Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!husc6!mit-eddie!genrad!decvax!decwrl!pyramid!prls!philabs!micomvax!musocs!mcgill-vision!mouse
From: mouse@mcgill-vision.UUCP (der Mouse)
Newsgroups: comp.lang.c
Subject: Re: Function prototypes versus open()
Message-ID: <817@mcgill-vision.UUCP>
Date: Mon, 22-Jun-87 22:46:11 EDT
Article-I.D.: mcgill-v.817
Posted: Mon Jun 22 22:46:11 1987
Date-Received: Sat, 27-Jun-87 04:47:36 EDT
References: <18346@ucbvax.BERKELEY.EDU> <8042@utzoo.UUCP> <2210@hoptoad.uucp> <20538@sun.uucp>
Organization: McGill University, Montreal
Lines: 37

In article <20538@sun.uucp>, guy%gorodish@Sun.COM (Guy Harris) writes:
>> Wait a sec. Would you please explain how the following can be done:

>> [dispatcher which calls a fxn passed by a pointer as an argument,
>>  with 3, 4, or 5 args.  Each fxn expects known arg pattern.]

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

Except that this makes it effectively impossible to use the dispatcher.
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
errors, I don't have a copy of the draft - and won't until I can get
one machine-readable!)

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

Oops.  The argument to the dispatcher is not of type
int (*)(int,int,double)
but of type
union{int(*)(int,int,double);int(*)(int,int,double,double);}
instead.  Ugly.

					der Mouse

				(mouse@mcgill-vision.uucp)