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From: bet@ecsvax.UUCP
Newsgroups: net.lang.c
Subject: Re: Using &LABEL
Message-ID: <3185@ecsvax.UUCP>
Date: Fri, 31-Aug-84 15:00:12 EDT
Article-I.D.: ecsvax.3185
Posted: Fri Aug 31 15:00:12 1984
Date-Received: Mon, 3-Sep-84 11:41:27 EDT
References: decwrl.3480
Lines: 34

This brings up my only *major* complaint with C -- the weakness of its
handling of labels. The question

>>	Finally, is &LABEL an officially sanctioned K&R construct?  I don't
>> have my copy with me so I can't look it up right now...

is pretty easy (I think): From the C Reference manual, in the back of
K&R, section 9.12:
	... The only use of a label is as a target of a goto. ...

(You can take my word that this isn't an unreasonably out-of-context
quote). Many compilers, however, as an accident of implementation, give
the address in the code space when you use &label, allow you to assign
that to a variable of suitable size (int often works) and branch to
it.  HOWEVER, this is flagrantly illegal and non-portable. The
definition of C prohibits it. So here goes my desired extention to C:

Make 'label' be a data type. Consider "<identifier> :" to be a
constant, allow label variables to be created, and in particular arrays
of labels.  Voila: jump tables! Many (most) uses of goto <label> might
be unstructured, or even UGLY. However, one particular construct occurs
reasonably often in a kind of programming C is good at: implementing
compilers and suchlike text processors. This construct is the finite
state automaton. What you really want to implement one efficiently is a
label array, for "goto array[input]" to be a state transition.

It seems to me that this treatment of "label" wouldn't conflict with the
existing definition of C, and in fact would formally bless a "feature"
that some compilers already have. I am grateful, at least, that the
philosophy in designing a C compiler is to make it do everything that C
requires, but not necessarily to prohibit everything C prohibits. LONG
LIVE LINT!!!
					Bennett Todd
					...{decvax,ihnp4,akgua}!mcnc!ecsvax!bet