Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!pasteur!ucbvax!hplabs!sdcrdcf!ism780c!haddock!karl
From: karl@haddock.ISC.COM (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: trigraphs in X3J11
Message-ID: <4189@haddock.ISC.COM>
Date: 24 May 88 22:28:14 GMT
References: <5215@ico.ISC.COM> <10949@apple.Apple.Com>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 31

In article <10949@apple.Apple.Com> lenoil@apple.UUCP (Robert Lenoil) writes:
>Instead of introducing [trigraphs], why not simply extend the backslash
>escape mechanism to be valid outside of strings?

That's an easy one: backslash is one of the characters that may not exist!

>This would allow the use of #defines
>#define ??< \173	/* open brace */
>#define ??> \175	/* close brace */

Not unless you extend the preprocessor's notion of what constitutes a valid
macro name.  Note also that the magic constants \173 and \175 are unportable.

In article <10941@steinmetz.ge.com> davidsen@steinmetz.ge.com (William E. Davidsen Jr) writes:
>I scanned my local source directory and found three programs of 102 which
>would break. ... I did NOT scan the directory of programs which do device
>control, since I have made that point and every one would break and have to
>be handcoded with escape sequences, etc, do get by this.

Are you sure you have that many programs that would break?  Note that `??'
alone is not a problem; it becomes a trigraph only when followed by one of the
nine characters "=(/)'<!>-".  (Unlike backslash, which is reserved even if the
following character is unrecognized.)

Assuming trigraphs stay in, the fix is simple: filter your code through
	sed -e "s;??\\([-=(/)'<!>]\\);?\\\\?\\1;g"
as part of the ANSIfication process.  (Better yet, do it now before you run
into a compiler with trigraphs.  It won't hurt, unless your current compiler
complains about the unrecognized escape "\?".)

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint