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Re: writing/reading scalars

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  • Subject: Re: writing/reading scalars
  • Date: Wed, 30 Nov 1994 09:08:06 -0700
Oops, forgot to CC: support-netcdf on this when I sent it ...

> From: address@hidden (Charlie Zender)
> Organization: NCAR / CGD
> Keywords: 199411300111.AA07035

Hi Charlie,

> i'm unclear how one should treat scalar variables with netcdf.
> by scalar variable i simply mean a single number.
> my method is to define them as variables with 0 dimensions,
> write them out with ncvarput1, and read them in with ncvarget1
> with the mindex argument set to 1. this method seems to work
> in that the scalar value shows up in the netcdf file, ...

That's a correct method, although if you're using Fortran as your P.S. says,
you must be using NCVPT1 and NCVGT1.  Also in the case of scalars it doesn't
matter what value you use for MINDEX since its value isn't needed so its
just a placeholder.

>                                                    ... but
> i just noticed that i'm unable to read it back in with 
> ncvarget or ncvarget1. it always returns zero instead of the
> scalar stored in the file. is this because i've screwed up?

Maybe, although I'd have to see an example of how are trying
to access the data to be sure.

> do i have to define scalar variables as one dimensional variables
> whose dimension length is one? 

No, scalars are 0-dimensional variables and they don't have a dimension
length.

> an example would be helpful

OK, here's a Fortran example that reads and writes a scalar value:

      program fexample
      include 'netcdf.inc'
      integer  iret
* netCDF id
      integer  cdfid
* variable ids
      integer  zid
* data variables
      real z
* enter define mode
      cdfid = nccre ('z.nc', NCCLOB, iret)
* define variables
      zid = ncvdef (cdfid, 'z', NCFLOAT, 0, 0, iret)
* leave define mode
      call ncendf(cdfid, iret)
* store into z.  It doesn't matter what the mindex argument is for a scalar, so 
we
* just use "0" for a placeholder
      call ncvpt1(cdfid, zid, 0, 3.14159, iret)
* read from netCDF scalar variable
      call ncvgt1(cdfid, zid, 0, z, iret)
* verify value was read correctly
      print *, z
      end

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