Declarations in switches, errors

[Mark Brader]

Actually, there *is* a way to "normally enter" the switch body.
Instead of entering the body by a jump from the switch header, you
put a label on the body itself and jump to that!

	main() {
		int k = 0, m = 0;
		switch (m) bleagh: {
			int j = 4;
		case 0:
			printf ("%d\n", j);
		}
		if (k++ == 0)
			goto bleagh;
	}

Assuming that the implementation doesn't trap on undefined values,
this prints a garbage integer value, then 4.  It would never have
occurred to me to try this, if not for this discussion stream, and I
can't dream of a sensible use for it.  Isn't C wonderful?

Only slightly less bizarre is to put one of the case labels ON the
switch body rather than IN it -- 3.6.4.2 allows this and the compilers
we have here support it -- whereupon you get initialization IF it is
the first case that is chosen.  For instance:

	initj() {printf ("initj() called\n"); return 4;}
	main() {
		int k;
		for (k = 0; k < 3; ++k)
			switch (k)
			case 1:
				{
				int j = initj();
			default:
				printf ("%d\n", j);
			}
	}

Assuming that the implementation doesn't trap on undefined values,
this prints a garbage integer value, "initj() called", 4, and another
garbage integer value.

-- 
Mark Brader		   "I don't care HOW you format   char c; while ((c =
SoftQuad Inc., Toronto	    getchar()) != EOF) putchar(c);   ... this code is a
utzoo!sq!msb, msb at sq.com    bug waiting to happen from the outset." --Doug Gwyn

This article is in the public domain.