unlimited_dim.c File Reference

Demonstrates unlimited dimensions for appendable time-series data. More...

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

Macros
#define	FILE_NAME   "unlimited_dim.nc"
#define	NLAT   4
#define	NLON   5
#define	INITIAL_TIMESTEPS   3
#define	APPEND_TIMESTEPS   2
#define	TOTAL_TIMESTEPS   (INITIAL_TIMESTEPS + APPEND_TIMESTEPS)
#define	ERRCODE   2
#define	ERR(e)   {printf("Error: %s\n", nc_strerror(e)); exit(ERRCODE);}

Functions
int	main ()

Detailed Description

Demonstrates unlimited dimensions for appendable time-series data.

This example introduces unlimited dimensions - a special dimension type that can grow dynamically, allowing data to be appended to files over time. Unlimited dimensions are essential for time-series data where the total number of timesteps is not known in advance.

The program creates a file with an unlimited time dimension, writes initial timesteps, then reopens the file in write mode to append additional timesteps. This demonstrates the common pattern for incrementally building time-series datasets.

Learning Objectives:

• Understand unlimited dimensions and their use cases
• Learn to create files with NC_UNLIMITED dimension
• Master appending data to existing files
• Work with time-series data patterns
• Understand performance implications of unlimited dimensions

Key Concepts:

• Unlimited Dimension: Dimension that can grow (NC_UNLIMITED)
• Record Variable: Variable with unlimited dimension as first dimension
• Appending Data: Adding new records to existing file
• Time Series: Sequential data indexed by time
• File Reopening: Opening existing file for modification (NC_WRITE)

Unlimited Dimension Characteristics:

• Only one unlimited dimension allowed in classic formats
• Must be the first (slowest-varying) dimension of record variables
• Enables incremental data writing without knowing final size
• Slightly slower than fixed dimensions due to dynamic allocation
• NetCDF-4 allows multiple unlimited dimensions

Prerequisites:

• simple_2D.c - Basic file and variable operations
• coord_vars.c - Multi-dimensional data

Related Examples:

• f_unlimited_dim.f90 - Fortran equivalent
• multi_unlimited.c - Multiple unlimited dimensions (NetCDF-4)
• var4d.c - 4D data with time dimension

Compilation:

gcc -o unlimited_dim unlimited_dim.c -lnetcdf

Usage:

./unlimited_dim
ncdump unlimited_dim.nc

Expected Output: Creates unlimited_dim.nc containing:

• Unlimited time dimension (grows from 3 to 5 records)
• Fixed lat(4) and lon(5) dimensions
• Temperature variable(time, lat, lon)
• Demonstrates appending 2 additional timesteps

Author

Edward Hartnett, Intelligent Data Design, Inc.

Date

2026

Macro Definition Documentation

APPEND_TIMESTEPS

#define APPEND_TIMESTEPS   2

ERR

#define ERR

(

e

)

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

ERRCODE

#define ERRCODE   2

FILE_NAME

#define FILE_NAME   "unlimited_dim.nc"

INITIAL_TIMESTEPS

#define INITIAL_TIMESTEPS   3

NLAT

#define NLAT   4

NLON

#define NLON   5

TOTAL_TIMESTEPS

#define TOTAL_TIMESTEPS   (INITIAL_TIMESTEPS + APPEND_TIMESTEPS)

Function Documentation

main()

int main

(

)