Re: (Fwd) Simple question WRT netCDF

Hi Bill,

Glenn forwarded your netCDF question to me for a reply.  (If you want to be
sure to get an answer even if one or both of us are away from our email,
send your questions to address@hidden.)

>   Can you tell me the data type of the netCDF variable "rh"
> referenced in the example on page 95 of the "NetCDF User's
> Guide", Vers. 2.3, February 1993?
>   I'd like to write an array of structures into a netCDF file
> but don't understand what data type to use for the value argument
> to ncvarputg().

The example opens a previously created netCDF file, so the original NCVDEF
call that defined the RH variable was presumably in a previously run
program.  However from the example it can be inferred that RH was defined as
type NCDOUBLE, corresponding to double precision, since an array of data of
type DOUBLE is being used to overwrite every other value of RH in the example.

In using NCVPTG, you must use data of the type corresponding to the netCDF
variable (DOUBLE for type NCDOUBLE, REAL for type NCFLOAT, INTEGER for type
NCLONG, etc.).  You can find out what the type of the variable is with a
call to NCVINQ.

Neither the compiler nor the library can detect the error if you try to
write the wrong type of data into a netCDF variable (only the C++ interface
permits the detection of such errors).

If by "structures" you mean something like C structs or Pascal records (I
don't remember what the Fortran 90 equivalent is called, modules?), netCDF
doesn't support that abstraction directly, since Fortran 77 had nothing into
which you could read such an object.  So, if you are trying to use NCVPTG to
intersperse writing data of different types in the space allocated for
variable elements of a single type, it won't work.  The C interface has some
interfaces for supporting something like structures (ncrecput, ncrecget,
ncrecinq) but they are really just wrappers around multiple calls, each
reading or writing arrays of data of a single type.

--Russ

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Russ Rew                                                UCAR Unidata Program
address@hidden                                          P.O. Box 3000
http://www.unidata.ucar.edu/                          Boulder, CO 80307-3000
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