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From: dietz%slb-doll.csnet@CSNET-RELAY.ARPA (Paul Dietz)
Newsgroups: net.lang.c
Subject: What happened to label variables?
Message-ID: <1418@brl-smoke.ARPA>
Date: Fri, 28-Feb-86 18:06:51 EST
Article-I.D.: brl-smok.1418
Posted: Fri Feb 28 18:06:51 1986
Date-Received: Mon, 3-Mar-86 00:35:44 EST
Sender: news@brl-smoke.ARPA
Lines: 28

I recall that C on early UNIX's treated labels as constants of type
(int *).  As a result, you could assign labels to variables and even
jump to the label in a variable.  This got taken out of K&R, and
as I far as I can tell it's not in other C's today.

This is unfortunate; I ran into a situation recently in which I wanted
to (automatically) generate C code that should, for efficiency reasons,
contain label variables.  I had to simulate them with a switch statement
of the form:

	switch(labelindex) {
		case 1: goto label1;
		case 2: goto label2;
		...
		case n: goto labeln;
		default: fprintf(stderr,"unknown label index: %d\n",
					labelindex);
			 abort();
	}

This is a lot slower, though, and some of the compiler's I tried it
on (the VAX VMS C compiler, for example) did not peephole optimize the
jump table implementing the switch and the branch instructions
implementing the goto's (this should have been treated as a jump
to a jump).

I'm curious if any commerically available C compilers implement jumps
to arbitrary pointers without recourse to assembly language inserts.