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Re: 20031118: netcdf data problem (fwd)

Hi Birgit,

>To: <address@hidden>
>From: "Birgit Heese" <address@hidden>
>Subject: netcdf data problem
>Organization: MIM
>Keywords: 200311171529.hAHFT5Ob010057

In the above email, you wrote:

> I have a problem in replacing some variables in a netcdf-file. I am
> getting some additional zeros at the end of the data. I am just
> opening the file and cheching the variable id and then putting a new
> value for this variable. I am not manipulating the data itselv at
> all. Nevertheless, the program is adding zeros behind the data.

Thanks, you have identified a bug.  I now have very simple C program
that demonstrates the bug by changing the value of the only variable
in a one-variable 72-byte netCDF file; the file grows to 4096 bytes
when it is closed.  Apparently the size of the file is getting rounded
up to the nearest multiple of 4096 with extra zero bytes, although
this does not happen for files created, written, and closed without
being rewritten.  

Using only the netCDF interface, it is not detectable whether a file
has any number of extra zero bytes appended to it.  It would be
possible to shrink all your files, getting rid of the extra zero
bytes, by a program that truncated them with the ftrunc() call if you
knew how long they were supposed to be, but that would not be a good
long term solution :-).

Now that we can reproduce the problem with a simple test case, we'll
try to determine where the bug is and provide a fix.  Thanks for
reporting the problem!

--Russ

_____________________________________________________________________

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