[Solved differently] Re: Hpw to assign a struct to a cell array element in an .oct file

[Philip Nienhuis]

Hi Endre:

Kozma, Endre wrote:
> On Sat, 2015-12-19 at 07:55 -0800, PhilipNienhuis wrote:
>
> > The setup of  the (AFAIU) relevant statements goes as follows:
> >
> > :
> > int band_count = poDS->GetRasterCount();    // call a GDAL library function
> > :
> > Cell m_band(band_count);         // declare m_band to be a cell array
> > :
> > for (int curr_band = 0; curr_band < band_count; curr_band++) {
> > :
> > < generate struct with raster info for current band >
> > < finally resulting in a struct (octave_scalar_map) band_struct >
> > :
> > m_band(curr_band) = band_struct;   // crash if curr_band > 0
> > :
> I'm afraid something went wrong with the generation of band_struct.
> Could you not post this part of code?
> I suggest replacing the struct generation temporarily with something
> very simple thing like this
>
> octave_scalar_map band_struct;
> band_struct.assign("answer", 42);
>
> and checking whether it crashes. I use a very similar code-structure as
> you do, except I assign my structs to an octave_value_list.
> Note, there is a more appropriate type for index variables:
> octave_idx_type.

Thanks.

No, filling band_struct works perfectly for 1-band raster data so that 
part works. It is the assignment to a cell array that is flawed in the 
function.

In the mean time I sought an alternative solution; rather than returning 
a cell array of structs, I preferred a struct array anyway. The original 
author didn't want that but as package maintainer I have some degrees of 
freedom :-)

So I scoured octave's sources for an example and found __magic_read__.cc
Copying some constructs from it the function "gdalread.cc" can now read 
multi-band raster data fine.

Indeed the index should be "octave_idx_type"; I had already tried that 
but that didn't help with cell arrays. For the struct arrays it seems to 
be required (they won't get "filled" otherwise).

So now I have the following code:

:
static const char *fields[] = {"bbox", "data", "min", "max", "ndv"};
octave_map m_band (dim_vector (band_count, 1), string_vector (fields)); 
  /// line wrap
octave_idx_type curr_band;
octave_scalar_map band_struct = (string_vector (fields));
:
for (octave_idx_type curr_band = 0; curr_band < band_count; curr_band++)
 {
  :
  < fill up band_struct with raster data>
  :
  m_band.fast_elem_insert (curr_band, band_struct);
}


Philip