trigraphs in X3J11

[Karl Heuer]

In article <10949 at apple.Apple.Com> lenoil at 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 at steinmetz.ge.com> davidsen at 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 at haddock.isc.com), The Walking Lint