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From: duns1222@w203zrz.zrz.tu-berlin.de (Martin Dunschen)
Newsgroups: comp.lang.eiffel
Subject: passing address of an eiffel feature
Keywords: fortran, eiffel-c, address passing, complex feature
Message-ID: <280@mailgzrz.tu-berlin.de>
Date: 5 Mar 91 16:34:44 GMT
Sender: news@mailgzrz.tu-berlin.de
Organization: TUBerlin
Lines: 169
Nntp-Posting-Host: w203zrz.zrz.tu-berlin.de

Hello everybody,

I have a problem passing the address of an Eiffel feature
to a foreign routine, written in C.

In the case you want to pass the address of a simple feature,
like a real, it seems to be no problem. Also, as given in the
example $EIFFEL/examples/.../callbacks, comming along with version 2.3,
it is possible to pass pointers to eiffel-routines.

But how to pass pointers to complex features, like ARRAY[REAL] ?

The reason, we want to do this, is the reuse of software, written
in FORTRAN77. If you know this language, you can imagine that there
is extensive use of fortran arrays, passed via parameterlists.

Because Eiffel 2.3 does not know external clauses with 
language "Fortran", we use short C procedures, which call the 
Fortran subroutines. The argument passing and all other problems
using C together with Fortran are already solved.

To supply the Fortran subroutine with these arrays, or getting back
the results of a computation on an array, we think about using
the possibility of passing pointers of Eiffel features to foreign
routines, this is descibed very brief in 
"Eiffel: The language (version 2.2)", pages 218, 219.

Perhaps there is a workaround?

Nevertheless I include a few C routines and eiffel-classes,
showing in two examples what I mean.

You cut this file at the indicating lines, put the parts in new
files, named .eiffel, test.e, c_test.c for example 1 in one directory,
and the others, with same names in another directory. Compile the
C-routine in each directory and invoke es. The executable in example
1 does what I expect, example 2 is somehow a clue for me!

Thanks in advance, Martin

+-----------------------------------------------------------------+
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+-----------------------------------------------------------------+
CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------
--
-- Beginning of first example, following files are .eiffel, test.e, c_test.c
--
------------ EIFFEL SYSTEM DESCRIPTION FILE -------------------
--   For simple uses, just replace ``root_class_name'' below
--   by the name of the root class of your system (lower case)
ROOT: test
UNIVERSE: $EIFFEL/library/structures $EIFFEL/library/support
EXTERNAL: c_test.o
NO_ASSERTION_CHECK (N): ALL
PRECONDITIONS (Y): ALL
ALL_ASSERTIONS (N): ALL
DEBUG (N):
TRACE (N):
OPTIMIZE (N): ALL
GARBAGE_COLLECTION (N)
C_PACKAGE (N):
C_EXTERNAL:
MAKE:
VISIBLE (N):
CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------
--|
--| test.e
--|
class TEST

feature

        value : REAL;

	Create is
            external c_test language "C"
        do
              value := 25.;

              io.putstring (" this is test.e value=");
              io.putreal (value);
              io.putstring ("\n");

              c_test (@value);

              io.putstring (" this is test.e, after c_test value=");
              io.putreal (value);
              io.putstring ("\n");

        end --create

end -- class TEST
CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------
/* c_test.c */
c_test (parm)
float *parm;
{
	printf ("this is c_test, parm= %f \n", *parm);
        *parm = *parm +25.;
}
CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------
--
-- Beginning of second example, following files are .eiffel, test.e, c_test.c
--
------------ EIFFEL SYSTEM DESCRIPTION FILE -------------------
--   For simple uses, just replace ``root_class_name'' below
--   by the name of the root class of your system (lower case)
ROOT: test
UNIVERSE: $EIFFEL/library/structures $EIFFEL/library/support
EXTERNAL: c_test.o
NO_ASSERTION_CHECK (N): ALL
PRECONDITIONS (Y): ALL
ALL_ASSERTIONS (N): ALL
DEBUG (N):
TRACE (N):
OPTIMIZE (N): ALL
GARBAGE_COLLECTION (N)
C_PACKAGE (N):
C_EXTERNAL:
MAKE:
VISIBLE (N):
CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------
class TEST

feature

        list : ARRAY[REAL];

	Create is
            external c_test language "C"
        do
              list.create(0,2);
              list.put (  10.,0);
              list.put (  20.,1);
              list.put (  30.,2);

              io.putstring ("test, before c_test:\n");
              io.putreal (list.item (0));
              io.putstring ("\n");
              io.putreal (list.item (1));
              io.putstring ("\n");
              io.putreal (list.item (2));
              io.putstring ("\n");

              c_test (@list);

              io.putstring ("test, after c_test:\n");
              io.putreal (list.item (0));
              io.putstring ("\n");
              io.putreal (list.item (1));
              io.putstring ("\n");
              io.putreal (list.item (2));
              io.putstring ("\n");
        end --create

end -- class TEST
CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------CUT HERE ------
c_test (list)
float *list;
{
	printf ("this is c_test, list(0)= %f \n", list[0]);
	printf ("                list(1)= %f \n", list[1]);
	printf ("                list(2)= %f \n", list[2]);
        list[0] = list [1] + list [2];
}