which will demonstrate the use of STARTCOM and ENDCOM macros for defining the beginning and ending of a C Comment. Also included is the output of the preprocessor (cc -E). I have compiled this program on a couple of C compilers (one provided with 4.3 BSD and one provided by AT&T) and the program works. Please note that in the "#define STAR *" there must be only 1 space between the "STAR" and the "*" otherwise STARTCOM may look like "/ *". ------- cut here ------- #define STAR * #define STARTCOM /STAR #define ENDCOM STAR/ STARTCOM Comment.c -- by Edward Vopata (9/22/88) Put the text of the comment here. Multiple lines are allowed. ENDCOM main() { STARTCOM Some Comments within the main program ENDCOM } ------- cut here ------- The following is the ouput of the C preprocessor. % cc -E comment.c # 1 "comment.c" /* Comment.c -- by Edward Vopata (9/22/88) Put the text of the comment here. Multiple lines are allowed. */ main() { /* Some Comments within the main program */ } ---------- Name : Edward Vopata Dept. of Computing & Information Sciences Internet : vopata@ksuvax1.cis.ksu.edu Kansas State University Bitnet : vopata@ksuvax1.BITNET Manhattan, Kansas UUCP : {pyramid,ucsd}!ncr-sd!ncrwic!ksuvax1!vopata (913) 532-6350
sar@datcon.UUCP (Simon A Reap) (09/23/88)
In article <768@proxftl.UUCP> bill@proxftl.UUCP (T. William Wells) writes: >In article <5438@techunix.BITNET> benny%techunix.bitnet@jade.berkeley.edu (Benny Pinkas) writes: >: Can I use the Preprocessor to define a comment? > >No. > >--- >Bill >novavax!proxftl!bill Pyramid C (at least) says "Comments? Don't just say no!' How about... #define ASTERISK * #define SCOM /ASTERISK #define ECOM ASTERISK/ #define PUTCOMM(a) SCOM a ECOM Then, as sample code..... start comment is SCOM end comment is ECOM comment here -> PUTCOMM(will be inside a comment) Which produces (at least on a Pyramid, using OSx4.0, in both the att and ucb universes, with blanks and other detritus removed for brevity)... start comment is /* end comment is */ comment here -> /* will be inside a comment */ I *can* see a use for this. You may just want to use the pre-processor part of cc to produce commented output (yes, I know one should use 'm4' for this, but 'better the devil you know...' :^). Good luck, Benny! -- Enjoy, yerluvinunclesimon Opinions are mine - I don't even have a cat Reach me at sar@datcon.co.uk, or ...!mcvax!ukc!pyrltd!datcon!sar
henry@utzoo.uucp (Henry Spencer) (09/24/88)
In article <855@vsi.UUCP> friedl@vsi.UUCP (Stephen J. Friedl) writes: >> # define STARTCOM //**/* >I'll be durned, it doesn't work. The first part does indeed >define STARTCOM to be /*... You can't depend on this, I'm afraid. In fact, it is not true in ANSI C: the /**/ comment turns into a space, not into nothing. -- NASA is into artificial | Henry Spencer at U of Toronto Zoology stupidity. - Jerry Pournelle | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
henry@utzoo.uucp (Henry Spencer) (09/24/88)
In article <678@ksuvax1.cis.ksu.edu> vopata@ksuvax1.cis.ksu.edu (Ed Vopata) writes: >Yes! The following in a sample program which will demonstrate the use of >STARTCOM and ENDCOM macros for defining the beginning and ending of a C >Comment. Also included is the output of the preprocessor (cc -E). I have >compiled this program on a couple of C compilers (one provided with 4.3 BSD >and one provided by AT&T) and the program works. It would probably work with any compiler using the Reiser preprocessor, which is used by most Unix compilers (and, in particular, by essentially all PCC-derived compilers). It won't necessarily work with brand-X preprocessors. I'll say it again, just in case it didn't penetrate the first time: there is *no* portable way to do this. In particular, doing it in ANSI C is fundamentally impossible, because comment stripping precedes preprocessing. (One of X3J11's more laudable, and simultaneously more difficult, feats was to actually make questions like this easy to answer!) -- NASA is into artificial | Henry Spencer at U of Toronto Zoology stupidity. - Jerry Pournelle | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
