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Path: utzoo!mnetor!seismo!vrdxhq!bms-at!stuart
From: stuart@bms-at.UUCP (Stuart D. Gathman)
Newsgroups: comp.lang.c
Subject: Re: Function prototypes versus open()
Message-ID: <409@bms-at.UUCP>
Date: Mon, 29-Jun-87 18:39:07 EDT
Article-I.D.: bms-at.409
Posted: Mon Jun 29 18:39:07 1987
Date-Received: Wed, 1-Jul-87 01:55:23 EDT
References: <18346@ucbvax.BERKELEY.EDU> <8042@utzoo.UUCP> <2210@hoptoad.uucp> <817@mcgill-vision.UUCP>
Organization: Business Management Systems, Inc., Fairfax, VA
Lines: 56
Summary: How about this:

In article <817@mcgill-vision.UUCP>, mouse@mcgill-vision.UUCP (der Mouse) writes:
> In article <20538@sun.uucp>, guy%gorodish@Sun.COM (Guy Harris) writes:

> > Trivial.  Have the argument to the dispatcher, instead of being a
> > pointer to a function with a variable number of arguments, be a union
		. . .

> Consider the call to the dispatcher that would have been written (under
> the old K&R paradigm) as

> int fxn();
> ...
> dispatcher(....,fxn);

> How does on write the corresponding thing?  (Please forgive any syntax

> int fxn(int x; int y; double z);
> ...
> dispatcher(....,fxn);

*** Solution A

typedef union {
  int (*type3)(int,int,double);
  int (*type4)(int,int,double,double);
} disp_fxn;
...
dispatcher(....,(disp_fxn)fxn);

I know, this is not allowed, but I wish it was!  Perhaps it should be:

dispatcher(....,((disp_fxn)fxn).type3);
	or
dispatcher(....,(disp_fxn.type3)fxn);

Would this be portable?  Uglier, but I know it would work is:

*** Solution B

{ disp_fxn temp; dispatcher(....,temp.type3=fxn); }

We use indirect functions all over the  place.  We  not  been  using
function  prototypes since some of the compilers we support don't
have them.  As a result, there are many bugs resulting  from  the
wrong  parm  type  being  passed  to  a function called through a
table.  It would be nice to have a way to lint indirect  function
calls without the mess of 'B'.

Worse yet, are dynamic indirect function calls.  This is where the
function pointers are themselves stored in a table!  This is impossible
to lint, since lint cannot guarrantee what kind of pointer will actually
reside in a function pointer variable at run time.  At this point, I
start leaning towards O-O!
-- 
Stuart D. Gathman	<stuart@bms-at.uucp>
			<..!seismo!dgis!bms-at!stuart>