format_variants.c File Reference

Demonstrates NetCDF classic format variants (CDF-1, CDF-2, CDF-5) 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	create_format_file (const char *filename, int format_flag, const char *format_name)
void	verify_format_file (const char *filename, const char *expected_format_name)
int	main ()

Detailed Description

Demonstrates NetCDF classic format variants (CDF-1, CDF-2, CDF-5)

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

The program creates three 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 the three classic NetCDF 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_CLASSIC_MODEL (CDF-1): Original NetCDF format, 2GB limits
• NC_64BIT_OFFSET (CDF-2): Extended format with 4GB variable limit
• NC_64BIT_DATA (CDF-5): Modern format with unlimited variable sizes
• 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	Use Case
CDF-1	2GB	2GB	3.0+	Maximum compatibility
CDF-2	Unlimited	4GB	3.6.0+	Large files, moderate variables
CDF-5	Unlimited	Unlimited	4.4.0+	Very large variables

Prerequisites:

• simple_2D.c - Basic file creation
• coord_vars.c - Variable and attribute definitions

Related Examples:

• f_format_variants.f90 - Fortran equivalent
• size_limits.c - Demonstrates actual size limits
• simple_nc4.c - NetCDF-4/HDF5 format (different architecture)

Compilation:

gcc -o format_variants format_variants.c -lnetcdf

Usage:

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

Expected Output: Creates three files:

• format_classic.nc (CDF-1)
• format_64bit_offset.nc (CDF-2)
• format_64bit_data.nc (CDF-5) 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

create_format_file()

void create_format_file	(	const char *	filename,
		int	format_flag,
		const char *	format_name
	)

get_file_size()

long get_file_size

(

const char *

filename

)

main()

int main

(

)

verify_format_file()

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