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From: mikec@ux1.lbl.gov (Mike Chin)
Newsgroups: comp.lang.c
Subject: Set function address into absolute memory?
Keywords: vector table
Message-ID: <2954@helios.ee.lbl.gov>
Date: 7 Jul 89 01:02:02 GMT
Sender: usenet@helios.ee.lbl.gov
Distribution: usa
Organization: Lawrence Berkeley Laboratory, Berkeley
Lines: 46

Is there a reasonable way to place the address of a function into
an absolute location? I need to do this to set up the vector table in
an 80186. I would have thought that something like "a pointer to a function"
set to the table address would work, but it seems I have to wrap it inside
of a structure. Here's an example that shows the structure, and in comments what
seems should be OK. This lints with Gimpel, and runs under MSC 5.1
in large model...
----------------------------------------------------
/*
instead of malloc, for an real vector table I would use
absolute addresses
*/

#include <stdio.h>
#include <malloc.h>

typedef	struct	{
	void (*oopa)();
	}functype;

void	vector();

void main()
{
	void 		(*funcpoint)();
	functype	*funcstruct;
/*
	this won't pass lint
	funcpoint=(void*) malloc (4);
	*funcpoint = vector;
	*funcpoint();
*/

	funcstruct=(functype *) malloc(4);
	funcstruct->oopa=vector;
	funcstruct->oopa();

}

void vector()
{
	printf ("this is the stuff\n");
}
----------------------------------------------------
Mike Chin
MJChin@lbl.gov