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[netCDFJava #YBE-781445]: Redefine mode working for netcdf-java?

I looked at our test cases and see that setRedefineMode is used
in a number of them. So I speculate that your code is doing something
non-standard.

> Directly using the jna is probably a bad idea since other parts of
> netcdf-Java may not see the changes you make.
> 
> A couple of points.
> 1. the netcdf-3 format does not actually have a string type: only character.
> this means that strings are faked as arrays of character, and that means
> that they are fixed size. If you change one without first setting
> redef mode, then any string you pass in will be truncated to fit in the
> existing array of characters.
> 2. I more concerned about the failure of NetcdfWriter.setRedefineMode.
> If you set define mode, then writing a longer string should have worked.
> This needs investigation. By any chance do you have a simple
> java program that illustrates this failure?
> 3. The jna api is missing a number of things we did not anticipate using;
> apparently including redef.
> 4. netcdf-3 files are read and written using pure-java code; the jna is not 
> involved. So, it has internally the functional equivalent of redef. The 
> netcdf-4 library (in C) is more forgiving about doing an automatic redef
> when certain actions are attempted, so explicit redef is not often
> required.
> 
> > I'm writing a java application that updates values of global attributes
> > but have encountered multiple issues while attempting to implement.
> >
> > First I tried using the ucar.nc2.NetcdfWriter but it wasn't capable of
> > updating the attributes to values that exceeded a particular length and
> > ended up truncating the string value.
> >
> > Errors were also thrown when I tried to use the
> > NetcdfWriter.setRedefineMode that was ultimately caused by a Native
> > Windows Filesystem call.  I tested on Linux and a similar error was
> > thrown.
> >
> > Those errors led me to believe that the Netcdf3 writing capabilities
> > weren't working properly for netcdf-java so I attempted to use Netcdf4.
> > I discovered that unlike Netcdf3, netcdf-java doesn't have Netcdf4
> > processing implementation built-in so depends on the Native C Library
> > that must be installed to be accessed via JNA.  After installing the
> > Netcdf4 C Library, the attribute values were still being truncated.
> > After debugging the functions I d iscovered that the Netcdf3 functions
> > were still being used.
> >
> > I didn't find any way to force netcdf files to be processed using netcdf4
> > via the Java API so I decided to attempt just using the underlying JNA
> > native calls (e.g. nc_put_att_text).  I have already successfully tested
> > updating the attribute values using a c program which doesn't truncate
> > the values.  However, I'm unable to do the same thing in Java because
> > the nc_redef function isn't included in the Nc4prototypes class so the
> > attribute values nev er change.
> >
> > Was nc_redef accidentally left out or was the exclusion intentional?
> > Or is there an equivalent of that function that alluded me?
> >
> >
> 
> =Dennis Heimbigner
> Unidata
> 

=Dennis Heimbigner
  Unidata


Ticket Details
===================
Ticket ID: YBE-781445
Department: Support netCDF Java
Priority: Critical
Status: Open
===================
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