f_nczarr_chunking.f90 File Reference

Demonstrate chunked storage in a local NcZarr dataset (Fortran). More...

Functions/Subroutines
program	f_nczarr_chunking
subroutine	handle_err (status)

Detailed Description

Demonstrate chunked storage in a local NcZarr dataset (Fortran).

Fortran equivalent of nczarr_chunking.c. Creates a 4x5 temperature array with explicit chunk shape [2, 5] (y, x) in a local NcZarr store, verifies chunking metadata after reopening, and validates data values.

Learning Objectives:

• Set explicit chunk shape for a NcZarr variable from Fortran
• Query chunk metadata after reopen using nf90_inquire_variable
• Understand Fortran column-major chunksizes ordering

Key Concepts:

• nf90_def_var_chunking() sets chunk shape for NcZarr storage
• Fortran column-major: chunksizes(1)=CHUNK_X, chunksizes(2)=CHUNK_Y
• Chunking controls how data is split into Zarr chunk files
• Same nf90_def_var_chunking() API works for NetCDF-4/HDF5 and NcZarr

Fortran vs C Differences:

• Chunk dimensions reversed: Fortran chunksizes(1)=x, (2)=y vs C chunksizes[0]=y, [1]=x
• Uses nf90_inquire_variable(chunksizes=) instead of separate function

Related Examples:

• nczarr_chunking.c - C equivalent
• f_nczarr_simple.f90 - Basic NcZarr Fortran example
• f_nczarr_compression.f90 - Adding compression on top of chunking

Compilation:

gfortran -o f_nczarr_chunking f_nczarr_chunking.f90 -lnetcdff -lnetcdf

Usage:

./f_nczarr_chunking
ncdump 'file://f_nczarr_chunking.zarr#mode=nczarr'

Expected Output: Creates the directory f_nczarr_chunking.zarr containing:

• 2 dimensions: y(4), x(5)
• 1 variable: temperature(y, x) of type NF90_FLOAT with chunks [2, 5]
• Attributes: units="K", long_name="Temperature", _FillValue=-999.0
• A 4x5 temperature data grid stored in 2 chunks of 2x5 each

Note

Companion code for "The NetCDF Developer's Handbook: The Authoritative Guide to Writing High-Performance Programs for Scientific Data Management, Second Edition" (https://www.amazon.com/dp/B0H7Q1Z75L)

Author

Edward Hartnett, Intelligent Data Design, Inc.

Date

2026-06-26

Function/Subroutine Documentation

f_nczarr_chunking()

program f_nczarr_chunking

handle_err()

subroutine f_nczarr_chunking::handle_err

(

integer, intent(in)

status

)