Re: [netcdfgroup] need to id netcdf files

• To: parallel-netcdf@xxxxxxxxxxx
• Subject: Re: [netcdfgroup] need to id netcdf files
• From: Wei-keng Liao <wkliao@xxxxxxxxxxxxxxxxxxxx>
• Date: Tue, 2 Feb 2010 13:10:31 -0600

Hi, Jim,

We can add two new functions in pnetcdf library:

int ncmpi_inq_format      (int   ncid,     int *formatp);
int ncmpi_inq_file_format (char *filename, int *formatp);

The return argument "formatp" will be a constant defined in pnetcdf.h.
Currently we have
#define NC_FORMAT_CLASSIC    1
#define NC_FORMAT_64BIT      2
#define NC_FORMAT_64BIT_DATA 5

Since netcdf4 is in HDF5 format, as Russ pointed out, it may not
be as simple to report and return NC_FORMAT_NETCDF4 and
NC_FORMAT_NETCDF4_CLASSIC.

But, we can add
#define NC_FORMAT_UNKNOWN -1
for formats other than the above already-defined three.

Wei-keng

On Feb 2, 2010, at 11:17 AM, Jim Edwards wrote:

Hi Russ,

Maybe I can distill the essence of this function since my goal is to use it before I call the netcdf open function.

I think that 64-bit-offset is the pnetcdf format that I was referring to.

Thanks for the hint about hdf5 files.


- Jim

On Tue, Feb 2, 2010 at 9:58 AM, Russ Rew <russ@xxxxxxxxxxxxxxxx> wrote:

Jim,

> I am in need of a function that can identify a file as netcdf3, netcdf4, or

> pnetcdf 64-bit.

> Preferably I would like this function to work without having linked any of

> the mentioned netcdf libraries.
>
> Does anyone have or know of one?

Although it doesn't match your preference for independence from netCDF
libraries, the nc_inq_format() function documented here:

 
http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-c.html#nc_005finq-Family

distinguishes among the 4 netCDF format variants:

 http://www.unidata.ucar.edu/software/netcdf/docs/faq.html#fv1

in the netCDF-4 library or between classic and 64-bit-offset formats in

a netCDF-3 library.  It doesn't recognize the pnetcdf 64-bit variant.

By the way, an HDF5 file can't necessarily be distinguished by its first

4 bytes, because HDF5 files may begin with a "user-block" of size 512,
1024, 2048, ... bytes, before the 4-byte file-type signature.

--Russ

• References:
  • [netcdfgroup] need to id netcdf files
    • From: Jim Edwards
  • Re: [netcdfgroup] need to id netcdf files
    • From: Russ Rew
  • Re: [netcdfgroup] need to id netcdf files
    • From: Jim Edwards