Re: Include Fortran Code which Returns Arrays of Dynamic/Unknown Size

[Marco2008]

John W. Eaton wrote:
> 
> I don't know how to call this function from C/C++.
> 
> If you had a similar function in C++, for example something like
> 
>   void foo (double **v, int *len)
>   {
>     len = 10; // or some computed value
>     *v = new double [len];
> 
>     // fill V here ...
>   }
> 
> then you could call it from an Octave DEFUN like this:
> 
>   double *v;
>   int len;
>   foo (&v, &len);
> 
> and then copy the values from V to an appropriately sized Matrix
> object:
> 
>   Matrix m (len, 1);
>   double *pm = m.fortran_vec ();
>   for (int i = 0; i < len; i++)
>     m[i] = v[i];
> 
> then you would probably also want to free the memory allocated in FOO
> to avoid a memory leak:
> 
>   delete [] v;
> 
> Is an allocatable array in Fortran some kind of object that carries
> with it the size?  If so, then I think you need to know precisely what
> your compiler does so that you can call a function like this from C++
> (probably the details are implementation defined, so will not be
> portable).  Or is it guaranteed to just be a pointer to some data?  If
> it is just a pointer, then I think you will need to modify your
> function so that it also returns the size.  Otherwise, how can a C++
> function that calls your Fortran function know how large the allocated
> array is?
> 
> jwe
> _______________________________________________
> Help-octave mailing list
> address@hidden
> https://www-old.cae.wisc.edu/mailman/listinfo/help-octave
> 

Hello!
Thanks for this idea.
I tried a bit with this approach. It brought me to the following code:

subroutine funfortrantwo(size1, vector1)
        implicit none
        integer :: size1
        real(8) :: vector1(size1)
        vector1 = 2
        ! write(6,*) vector1
end subroutine funfortrantwo

#include <octave/oct.h>
#include <iostream>
#include "f77-fcn.h"
extern "C"
{
        F77_RET_T
        F77_FUNC (funfortrantwo, FUNFORTRANTWO) (int& n1, double* m1);
}
DEFUN_DLD (fun_cpp2, args, ,"...")
{
    octave_value_list retval;
        double* m1;  
        int n1 = 7;
        F77_XFCN (funfortrantwo, FUNFORTRANTWO,
                        ( n1, m1 ) );
        if (f77_exception_encountered)
        {
                error ("Error!");
                return retval;
        }
        int i1 = n1;
        Matrix M1 (i1,1);
        for (int i = 0; i < i1; i++)
        {
                double h1 = m1[i];
                M1.fill(h1,i,0,i,0);
        }
        retval(0) = M1;
        return retval;
}

it can be compiled by mkoctfile. But inside octave I get:

panic: Segmentation fault -- stopping myself...
attempting to save variables to `octave-core'...
save to `octave-core' complete
Segmentation fault

If I replace int  
    int i1 = n1;
by 
   int i1 = 7;
it works correctly for one time. The second time fails with the above
mentioned panic. Maybe the  memory management in my c++-file is not correct.


-- 
View this message in context: 
http://www.nabble.com/Include-Fortran-Code-which-Returns-Arrays-of-Dynamic-Unknown-Size-tp19845758p19925697.html
Sent from the Octave - General mailing list archive at Nabble.com.