help with a DLD function that segfaults after its execution.

[Guillem Borrell Nogueras]

Hi.

I'm writing a wrapper to some ODE routines.  This function tests how a 
function from octave can be called as a C++ function, all into a DLD 
function.

Here's the code

// test_function_call.cpp

#include <octave/oct.h>
#include <iostream>

using namespace std;

const int NDIM=3;
octave_function *input_fcn=0;

void f(double t,double *y,double *yp)
{
  octave_value_list inval;
  octave_value_list outval;
  ColumnVector y_oct(NDIM);
  inval.append(octave_value(t));
  register int i;
  for(i=0;i < NDIM;i++)
    {
      y_oct(i)=y[i];
    }
  inval.append(octave_value(y_oct));
  outval=input_fcn->do_multi_index_op(1,inval);//first argument is nargout
  ColumnVector yp_oct(outval(0).vector_value());
  for(i=0;i < NDIM;i++)
    {
      yp[i]=yp_oct(i);
    }
}


DEFUN_DLD(test_function_call,args, ,
          "testing how to interface functions between octave and C++")
{


  if (args(0).is_function_handle() || args(0).is_inline_function())
    input_fcn=args(0).function_value();
  else
    {
      error("this is not a function handle nor an inline function");
      return octave_value(-1);
    }

  double t=1;
  double y[NDIM];
  double yp[NDIM];
  y[0]=1;
  y[1]=1;
  y[2]=1;
  f(t,y,yp);

  register int j;

  for(j=0;j < NDIM;j++)
    {
      cout << yp[j] << "\n";
    }

  cout << "segfaults" << endl;
}

This function just calls a function of the form:
[yp]=f(t,x) / x in R**3
and returns its result to cout

The function I call is the usual Lorentz attractor:

function xdot=lorentz(t,x)
  a=10;b=28;c=8/3;
  xdot(1,1)=a*(x(2)-x(1));
  xdot(2,1)=x(1)*(b-x(3))-x(2);
  xdot(3,1)=x(1)*x(2)-c*x(3);

Compilation goes fine but the function segfaults at the end of the execution 
and I cant' find the reason.

>> test_function_call(@lorentz) # calls lorentz at [1,1,1]
0
26
-1.66667    <--the result is right
segfaults
panic: Segmentation fault -- stopping myself...

In fact I know the reason: I'm a C++ newbie.

GNU Octave, version 2.1.72 (i686-pc-linux-gnu)
gentoo, compiled with gcc 3.4.6

Thanks

guillem


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