NetCDF

3.6:

What’s

New

Russ Rew Unidata Program Center

University Corporation for Atmospheric Research2004-09-01

www.unidata.ucar.edu/packages/netcdf/

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2

Overview

•A new format variant

•Backward compatibility

•Refactored documentation

•File size limitations eliminated

•Better configuration support

•Better Windows support

•Bug fixes, performance enhancements

3

Larger netCDF files, 64-bit file offsets

•Current “classic” format uses 32-bit offsets

•New 64-bit offset format mode available on creation, for very large files:

nc_create(file, NC_64BIT_OFFSET, &ncid)

•Initial development by Greg Sjaardema, Sandia Labs

•We added:

Fortran, C++, ncgen, ncdump support

Extensive additional error checking

2GiB to 4GiB variable size increase

Elimination of 4GiB record size limit

4

Backward Compatibility•Version 3.6 library reads classic format

or new format transparently

•By default, new files are created in classic format

•New format should only be used for files too large for classic format

•No code changes needed for existing code

•Third-party software eventually should be upgraded to 3.6 to support new format

Refactored Documentation

•User’s Guides for C, FORTRAN-77, FORTRAN-90 converted from FrameMaker (proprietary) to Texinfo (GNU documentation system)

•Language-neutral User’s Guide documents data model and language-independent concepts

•Language-specific guides for C, Fortran-77, Fortran-90, and C++ interfaces

•Will support better maintenance of documentation, easier addition of other language-specific manuals

6

Elimination of some size limitations

LimitWithout Large File Support

(LFS)

NetCDF 3.5 with LFS

NetCDF 3.6 with LFS, classic

format

NetCDF 3.6 with LFS, 64-bit

offset format

Maximum file size 2 GiB 8 EiB 8 EiB 8 EiB

Maximum size of fixed variable, record size of record variable

2 GiB 2 GiB 2 GiB 4 GiB

Maximum record size2 GiB / nrecs

4 GiB 8 EiB / nrecs 8 EiB / nrecs

I GiB = 230 or about 1.07 109 bytes

I EiB = 260 or about 1.15 1018 bytes

7

Better configuration support

•Upgraded to use latest autoconf configuration tool

•Builds with Large File Support by default, if available

•Tested on more platforms with more development environments

Better Windows support

•Included with source distribution in win32 directory

•Added .Net port

•Builds with VC++.NET from source

•Added windows installer files to build windows binary installs

Performance enhancements, bug fixes

•Fortran -77 implementation upgraded with more recent cfortran.h

•Added -x option to ncgen to use fast “no fill” mode for netcdf file creation

•Fixed ncdump and ncgen to properly handle dimension lengths > 231

•Added new error codes for invalid dimension and variable size

•Added tests for invalid offsets in classic format

•Added performance fix for Fortran-90 array access interfaces