Re: Space, the final frontier...

• To: netcdf-hdf@xxxxxxxxxxxxxxxx
• Subject: Re: Space, the final frontier...
• From: Quincey Koziol <koziol@xxxxxxxxxxxxx>
• Date: Sun, 9 Nov 2003 11:04:13 -0600 (CST)

Hi Ed,

> Here's a snippet of code:
> 
>       /* Create a space for the memory, just big enough to hold the slab
>        we want. Then select it all. */
>       if ((mem_spaceid = H5Screate_simple(var_info.ndims, count, NULL)) < 0) 
>        BAIL(NC_EHDFERR);
>       if (H5Sselect_all(mem_spaceid) < 0)
>        BAIL(NC_EHDFERR);
> 
> Do I need to select the space, or will it automatically be selected
> when created?
    The default selection for dataspaces is the "all" selection, so the
H5Sselect_all() call is not needed.

    Quincey
>From owner-netcdf-hdf@xxxxxxxxxxxxxxxx 10 2003 Nov -0700 11:45:04 
Message-ID: <wrxwua8qczz.fsf@xxxxxxxxxxxxxxxxxxxxxxx>
Date: 10 Nov 2003 11:45:04 -0700
From: Ed Hartnett <ed@xxxxxxxxxxxxxxxx>
To: netcdf-hdf@xxxxxxxxxxxxxxxx
Subject: zero length attrributes...
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Howdy all!

The topic of the day is the perhaps mythical zero length attribute.

Why would one want a zero length attribute? I will leave that question
for the philosophers among us.

Does anyone really use zero-length attributes in the netcdf universe?
Probably there is someone out there who does, since there are a large
number of users out there.

Meanwhile, netcdf supports a zero length attribute, but HDF5,
apparently, does not. When I try to create one I get:

HDF5-DIAG: Error detected in HDF5 library version: 1.6.1 thread 0.  Back trace 
follows.
  #000: H5S.c line 1708 in H5Screate_simple(): zero sized dimension for 
non-unlimited dimension
    major(01): Function arguments
    minor(05): Bad value

Woops! So that doesn't work. My reading of the manual on H5Acreate
informs me that:

 Currently only simple dataspaces are allowed for attribute dataspaces.

So I can't use an extensible attribute.

What do you think, Quincey, is there a way to have a zero length
attribute in HDF5?

Thanks!

Ed