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From: karl@haddock.ISC.COM (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: Switch statements
Message-ID: <1078@haddock.ISC.COM>
Date: Wed, 9-Sep-87 12:54:07 EDT
Article-I.D.: haddock.1078
Posted: Wed Sep  9 12:54:07 1987
Date-Received: Fri, 11-Sep-87 04:34:05 EDT
References: <855@tjalk.cs.vu.nl> <2683@hoptoad.uucp>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 26

In article <2347@mmintl.UUCP> franka@mmintl.UUCP (Frank Adams) writes:
>One occasional problem with C, which does not fit with the overall language
>philosophy, is that a range check is always[1] implicit in a switch
>statement.  If the statement happens to be at a key place in the code, a not
>unusual occurrence, this can add significantly to running time.
>
>Does anyone have any suggestions for a good syntax to indicate to the
>compiler that this check is not desired; that if the discriminant is not one
>of the specified cases, the result of the switch is to be undefined?

How about "#pragma nodefault"?

I've noticed this too, but (unlike you) I don't think it would be such a bad
thing if this were the default behavior.  Learning to "always" add the line
"default: break;" isn't any harder than remembering to "always" have break
statements between cases.  (Not to say that two wrongs make a right -- I'm
just trying to prebut the argument that novice users wouldn't be able to cope
with it.)

Moreover, PASCAL -- one of the languages to which C is oft compared, and often
the only previous structured language known to a new C user -- has this same
attribute.  (It's true that PASCAL's case statement is crippled beyond
usefulness, but that's because there's no way to override this behavior.  This
would not be the case in the hypothetical modified C.)

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