From help-octave-request at bevo dot che dot wisc dot edu  Fri Jan 19 10:12:10 2001
Subject: Re: .oct-files/ library-wrapper
From: Ben Sapp <bsapp at lanl dot gov>
To: Daniel Heiserer <Daniel dot Heiserer at bmw dot de>
CC: "help-octave at bevo dot che dot wisc dot edu" <help-octave@bevo.che.wisc.edu>
Date: Fri, 19 Jan 2001 09:12:12 -0700

Daniel Heiserer wrote:
> 
> Hi,
.
.
.
> How do I know what kind of datatype is args(j)?

in octave/src/ov.h   There are a number of functions defined to
determine the data type.  They are:

is_cell();
is_real_scalar();
is_real_matrix();
is_complex_scalar();
is_complex_matrix();
is_char_matrix();
is_string();
is_range();
is_map();
is_stream();
is_list();
is_magic_colon();
is_all_va_args();
is_bool_type();
is_real_type();
is_complex_type();
is_scalar_type();
is_matrix_type();
is_numeric_type();

Then once you determine the correct type you can get it representation
with something like:

ComplexRowVector = args(0).complex_row_vector_value();

If the data type is a new data type the above "is_" function won't be of
much use.   Then you will have to use a technique similar to what is
used in examples/make_int.cc(Look at the "doit" dynamically linked
function.) 

> How do I define multiple output arguments is it the same
> by just creating a list?
> retval(1) = a;
> retval(0) = b;

I don't think that will work.   Below is a small example that will work.
You use the third arguement to your DLD function to find out how many
arguements are asked for on the command line.   Then you add elements to
the list by using the append and prepend member functions.  

mlist source:
-----------------------------------------------
#include <octave/config.h>
#include <string>

#include <octave/error.h>
#include <octave/input.h>
#include <octave/pager.h>
#include <octave/oct-obj.h>
#include <octave/utils.h>
#include <octave/gripes.h>
#include <octave/ov.h>
#include <octave/ov-usr-fcn.h>
#include <octave/ov-fcn.h>
#include <octave/pt-pr-code.h>
#include <octave/pt-stmt.h>
#include <octave/toplev.h>
#include <octave/unwind-prot.h>
#include <octave/variables.h>
#include <octave/defun-dld.h>
#include <octave/defun-int.h>

DEFUN_DLD(mlist,args,nargout,
"return a variable number of arguments.")
{
  octave_value_list retval;
  
  for (int i = 0;i < nargout;i++)
    {
      retval.append(octave_value(double(i+1)));
    }
   
  return retval;
}
--------------------------------------------------

On my machine some sample output looks like so:
octave:2> a = mlist
a = 1
octave:3> [a,b] = mlist
a = 1
b = 2
octave:4> [a,b,c] = mlist
a = 1
b = 2
c = 3
octave:5> [a,b,c,d] = mlist
a = 1
b = 2
c = 3
d = 4

Lastly, as far as a library wrapper, I do not know of any.  

Good luck.  

-- 
Ben Sapp                         Los Alamos National Laboratory
email: <mailto:bsapp at lanl dot gov>   Phone: (505)667-3277
Fax:   (505)665-7920             URL:   http://www.neutrino.lanl.gov/
--



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