Re: gsl_vector_const_view: pointer to constant or constant pointer

[Brian Gough <bjg at network-theory dot co dot uk>]

Fleur Kelpin writes:
 > Is it correct that the definition
 > typedef struct
 > {
 >   const gsl_vector *vector;
 > } gsl_vector_const_view;
 > would have the advantage that gsl_vector_const_view s can be initialized
 > and reassigned but the disadvantage that memory is allocated for the
 > vectors in the views and will need to be freed after use?

Views are intended to be lightweight objects -- this is the main
reason they are allocated on the stack, to avoid the overhead of
calling malloc.  It also means that they don't have to be freed.

 > I ended up changing to non-const gsl_vector_view and casting the const
 > from my arrays, as Joohnas Pihlaja suggested. The other solution I could
 > think of was sticking to const double * s and creating the
 > gsl_vector_const_view only last minute when I need it.

The latter is definitely preferred.  Views should always be
initialised at the same time they are defined, opening up a new scope
if needed.  It should not be necessary to cast away const when using
GSL.

e.g.

int main()
{
  const double x[]={1,2,3,4};
  ...
 
   {
      gsl_vector_const_view xview = gsl_vector_const_view_array(x,4);
      ....
    }
  return 0;
}