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[netCDF #HQN-423106]: netcdf4 with NC_NETCDF4 and NC_64BIT_OFFSET

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  • Subject: [netCDF #HQN-423106]: netcdf4 with NC_NETCDF4 and NC_64BIT_OFFSET
  • Date: Thu, 01 Sep 2011 12:47:51 -0600
Hi Greg,

> I tried to create a netcdf file using NC_NETCDF4 & NC_64BIT_OFFSET &
> NC_CLASSIC_MODEL and it fails.  Looking at nc4file.c, there is an
> explicit check that disallows for both NC_NETCDF4 and NC_64BIT_OFFSET
> both being set.
> 
> Is this intentional (or, obviously this is intentional, what is
> the background on this decision).   I have a model that needs to use
> NC_NETCDF4 and the NC_CLASSIC_MODEL, but has a dimension that exceeds 2^31
> (but is < 2^32).

Yes, it's intentional.  NC_64BIT_OFFSET is only intended to specify use of 
the variant of the classic format that uses 64-bit offsets instead of 32-bit 
offsets.  It corresponds to format 2 of the four netCDF format variants.  All 
netCDF-4/HDF5 files (formats 3 and 4) uses 64-bit offsets as far as I know.

If you use (NC_NETCDF4 || NC_CLASSIC_MODEL) that will use netCDF-4/HDF5
storage with 64-bit offsets.  The "NC_CLASSIC_MODEL" refers to the data model, 
not the format.

This should be documented more clearly to avoid the confusion you point out.

> If I remove the check, what break?

I don't know, but I would recommend not removing the test, instead just removing
use of NC_64BIT_OFFSET from the nc_create() call.

--Russ

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



Ticket Details
===================
Ticket ID: HQN-423106
Department: Support netCDF
Priority: Normal
Status: Closed