Hi Paul, ` > >> Hmm, given Bruno's recent point that C89 didn't require ?: support > >> in constant expressions > > I'm skeptical of that. I can't find my copy of the official C89 standard, > but the draft <http://flash-gordon.me.uk/ansi.c.txt> says that > constant expressions can contain ?:. In fact, the grammar in > section 3.4 looks like this: > > constant-expression: > conditional-expression > > and until this discussion I've never heard of the claim that > one cannot use ?: in constant expressions.
Indeed, I cannot find the references that I used on 2002-07-23 when I first used this idiom in gettext/m4/gettext.m4. - The book "C, A reference manual" by Harbison & Steele, section 7.11 "Constant expressions", says: "The binary operators [...] may be used, as may the unary operators - ~ ! The conditional operator ? : may be used ... The original description of C did not mention that the operator ! is allowed in constant expressions, but this was obviously an oversight or typographical error." - <http://www.srcf.ucam.org/~jsm28/gcc/const-exprs-issues.txt> mentions a couple of issues with constant expressions, but not with ? :. Maybe I was confused about '? :' vs. the '!' issue. Maybe I tripped over a GCC bug. But the GCC versions that were current in 2002 are outdated nowadays. Or maybe I tripped over a vendor compiler bug. > Given that (X ? 1 : -1) captures the concept more clearly than > (2 * X - 1), we're better off using the former notation than > the latter. I agree now. Bruno
