multi_unlimited.c File Reference

Demonstrates multiple unlimited dimensions (NetCDF-4 feature) More...

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

Macros
#define	FILE_NAME   "multi_unlimited.nc"
#define	INITIAL_STATIONS   3
#define	INITIAL_TIMES   5
#define	ADDED_STATIONS   2
#define	ADDED_TIMES   3
#define	NDIMS   2
#define	ERRCODE   2
#define	ERR(e)   {printf("Error: %s\n", nc_strerror(e)); exit(ERRCODE);}

Functions
int	main ()

Detailed Description

Demonstrates multiple unlimited dimensions (NetCDF-4 feature)

This example showcases one of NetCDF-4's key enhancements over classic NetCDF: the ability to have multiple unlimited dimensions. While classic NetCDF allows only one unlimited dimension, NetCDF-4 supports any number, enabling more flexible data structures for complex datasets.

The program creates a file with two unlimited dimensions (station and time), writes initial data, then demonstrates appending data along both dimensions. This pattern is common in observational data where both the number of stations and timesteps can grow over time.

Learning Objectives:

• Understand multiple unlimited dimensions in NetCDF-4
• Learn to create variables with multiple unlimited dimensions
• Master appending data along different unlimited dimensions
• Work with ragged arrays and sparse datasets
• Recognize when multiple unlimited dimensions are beneficial

Key Concepts:

• Multiple Unlimited Dimensions: NetCDF-4 allows unlimited dimensions in any position
• Classic Limitation: Classic NetCDF allows only one unlimited dimension (first position)
• Ragged Arrays: Arrays where one dimension varies for each index of another
• Sparse Data: Data where not all dimension combinations have values
• Dynamic Growth: Dimensions can grow independently

Use Cases for Multiple Unlimited Dimensions:

• Observational Networks: Stations and time both grow
• Ensemble Forecasts: Ensemble members and forecast times both unlimited
• Particle Tracking: Particles and timesteps both grow
• Sparse Matrices: Rows and columns both unlimited
• Event Data: Multiple event types and times

Design Considerations:

• Only available in NetCDF-4 format (not classic)
• Can impact performance due to chunking requirements
• Consider whether both dimensions truly need to be unlimited
• Alternative: Use fixed dimensions with generous sizes

Prerequisites:

• unlimited_dim.c - Single unlimited dimension basics
• simple_nc4.c - NetCDF-4 format requirements
• var4d.c - Multi-dimensional data concepts

Related Examples:

• f_multi_unlimited.f90 - Fortran equivalent
• unlimited_dim.c - Single unlimited dimension (classic compatible)
• chunking_performance.c - Chunking with unlimited dimensions

Compilation:

gcc -o multi_unlimited multi_unlimited.c -lnetcdf -lm

Usage:

./multi_unlimited
ncdump multi_unlimited.nc

Expected Output: Creates multi_unlimited.nc containing:

• 2 unlimited dimensions: station(UNLIMITED), time(UNLIMITED)
• Variable: temperature(station, time)
• Demonstrates growth from 3×5 to 5×8 array
• Shows appending along both dimensions independently

Author

Edward Hartnett, Intelligent Data Design, Inc.

Date

2026

Macro Definition Documentation

ADDED_STATIONS

#define ADDED_STATIONS   2

ADDED_TIMES

#define ADDED_TIMES   3

ERR

#define ERR

(

e

)

{printf("Error: %s\n", nc_strerror(e)); exit(ERRCODE);}

ERRCODE

#define ERRCODE   2

FILE_NAME

#define FILE_NAME   "multi_unlimited.nc"

INITIAL_STATIONS

#define INITIAL_STATIONS   3

INITIAL_TIMES

#define INITIAL_TIMES   5

NDIMS

#define NDIMS   2

Function Documentation

main()

int main

(

)