Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!uwvax!oddjob!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: What can I get away with
Message-ID: <7270@mimsy.UUCP>
Date: Tue, 30-Jun-87 21:28:20 EDT
Article-I.D.: mimsy.7270
Posted: Tue Jun 30 21:28:20 1987
Date-Received: Thu, 2-Jul-87 00:39:46 EDT
References: <608@zen.UUCP> <2299@hoptoad.uucp> <21211@sun.uucp> <830@omepd> <8190@linus.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 70

In article <8190@linus.UUCP> jfjr@mitre-bedford.ARPA (Jerome Freedman) writes:
>Suppose I declare an array of pointers to functions in one module.
>I write a function, in the same module, which will install functions
>in this array -call the function "install".

>In a different module I write a function, call it "new_function".
>I make NO attempt at making "new_function" visible anywhere outside
>of the module in which it is written.

You have to do something special to make it invisible outside its
own module, namely, declare it `static'.

>I call install on this new_function to put it in my array. ...
>Can I then go through this array of function pointers ... and call
>the functions pointed to even if they are not declared externally
>... ?

Certainly.

	% cat f1.c
	static void (*a[10])();
	static int n_funcs;

	int
	install(f)
		void (*f)();
	{

		if (n_funcs >= sizeof (a) / sizeof (a[0]))
			return (-1);	/* out of space */
		a[n_funcs] = f;
		return (n_funcs++);
	}

	void
	call_all()
	{
		register int i;

		for (i = 0; i < n_funcs; i++)
			(*a[i])();
	}
	% cat f2.c
	/*ARGSUSED*/
	static void
	new_function()
	{

		printf("new_function\n");
	}

	int
	main(argc, argv)
		int argc;
		char **argv;
	{

		(void) install(new_function);
		call_all();
		return (0);
	}
	% cc f1.c f2.c
	% a.out
	new_function
	% 

This assumes your compiler can handle `void (*p[N])()'.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	seismo!mimsy!chris