Path: utzoo!mnetor!uunet!husc6!sri-unix!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.lang.c
Subject: goto in C (was fallthrough)
Message-ID: <740@cresswell.quintus.UUCP>
Date: 8 Mar 88 00:47:05 GMT
References: <222965b9@ralf.home> <2403@umd5.umd.edu> <25200@cca.CCA.COM> <25348@cca.CCA.COM>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 57
Keywords: C case fallthrough goto

In article <25348@cca.CCA.COM>, g-rh@cca.CCA.COM (Richard Harter) writes:
> Currently I average about one goto per 10,000 lines of code, all of them
> being transfers to a procedure epilog, e.g
> 
> foobaz() {
>   ....
>   allocate space and other setup
>   ....
>   if (some_special_condition) goto wrapup;
>   ....
> wrapup:
>   deallocate space and other cleanup
>   }
> 
> But do people actually use it to any signifigant extent?  Why not just
> drop it?
> -- 

I very often write code of the form

sometype foo()
    {
	int state = 0;

	<side effect 1>	/* open file, or allocate memory */
	state = 1;
	<side effect 2>	/* same sort of thing */
	...
	state = N;
	<return new object>
    ERROR:	
	switch (state) {
	    case N:	/* undo side effect N */
			/* falls through to */
	    case N-1:   ...


	    case 1:	/* undo side effect 1 */
	    case 0:	/* return error code */
	}
    }

If you are trying to write code that other people can use,
it really isn't good manners to lose chunks of memory just
because you couldn't open a file.  One of these per library
package, and one per program, doesn't seem excessive.

This is a sufficiently stylised approach that it could be replaced by
some other mechanism.  (Nested exception handlers?  C++ destructors?
unwind-protect?)  But in a language like C, why not just keep the goto?
{Actually, a break-from-labelled-statement would work too, but that's
just another goto.}

There's another reason for retaining the goto.  Look at the output of
YACC some time.  I counted five labels in yyparse(), but may have
missed some.  It isn't just people who write C, you know!  Why shouldn't
people be allowed to write compilers which generate C?