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[netCDF #GPR-287619]: netcdf_c++ bug in 4.1.3?


> On Tue, 27 Dec 2011, Unidata netCDF Support wrote:
> > The C++ library version in 4.1.3, from the cxx directory, was intended for
> > netCDF classic format files. Are you actually using the experimental cxx4
> > library from the cxx4 directory?
> The library was built (not by me!) using the --enable-netcdf-4 flag to
> configure. The installation note toward the bottom of
> http://www.unidata.ucar.edu/software/netcdf/docs/cxx4/
> is a bit cryptic, as the text says it is necessary to use the
> --enable-netcdf-4 flag in configuring but the following example uses
> --enable-cxx-4. Are these equivalent?

No, --enable-netcdf-4 builds libraries that understand additional formats
and have additional functions in the C or Fortran API, enabled by using
the HDF5 library as a storage layer to support an enhanced data model.
You may find this FAQ answer clarifies the relationships among the data
formats, models, and APIs:


The --enable-cxx-4 flag requires the enable-netcdf-4 flag, but specifies
that a new version of the old C++ API should be built and tested.  This
new version supports most of the the netCDF-4 enhanced data model and formats.
It is not designed to be backward compatible with the C++ interface, which
was designed before exceptions and templates were even in the C++ standard.

> > So I assume "ncdump -k power_test1.nc" outputs "netCDF-4" for the file 
> > format.
> That's correct.
> > The "1L" type for the bolos:matrix attribute indicates an attribute of
> > type int64 rather than int.  NetCDF-4 files can use 6 primitive types that
> > are not in the netCDF classic data model, including NC_INT64 which has the
> > value 10.
> That's what I assumed it should be from ncdump (I didn't modify the
> netcdf.cpp file, either; this problem just got kind of dumped in my lap).
> I tried replacing it with as_double() - should that have worked?

I don't know, as I'm not familiar with the new cxx4 API yet.

> > From your use of the as_int() method, it looks like you're trying to use the
> > old C++ code for classic format files on a new netCDF-4 format file which is
> > making use of extended types in the netCDF-4 data model.  I'm surprised that
> > the old cxx API can even open a netCDF-4 file; it should just return an
> > unrecognized file type of error when that is attempted.
> > The C++ API we have for netCDF-4 files is in the cxx4 directory and is only
> > built if you use the --enable-cxx-4 flag to configure.  There's a 
> > stand-alone
> > version of the netCDF-4 C++ libraries, separated out from the C software, as
> > announced here:
> >
> >  
> > http://www.unidata.ucar.edu/mailing_lists/archives/netcdfgroup/2011/msg00365.html
> >
> > and documented here:
> >
> >  http://www.unidata.ucar.edu/software/netcdf/docs/cxx4/
> What's the difference (if any) between the --enable-cxx-4 and
> --enable-netcdf-4 flags?

I hope that's clear from the explanation above.


> > Ticket Details
> > ===================
> > Ticket ID: GPR-287619
> > Department: Support netCDF
> > Priority: Normal
> > Status: Closed
> >

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

Ticket Details
Ticket ID: GPR-287619
Department: Support netCDF
Priority: Normal
Status: Closed

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