Xref: utzoo comp.lang.c:23689 comp.unix.wizards:19285
Path: utzoo!censor!geac!jtsv16!uunet!wuarchive!udel!haven!mimsy!chris
From: chris@mimsy.umd.edu (Chris Torek)
Newsgroups: comp.lang.c,comp.unix.wizards
Subject: Re: (* func)(fred, bert)
Message-ID: <20668@mimsy.umd.edu>
Date: 10 Nov 89 03:24:51 GMT
References: <2387@stl.stc.co.uk>
Followup-To: comp.lang.c
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 58

In article <2387@stl.stc.co.uk> dsr@stl.stc.co.uk (David Riches) writes:
>I want a function with the following interface, that does some actions
>when a signal activates it :-

I had a hard time figuring out what you meant to happen, since your
example is not anything like legal C.  (Refer to <2387@stl.stc.co.uk>
to see the original code.)  I think, though, that what you want is
to call a function (`error') on a signal such as SIG_ALRM.  This much
you can do directly in (proposed) standard C.  However, you want that
function to be passed two arguments that can be specified at the
call to signal().  This you cannot do directly.  You will have to
use a global variable (horrors! :-) ).

According to the pANS, a signal function is called with the signal
number, and nothing else.  Hence, something like this will be
required.

	struct info_needed_during_signal_handler {
		void (*fn)(int, int *);
		int code;
		int *status;
	} siginfo;

	void signal_catch_function(int sig) {
		(void) signal(SIG_ALRM, signal_catch_function);
		(*siginfo.fn)(siginfo.code, siginfo.status);
	}

	void set_catch(void (*fn)(int, int *), int code, int *status) {
		siginfo.code = code;
		siginfo.status = status;
		siginfo.fn = fn;
		(void) signal(SIG_ALRM, signal_catch_function);
	}

Then, instead of:


>[mysterious version of error() deleted]
>
>VOID main()
> {
>  signal(SIG_ALARM, error(101, &stat);		<----------------- (B)
	...

you would write

	void error(int code, int *status) {
		*status = Fn(code);
	}

	int main() {		/* main returns an int, if it returns! */
		set_catch(error, 101, &stat);
			...
	}
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@cs.umd.edu	Path:	uunet!mimsy!chris