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From: john@frog.UUCP (John Woods, Software)
Newsgroups: comp.lang.c
Subject: Re: Switch statements
Message-ID: <1604@frog.UUCP>
Date: Thu, 10-Sep-87 17:12:00 EDT
Article-I.D.: frog.1604
Posted: Thu Sep 10 17:12:00 1987
Date-Received: Sat, 12-Sep-87 10:49:47 EDT
References: <855@tjalk.cs.vu.nl> <2683@hoptoad.uucp> <916@haddock.ISC.COM> <2347@mmintl.UUCP>
Organization: Superfrog Heaven [ CRDS, Framingham MA ]
Lines: 33

In article <2347@mmintl.UUCP>, franka@mmintl.UUCP (Frank Adams) writes:
#>In article <1022@haddock.ISC.COM> karl@haddock.ima.isc.com (Karl Heuer) writes:
P>>In other words, "case CR, LF:" would have the new semantics, whereas
R>>"case (CR, LF):" would be equivalent to "case LF:".  This is no more
A>>problematic than the current overloading of comma for function calls.
G>
M>Does anyone have any suggestions for a good syntax to indicate to the
A>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?

This seems to be the ideal case of what the ANSI people designed #pragma for.
Before the switch statement you would have the line

#pragma Pretty please, Mr. Compiler, don't check the range on this switch!

and voila! code that's quick if the compiler recognizes the pragma, code
that's correct even if it doesn't.

Perhaps the ANSI committee should give some thought to standardizing certain
"suggested" #pragmas.  (Note: my general feeling about #pragma is similar to
that of the writers of the GNU C compiler, who have the compiler run hack if
it encounters a #pragma line...  If one has to have a 69-way #elseif sequence
to trick innumerable compilers into doing the same thing, what good is it?)

(As it happens, the Greenhills C compiler has a command-line switch to turn
off range checking of switch statements, but it is on a per-file basis, which
seems a tad extreme.)

--
John Woods, Charles River Data Systems, Framingham MA, (617) 626-1101
...!decvax!frog!john, ...!mit-eddie!jfw, jfw@eddie.mit.edu

Maybe it's the sound of a WET RAG hitting a smooth WEASEL!