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[netCDF #XHT-915046]: Dynamic rank ?

Hi Xxxxx,

> Hello, I'm trying to find the answer to this specific problem : in my
> program I would like to have a "dynamic" number of dimensions for my
> variable "t" because  it depends of 2 _or more_ elements (A, B, C, D,
> ...). Here are few lines working fine in "static" mode :
> 
> int t_id;
> #  define RANK_t 2    // how to make this rank dynamic ?
> int t_dims[RANK_t];
> stat = nc_def_var(ncid, "t", NC_INT, RANK_t, t_dims, &t_id);
> 
> It seems kinda simple, I tried everything but can't make it work, if you
> could help me of point me to some document it would be nice.
> Thanks for your answer,
> Milan
> p.s. I'm programming in C++ but this question is more language-independent.
> ------------------------------------
> netcdf file_name {
> dimensions:
> A = 11 ;
> B = 11 ;
> ...
> variables:
> double A(A) ;
> double B(B) ;
> double ...
> ...
> int t(A, B, ...) ;
> 
> data:
> 
> A = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 ;
> 
> B = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 ;
> 
> ...
> 
> t =
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
> 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100
> ...
> }

Sorry, but there is no way to create a variable with a dynamic rank
in the netCDF API's, if you mean that you want to be able to change
the rank of a variable at run time.  Variables with variaable or
undetermined rank are not part of the netCDF data model.

If you just want to be able to define a netCDF variable with a rank 
that depends on a run-time parameter, that's easy.  For example in
C you would do something like

  int rank_t, t_id;
  int *t_dims;  /* array of dimids to be allocated */

  rank_t = ...;  /* determine what rank you want at run time */
  int *t_dims = malloc(rank_t * sizeof(int));
  for(int i=0; i < rank_t; i++) {
    t_dims[i] = ... ; /* dimid of ith dimension for t */
  }
  stat = nc_def_var(ncid, "t", NC_INT, rank_t, t_dims, &t_id);

In C++ you could allocate the t_dims array with "new".

If you meant something else and I've misunderstood your question,
please let me know.

--Russ

Russ Rew                                         UCAR Unidata Program
address@hidden                      http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: XHT-915046
Department: Support netCDF
Priority: Normal
Status: Closed