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Re: Renaming netCDF item with longer name

> Date: Thu, 13 May 1999 11:17:38 -0400
> To: Russ Rew <address@hidden>
> From: address@hidden (Chuck Denham)
> Subject: Renaming netCDF item with longer name

Hi Chuck,

>         We make big netCDF files of oceanographic data.  Depending on our
> customer, we sometimes have to rename our variables using longer names.  To
> avoid automatically rewriting the netCDF file in such cases, I want to
> provide some name padding right up front.  However, when I do "vardef" with
> a long fake name, and then rename it immediately with the correct shorter
> name, the file doesn't seem to preserve any of the padding I intended.  Do
> I need to go through an "endef/redef" cycle to make the padding stick?  Do
> you know of a reliable strategy?

I think before renaming with a short name, you need to make sure
nc_enddef or nc_close gets called, which actually computes the
space needed on the disk and commits it.  Then nc_rename_var with
the short name(s), and nc_close will store the variable with
padding.

I just verified that you can then call nc_open, nc_rename_var to a
longer name, and nc_close, without calling nc_redef or nc_enddef, to
rename to a longer name.  I was surprised by this, since I thought
nc_redef/nc_enddef was necessary in this case to extend the name, but
it's not.

There is also another way, though it's currently only documented in
the netcdf man page reference documentation, and not the User's
Guides.  That's to use the "underbar underbar" function nc__enddef
after the nc_create (or nc__create) to set the tuning parameter
h_minfree on the dataset, which reserves extra space in the header for
subsequent expansion.  (By the way, the man page documentation in the
netCDF 3.4 release misspells this function as "nc__endef", but I've
just fixed it for the upcoming netCDF 3.5 release to be "nc__enddef").
I haven't tested this, but that's what the h_minfree parameter is
intended for, as well as adding new dimensions, variables, and
attributes later without copying data.

--Russ

_____________________________________________________________________

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