nczarr_enhanced.c File Reference

Demonstrate the NetCDF-4 enhanced data model in a local NcZarr dataset. More...

#include <netcdf.h>
#include <stdio.h>
#include <stdlib.h>

Macros
#define	FILE_URL   "file://nczarr_enhanced.zarr#mode=nczarr"
#define	NX   5
#define	NTIMES   2
#define	NSTATIONS   3
#define	ERR(e)

Functions
int	main (void)

Detailed Description

Demonstrate the NetCDF-4 enhanced data model in a local NcZarr dataset.

This example extends nczarr_compression.c by introducing two enhanced-model features that are unavailable in classic NetCDF: hierarchical groups and multiple independent unlimited dimensions. The same nc_def_grp() and NC_UNLIMITED APIs used for NetCDF-4/HDF5 files work identically with NcZarr.

The program creates a NcZarr store with a root group containing a time (unlimited) × x(5) grid of temperature and pressure variables, and a child group obs/ that holds its own independent station (unlimited) dimension with observation value and time-index variables. After writing, the program reopens the store, navigates to the child group by name, verifies that both unlimited dimensions grew independently, and validates all data values.

Learning Objectives:

• Create a named child group inside a NcZarr root group with nc_def_grp()
• Define an unlimited dimension independently in a child group
• Show that root and child group unlimited dimensions grow separately
• Navigate to a child group on reopen with nc_inq_grp_ncid()
• Understand which enhanced-model features NcZarr supports: groups and unlimited dims are fully supported; user-defined types (enum, compound) require HDF5 storage and are not available in NcZarr

Key Concepts:

• nc_def_grp(): Creates a named child group; all subsequent def calls on the returned group ID are scoped to that group
• NC_UNLIMITED in a child group: Each group tracks its own record dimension independently — appending to obs/station does not affect root/time and vice versa
• nc_inq_grp_ncid(): Retrieves a child group ID by name after reopen; needed to access dimensions and variables scoped to that group
• nc_put_vara_float() / nc_put_vara_int(): Write a contiguous slab to an unlimited variable; start[] and count[] control the written region

Related Examples:

• nczarr_simple.c - Basic NcZarr create/read/write (flat, no groups)
• nczarr_chunking.c - Explicit chunk shape selection
• nczarr_compression.c - Deflate + shuffle compression
• examples/netcdf-4/groups.c - Deep group hierarchy with HDF5 storage

Compilation:

gcc -o nczarr_enhanced nczarr_enhanced.c -lnetcdf

Usage:

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

Expected Output: Creates the directory nczarr_enhanced.zarr containing:

• Root group: 2 dimensions (time=unlimited, x=5), 2 variables (temperature(time,x), pressure(time,x)), units attributes, global title
• Child group obs/: 1 dimension (station=unlimited), 2 variables (obs_value(station) in Celsius, obs_time(station)), group description
• 2 time steps written to root; 3 station records written to obs/

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

2026-06-27

Macro Definition Documentation

ERR

#define ERR

(

e

)

Value:

    do { \
    if (e) { \
        fprintf(stderr, "Error: %s at line %d\n", nc_strerror(e), __LINE__); \
        return 1; \
    } \
} while(0)

FILE_URL

#define FILE_URL   "file://nczarr_enhanced.zarr#mode=nczarr"

NSTATIONS

#define NSTATIONS   3

NTIMES

#define NTIMES   2

NX

#define NX   5

Function Documentation

main()

int main

(

void

)