[netcdfgroup] On deflate argument of nc_def_var_deflate

• To: netcdfgroup@xxxxxxxxxxxxxxxx
• Subject: [netcdfgroup] On deflate argument of nc_def_var_deflate
• From: Shin-ya Murakami <murashin@xxxxxxxxxxxxxx>
• Date: Tue, 01 Sep 2015 17:30:10 +0900 (JST)

Hi,

I found unexpected behavior for me on deflate argument of
nc_def_var_deflate in NetCDF 4.3.3.1.

The NetCDF C Interface Guide 
(https://www.unidata.ucar.edu/software/netcdf/docs/netcdf-c/nc_005fdef_005fvar_005fdeflate.html)
says that 'deflate' argument is
'If non-zero, turn on the deflate filter at the level specified by
the deflate_level parameter. '

I expected that turn off the deflate filter
if deflate argument is zero with non-zero deflate_level value.

The current behavior is that, deflate filter turns on
with deflate=0 and deflate_level=1(non-zero).

nc_def_var_extra function in libsrc4/nc4var.c

  849:   /* Check compression options. */
  850:   if (deflate && !deflate_level)
  851:      return NC_EINVAL;

should be modified like following:

  849:   /* Check compression options. */
  850:   if (!deflate || !deflate_level)
  851:      return NC_EINVAL;

or the guide should be corrected.

Thank you,
----
Shin-ya Murakami
  Institute of Space and Astronautical Science,
  Japan Aerospace Exploration Agency.
email: murashin@xxxxxxxxxxxxxx