From octave-maintainers-request at bevo dot che dot wisc dot edu Thu Nov 20 22:57:23 2003
Subject: accessing user-defined types from C++
From: pkienzle at users dot sourceforge dot net
To: octave-maintainers mailing list <octave-maintainers at bevo dot che dot wisc dot edu>
Date: Fri, 21 Nov 2003 00:00:19 -0000

While we are on the topic of the type system, I've been
playing with methods for accessing sparse types from
functions outside sparse.oct.  

Curiously enough,  if I define the two oct-files:

hello.cc:
======

#include <octave/oct.h>

void world(void)
{
  octave_stdout << "world" << std::endl;
}

DEFUN_DLD(hello,args,nargout,"hello")
{
   octave_stdout << "hello" << std::endl;
   return octave_value_list();
}


world.cc:
=======
#include <octave/oct.h>

DEFUN_DLD(world,args,nargout,"world")
{
  void world(void);
  world();
  return octave_value_list();
}

everything works as expected:

octave:1> hello
hello
octave:2> world
world

Things won't be quite so easy on windows methinks 
because I will need to link world.oct directly against 
hello.oct.  I haven't tried that yet, but it will certainly
complicate the build system for octave-forge.

Anyone have a better how I can write an independent DLD 
function which accesses data from the sparse type?  
Right now the built-in types occupy a privileged place 
by virtue of having methods in the octave_value base 
class to access them.

BTW, octave 2.1.51 fails on Linux if I do things in the
other order, crashing octave in the process:

octave:1> world
octave: relocation error: 
/home/pkienzle/prog/octave/crosslink/world.oct: undefined symbol: 
_Z5worldv
[crosslink]#

Paul Kienzle
pkienzle at users dot sf dot net