var4d.c File Reference

Demonstrates multi-dimensional arrays (2D, 3D, 4D) with dimension reuse. More...

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

Macros
#define	FILE_NAME   "var4d.nc"
#define	NTIME   3
#define	NLEVEL   2
#define	NLAT   4
#define	NLON   5
#define	ERRCODE   2
#define	ERR(e)   {printf("Error: %s\n", nc_strerror(e)); exit(ERRCODE);}

Functions
int	main ()

Detailed Description

Demonstrates multi-dimensional arrays (2D, 3D, 4D) with dimension reuse.

This example shows how to work with multi-dimensional scientific data by creating variables of different dimensionalities (2D, 3D, 4D) that share common dimensions. This pattern is typical in atmospheric and oceanographic data where variables have different spatial and temporal coverage.

The program creates a file with 4 dimensions (time, level, lat, lon) and three temperature variables: surface temperature (2D), temperature profile (3D), and full 3D atmospheric temperature (4D). This demonstrates dimension reuse and efficient file organization.

Learning Objectives:

• Understand multi-dimensional array indexing in NetCDF
• Learn dimension reuse across multiple variables
• Master 4D array creation and access patterns
• Work with atmospheric/oceanographic data structures
• Understand C row-major vs NetCDF dimension ordering

Key Concepts:

• Dimension Reuse: Same dimension used by multiple variables
• Dimension Ordering: NetCDF uses slowest-to-fastest varying (time, level, lat, lon)
• C Array Indexing: Row-major order [time][level][lat][lon]
• Variable Dimensionality: Variables can use subsets of available dimensions
• Atmospheric Levels: Vertical coordinate (pressure, height, sigma)

Dimension Ordering Convention:

• NetCDF convention: (time, level, lat, lon) - slowest to fastest varying
• C array declaration: [time][level][lat][lon] - matches NetCDF order
• Fortran array declaration: (lon, lat, level, time) - reversed from C
• Access pattern: data[t][lev][i][j] for time t, level lev, lat i, lon j

Prerequisites:

• simple_2D.c - Basic 2D arrays
• coord_vars.c - Coordinate variables
• unlimited_dim.c - Time dimension concepts

Related Examples:

• f_var4d.f90 - Fortran equivalent (note dimension order reversal)
• coord_vars.c - 2D geospatial data
• unlimited_dim.c - Time-series data

Compilation:

gcc -o var4d var4d.c -lnetcdf

Usage:

./var4d
ncdump var4d.nc

Expected Output: Creates var4d.nc containing:

• 4 dimensions: time(3), level(2), lat(4), lon(5)
• 3 variables with different dimensionalities:
  • temp_surface(lat, lon) - 2D surface temperature
  • temp_profile(time, lat, lon) - 3D time-varying surface
  • temp_3d(time, level, lat, lon) - 4D full atmosphere

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

FILE_NAME

#define FILE_NAME   "var4d.nc"

NLAT

#define NLAT   4

NLEVEL

#define NLEVEL   2

NLON

#define NLON   5

NTIME

#define NTIME   3

Function Documentation

main()

int main

(

)