Array return argument with typemaps

Hello,

I am wrapping a function that receives a pointer to class, double
parameter and writes the computation to an array:

extern "C" void interp5C(spline *stat, double G, double *f);

The input arguments are working well.  The "stat" object holds the size
of the system and thus the size that "f" should have.

If I do

%typemap(in) spline *stat (int nelems)
{
// stat->n +1 is the size of the problem
  nelems = $1->n + 1;
}

%typemap(in, numinputs=0) double *f (double *temp) {
  temp = new double [nelems];
  $1 = temp;
}

%typemap(argout) double *f {
  dim_vector dv(nelems, 1);
  $result = Matrix(dv);
}

I face the problem that "nelems" is adjusted after it is used in "new
double [nelems]".

I finally created an utility function that outputs the double *:

%inline{
  extern "C" void interp5C(spline *stat, double G, double *f);

  double *interp(spline *stat, double x)
  {
    double *f = new double [stat->n + 1];
    interp5C(stat, x, f);
    return f;
  }
}

with the typemaps

%typemap(out) double * {
  int nelems = arg1->n + 1;
  dim_vector dv(nelems, 1);
  Matrix r(dv);

  for (int i = 0; i < nelems; i++){
    r(i) = $1[i];
  }
  delete [] $1;
  $result = r;
 }

and this works, but I am not entirely convinced with this, because I am
accessing "arg1" directly to refer to "stat", which I think it is not
very clean.

I guess the original problem is similar to wrapping strcpy(), but
slightly modified:

void strcpy( char *dest, const char *src );

where "dest" is to be resized at runtime given the nature of "src".

Is there any way to do it simpler?

Thanks!