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20040728: netCDF: solaris - mixed programming, C and Fortran

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  • Subject: 20040728: netCDF: solaris - mixed programming, C and Fortran
  • Date: Tue, 03 Aug 2004 17:39:01 -0600
>From: "ufuk utku turuncoglu" <address@hidden>
>Organization: Istanbul Technical University
>Keywords: 200407281433.i6SEX60H002441 netCDF file format

Ufuk,

>Institution: istanbul technical university
>Package Version: 3.5
>Operating System: solaris
>Hardware Information: sunfire 12 k
>Inquiry: hi,

I apologize that I have not been able to get to your inquiry before today.

>i generate a netcdf file using C program but when i read the netcdf data from 
>fortran, it comes wrong. I think, fortran (column) and c (row) stores array
>differently in memory and this generates problem.

Yes, the Fortran and C conventions for array elements is different.

>Is it possible to read data without any conversion (such as intercahage
>the data to fortran stored format)?

Data is written to a netCDF file using the C convention and it matches
the convention used in CDLs.

Here are two comments from the netCDF Users Guide:

 ...

  "In FORTRAN, the dimensions are reversed from the CDL declaration
  with the first dimension varying fastest and the record dimension
  as the last dimension of a record variable."

 ...

  "Different dimension orders for the C, FORTRAN, or other language
  interfaces do not reflect a different order for values stored on the
  disk, but merely different orders supported by the procedural
  interfaces to the languages.  In general, it does not matter whether
  a netCDF dataset is written using the C, FORTRAN, or other language
  interface; netCDF datasets written from any supported language may be
  read by programs in other supported languages."

This means that you need to read data back from a netCDF making
adjustments for the interface (C or Fortran) you are using.  You do
not, however, have to worry about how the file was created.

>If not, it means that netcdf formats depends on the creator programming
>language and it is not possible to always have information about it.

The format in the file does not depend on the language the developer
was using; it is always done the same.

>Is there way that solve the mixed language problem?

Yes, you need to read the data from a netCDF knowing that it is written
using the array ordering of C.

>Why the netcdf library handles of this problem? 

The storage ordering matches the CDL syntax ordering which matches the
C ordering and that, in turn, matches the ordering in memory. It is
unfortunate that C and FORTRAN don't use the same ordering for array
elements in memory; programmers must take that into account when doing
mixed language programming.

In order to become better familiar with the issues involved, I would
suggest reviewing:

NetCDF User's Guide for C
http://my.unidata.ucar.edu/content/software/netcdf/guidec/index.html

NetCDF User's Guide for FORTRAN
http://my.unidata.ucar.edu/content/software/netcdf/guidef/index.html

>best regards,

Cheers,

Tom Yoksas
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