Path: utzoo!attcan!uunet!clyde.concordia.ca!news-server.csri.toronto.edu!turing.toronto.edu!tarvydas
From: tarvydas@turing.toronto.edu (Paul Tarvydas)
Newsgroups: comp.lang.eiffel
Subject: Re: eiffel and external c routines
Message-ID: <1990Oct18.105958.2492@jarvis.csri.toronto.edu>
Date: 18 Oct 90 14:59:58 GMT
References: <444@kepler1.kepler.com>
Organization: CSRI, University of Toronto
Lines: 93

There's a problem with your C code and with documentation:

	1) My copy of 'Eiffel: The Language' incorrectly documents
	   "eif_rout".  It returns a *pointer* to a routine.  [Also,
	   the names in the C string must be entirely lower case and
	   25 characters or less.] So, after calling "eif_rout", you
	   still have to call the routine, eg. 

	   	(*(eif_rout (obj, "feat"))) (obj);

	   or, more humanely put (and, more efficiently, if you're going
	   to make the call more than once):

	   	ptr = eif_rout (obj, "feat");
		...
		(*ptr) (obj);

	   [Remember that you have to supply the "Current" Eiffel object
	   as the first arg to an Eiffel routine.]

	 2) Your C code is wrong because "item" is a routine, not an
	    attribute (maybe that's why you got the -1 eif_err's).

So, here's your C code:
============================
#include <stdio.h>
#include "/home/Eiffel/files/_eiffel.h"
foo(x)
OBJPTR x;
{
  
  int i;
  extern int eif_err;
  extern ROUT_PTR eif_rout ();
  ROUT_PTR item, forth;

  item = eif_rout (x, "item");
  if (item == NULL) {
    fprintf (stderr, "can't find 'item'\n");
    exit (1);
  }

  forth = eif_rout (x, "forth");
  if (item == NULL) {
    fprintf (stderr, "can't find 'forth'\n");
    exit (1);
  }

  for (i = 1; i <= 3; i++) {
    printf("i = %d (%d) {%d} [%d]\n",
	   i, eif_err,
	   eif_attr (x, "count"),
	   (*item) (x));
    (*forth) (x);
  }
}
==============================

And here's the output:

1
2
3
i = 1 (0) {3} [1]
i = 2 (0) {3} [2]
i = 3 (0) {3} [3]


As to your question about C-creating instances of generic types, why not
write a new class, say "fixed_list_of_integer", then Create it? eg.

	class
	  FIXED_LIST_OF_INTGER
	export
	  repeat FIXED_LIST
	inherit
	  FIXED_LIST [INTEGER]
	    rename
	      Create as flCreate
	feature
	  Create (n : INTEGER) is
	    do
	      flCreate (n);
	    end;
	end;

Paul Tarvydas
tarvydas@tsctrl.uucp
TS Controls
5 Bowness Crt.
Etobicoke, Ontario, Canada
M9B 5Z8
tel. (416)-234-0889, fax. (416)-234-9193