will.summers@p6.f18.n114.z1.fidonet.org (will summers) (09/24/88)
In article <678@ksuvax1.cis.ksu.edu> vopata@ksuvax1.cis.ksu.edu (Ed Vopata) writes: > In article <855@vsi.UUCP> friedl@vsi.UUCP (Stephen J. Friedl) writes: > The following in a sample program which will demonstrate the use of > STARTCOM and ENDCOM macros for defining the beginning and ending of a C > Comment. ... I have > compiled this program on a couple of C compilers (one provided with 4.3 BSD > and one provided by AT&T) and the program works. > > Please note that in the "#define STAR *" there must be only 1 space between > the "STAR" and the "*" otherwise STARTCOM may look like "/ *". > > ------- cut here ------- > #define STAR * > #define STARTCOM /STAR > #define ENDCOM STAR/ > > STARTCOM > Comment.c -- by Edward Vopata (9/22/88) > > Put the text of the comment here. > Multiple lines are allowed. > ENDCOM Interesting... Will it always work under dpANS? (I doubt it). Even though the code will look like /* < comments > */ after translation phase 4, subsequent translation phases need not interpret this as a comment: they expect comments to have been stripped. (2.1.1.2) On second thought "need not" may not be strong enough: perhaps it should be "subsequent translation phases **may not** interpret this as a comment". Since STARTCOM..ENDCOM will generate code with syntax errors, a conforming implementation -must- issue a diagnostic message. (2.1.1.3) As long as a "preprocess only" option is available, however, running the code through -twice- would seem to work under dpANS... But then a simpler pre-compile pass can map STARTCOM to /* if desired. dpANS aside, STARTCOM..ENDCOM seems non-portable unless the order of macro-expansion/comment-striping is specified somewhere pre-ANSI. It does not seem to have been specified in K&Rv1. \/\/ill -- St. Joseph's Hospital/Medical Center - Usenet <=> FidoNet Gateway Uucp: ...{gatech,ames,rutgers}!ncar!noao!asuvax!stjhmc!18.6!will.summers
nagel@paris.ics.uci.edu (Mark Nagel) (09/25/88)
In article <24@datcon.UUCP> sar@datcon.co.uk (Simon A Reap) writes: | |How about... | #define ASTERISK * | #define SCOM /ASTERISK | #define ECOM ASTERISK/ | #define PUTCOMM(a) SCOM a ECOM | |Then, as sample code..... | start comment is SCOM | end comment is ECOM | comment here -> PUTCOMM(will be inside a comment) | |Which produces (at least on a Pyramid, using OSx4.0, in both the att |and ucb universes, with blanks and other detritus removed for brevity)... | start comment is /* | end comment is */ | comment here -> /* will be inside a comment */ | |I *can* see a use for this. You may just want to use the pre-processor |part of cc to produce commented output (yes, I know one should use 'm4' |for this, but 'better the devil you know...' :^). I can see all sorts of problems from this. Why in the world is everyone so hot to redefine the comment tokens? I can just see it now: SCOM Add 1 to foo foo++; ECOM and then later in development... SCOM Add 1 to foo foo++; /* foo controls the register bar */ ECOM Hmm. Why is my code blowing up? -- Mark Nagel Department of Information and Computer Science, UC Irvine nagel@ics.uci.edu (ARPA) When they ship styrofoam... {sdcsvax|ucbvax}!ucivax!nagel (UUCP) ...what do they pack it in?
karl@haddock.ima.isc.com (Karl Heuer) (09/27/88)
No, there is no legal way in ANSI C (or in K&R C, according to K&R) to "define a comment". Yes, you can trick the Reiser cpp into doing it anyway. Except for the Obfuscated C Contest, there is little reason to want to do so. If you're trying to suppress code which contains comments, the appropriate notation is "#if 0" ... "#endif". (Or, if your preprocessor is so backward as to not have #if, "#ifdef notdef" ... "#endif" will do.) Generally, you should use /* ... */ for natural language commentary, and #if to remove code. Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint