format_variants.c File Reference

Demonstrates all five NetCDF binary format variants. More...

#include <stdio.h>
#include <stdlib.h>
#include <netcdf.h>
#include <sys/stat.h>

Macros
#define	NTIME   10
#define	NLAT   20
#define	NLON   30
#define	ERRCODE   2
#define	ERR(e)   {printf("Error: %s\n", nc_strerror(e)); exit(ERRCODE);}

Functions
long	get_file_size (const char *filename)
void	populate_file (int ncid)
void	verify_format_file (const char *filename, int expected_format, const char *expected_format_name)
int	main ()

Detailed Description

Demonstrates all five NetCDF binary format variants.

This example creates identical data structures in all five NetCDF binary formats to illustrate their differences in file size limits, compatibility, storage backend, and use cases. Understanding format variants is crucial for choosing the right format for your data requirements.

The program creates five files with the same 3D temperature and pressure data (time×lat×lon) in different formats, then compares their characteristics including file size, format detection, and size limitations.

Learning Objectives:

• Understand all five NetCDF binary format variants
• Learn when to use each format based on size requirements
• Master format detection with nc_inq_format() and nc_inq_format_extended()
• Compare file sizes and format overhead
• Make informed format choices for different use cases

Key Concepts:

• NC_CLOBBER (CDF-1): Original NetCDF format, 2GB limits (default, no format flag needed)
• NC_64BIT_OFFSET (CDF-2): Extended format with 4GB variable limit
• NC_64BIT_DATA (CDF-5): Modern format with unlimited variable sizes
• NC_NETCDF4: NetCDF-4/HDF5 format with groups, compression, user types
• NC_NETCDF4|NC_CLASSIC_MODEL: HDF5 storage with classic data model
• NC_CLASSIC_MODEL: Only used with NC_NETCDF4 to restrict to classic data model
• Format Detection: Runtime identification of file format
• Backward Compatibility: Older formats work with all NetCDF versions

Format Comparison:

Format	File Limit	Variable Limit	NetCDF Version	Backend	Use Case
CDF-1	2GB	2GB	3.0+	CDF	Maximum compatibility (default)
CDF-2	Unlimited	4GB	3.6.0+	CDF	Large files, moderate variables
CDF-5	Unlimited	Unlimited	4.4.0+	CDF	Very large variables
NC4	Unlimited	Unlimited	4.0+	HDF5	Full NetCDF-4 features
NC4/CM	Unlimited	Unlimited	4.0+	HDF5	HDF5 storage, classic model

Prerequisites:

• simple_2D.c - Basic file creation
• simple_nc4.c - NetCDF-4 basics

Related Examples:

• f_format_variants.f90 - Fortran equivalent
• size_limits.c - Demonstrates actual size limits
• compression.c - NetCDF-4 compression features

Compilation:

gcc -o format_variants format_variants.c -lnetcdf

Usage:

./format_variants
ls -lh format_*.nc
ncdump -h format_classic.nc

Expected Output: Creates five files:

• format_classic.nc (CDF-1)
• format_64bit_offset.nc (CDF-2)
• format_64bit_data.nc (CDF-5)
• format_netcdf4.nc (NetCDF-4/HDF5)
• format_netcdf4_classic.nc (NetCDF-4 Classic Model) All contain identical data with similar file sizes for this small dataset.

Author

Edward Hartnett, Intelligent Data Design, Inc.

Date

2026

Macro Definition Documentation

ERR

#define ERR

(

e

)

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

ERRCODE

#define ERRCODE   2

NLAT

#define NLAT   20

NLON

#define NLON   30

NTIME

#define NTIME   10

Function Documentation

get_file_size()

long get_file_size

(

const char *

filename

)

main()

int main

(

)

populate_file()

void populate_file

(

int

ncid

)

verify_format_file()

void verify_format_file	(	const char *	filename,
		int	expected_format,
		const char *	expected_format_name
	)