Re: fortran_vec() vs data() - very first element is lost

[Mike Miller]

On Mon, Oct 24, 2016 at 16:07:18 +0200, Patrick Boettcher wrote:
> Hi list,
> 
> I'm still working in an .oct-file to get in and out complex and
> double matrices.
> 
> I noticed something strange which makes me wonder whether I really got
> it correctly:
> 
> I read here 
> 
>   
> https://www.gnu.org/software/octave/doc/v4.0.1/Matrices-and-Arrays-in-Oct_002dFiles.html
> 
> that I should use the method fortran_vec() to get to the raw-buffer.
> 
> It seems I'm using it correctly to fill data into a matrix returned by
> my oct-function. However, when using this method to access the data of
> a matrix given to my function as an argument the very first element
> contains garbage:

You may have found a bug with this example. I get the same bad result as
you, but other small variations on this theme give the correct values.

Try

  auto matrix = args(0).complex_matrix_value ();
  auto fdata = matrix.fortran_vec ();
  auto data = matrix.data ();

or

  octave_stdout << args(0).complex_matrix_value ().fortran_vec ()[0];

Both of these give me the correct value in the zeroth index.

If you continue to get the wrong value, please report on the bug tracker
(and investigate a little deeper or provide a patch if you can).

> When injecting data into octave I'm using fortran_vec() to get access
> to the raw-buffer. Displaying the matrix in octave shows the first
> element to be correctly set.

Yes, this is the right way to write copy external data into a matrix.

-- 
mike