Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!mailrus!cornell!uw-beaver!uw-june!pardo
From: pardo@june.cs.washington.edu (David Keppel)
Newsgroups: comp.lang.c
Subject: Must the "switch" quantity be an integer?
Summary: Barfs on switch((foo_t*)i) { ... }
Message-ID: <6137@june.cs.washington.edu>
Date: 19 Oct 88 19:23:25 GMT
Reply-To: pardo@cs.washington.edu (David Keppel)
Organization: U of Washington, Computer Science, Seattle
Lines: 51

[ appologies if this was just discussed ]

I want to declare a bunch of "magic" pointers, e.g., as is done in
/usr/include/signal.h:

    #define	BUFPTR		((os_t *)1)
    #define	SPTR		((os_t *)2)
     :

And do things like:

    foo[0] = BUFPTR;
    foo[1] = (os_t *) malloc (sizeof(os_t));
     :

then:

    switch (foo[i]) {
	case BUFPTR:
	    /* handle magic case #1 */
	    break;
	case SPTR:
	    /* handle magic case #2 */
	    break;
	case ...
	 :
	 :
	default:
	    normal (foo[i]);
    }

When I compile this with pcc, everything is happy.
When I compile this with gcc and turn on all of the
flags for dpANS (-ansi, -pedantic), the compiler
refuses to accept the code since "switch quantity is
not an integer".  This *is* certainly true, but isn't
what I expected.  I wasn't aware that dpANS required
the switch quantity to be an integer (or, presumably
things such as chars that can be converted to integers
implicitly).

Two questions:
(a) What are the rules?
(b) Can I do this portably without using a mass of
    if (foo[i]==BUFPTR) { ... } else if (foo[i]==SPTR)...
    code?  (Or, "*can* I do this portably?")

	    ;-D on  ( Compilo ad adsurd-bum )  Pardo
-- 
		    pardo@cs.washington.edu
    {rutgers,cornell,ucsd,ubc-cs,tektronix}!uw-beaver!june!pardo