Re: about "Dynamically Linked Functions"

[geraint]

> From: myong <address@hidden>
> Date: Wed 09/Apr/2003 09:03 GMT
> To: octave <address@hidden>
> Subject: about "Dynamically Linked Functions"
> 
> Where can I get more detail information about dynamically linked 
> functions, especially the passing o farguments.
> 


A good starting place is http://octave.sourceforge.net/coda/coda.html. It is 
also highly recommended that you take a look at the examples included in the 
octave source code, such as oregenator.cc.

In answer to the specific question about argument passing, arguments are passed 
to dynamically loaded functions packaged within an octave_value_list, as the 
second argument to the function. The objects then need to be extracted into 
appropriate containers (e.g. column_vector_value) before use. An 
octave_value_list is also returned from the function, so it is possible to 
return more than one object back to Octave.

The following example may serve to illustrate the method.

== myoct.cc ==

#include <octave/oct.h>

DEFUN_DLD (myoct, args, , "dummy function")
{
  octave_value_list retval;
  
  int nargin = args.length();

  if (nargin != 2)
    error("Require 2 input arguments");

  ColumnVector a = args(0).column_vector_value();
  ColumnVector b = args(1).column_vector_value();

  if (a.length() != b.length())
    error("Input vectors not of same length");

  ColumnVector c = a + b;
  ColumnVector d = a - b;

  retval(0) = c;
  retval(1) = d;

  return retval;
}

======
$ mkoctfile myoct.cc
$ octave -q
octave:1> [ c , d ] = myoct ( [ 1 ; 2 ] , [ 3 ; 4 ] )
c =

  4
  6

d =

  -2
  -2

octave:2> 

Hope this helps,
Geraint.

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