dump_classic_metadata.c File Reference

Read a NetCDF file and print all metadata (dimensions, variables, attributes) More...

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

Macros
#define	ERRCODE   2
#define	ERR(e)   {printf("Error: %s\n", nc_strerror(e)); return ERRCODE;}

Functions
static const char *	type_name (nc_type xtype)
static int	print_att_value (int ncid, int varid, const char *att_name, nc_type xtype, size_t len)
static int	print_attributes (int ncid, int varid, int natts, const char *indent)
int	main (int argc, char *argv[])

Detailed Description

Read a NetCDF file and print all metadata (dimensions, variables, attributes)

This example demonstrates how to use the NetCDF inquiry functions to discover and print all metadata in a NetCDF file without prior knowledge of its contents. It reads a filename from the command line, opens the file, and prints:

• All dimensions (name and length, noting unlimited dimensions)
• All global attributes (name, type, and value)
• All variables (name, type, dimensions, and attributes)

This is a useful pattern for building tools that inspect arbitrary NetCDF files.

Learning Objectives:

• Use nc_inq() to discover file structure without prior knowledge
• Iterate over dimensions with nc_inq_dim() and detect unlimited dimensions
• Iterate over variables with nc_inq_var() to get type, shape, and attribute count
• Iterate over attributes with nc_inq_att() and nc_inq_attname()
• Read attribute values of different types (text, numeric, arrays)
• Handle unlimited dimensions specially in output
• Build generic file inspection tools using only inquiry functions

Key Concepts:

• Inquiry Functions: nc_inq_*() family discovers file contents at runtime
• Variable Iteration: Loop from varid=0 to nvars-1 to visit all variables
• Attribute Iteration: Loop from attnum=0 to natts-1 for each variable or NC_GLOBAL
• Type Discovery: nc_inq_att() returns nc_type for proper value interpretation
• Unlimited Dimension: Detected by comparing dimid to nc_inq_unlimdim() result
• NC_GLOBAL: Special varid constant for accessing global (file-level) attributes
• Generic Tool Pattern: Read structure first, then interpret — enables tools that work on any NetCDF file regardless of contents

Prerequisites:

• simple_2D.c - Basic NetCDF file operations
• coord_vars.c - Understanding of dimensions, variables, and attributes

Related Examples:

• dump_nc4_metadata.c - Extended version with NetCDF-4 groups and user types
• coord_vars.c - Creates a file suitable for inspection with this tool
• coord.c - Creates a 3D file with more metadata to explore

Compilation:

gcc -o dump_classic_metadata dump_classic_metadata.c -lnetcdf

Usage:

./dump_classic_metadata coord_vars.nc

Expected Output: Prints all metadata from the specified file:

• Dimensions with names and lengths (unlimited flagged)
• Global attributes with names, types, and values
• Variables with names, types, dimension lists, and per-variable attributes

Note

Companion code for "The NetCDF Developer's Handbook: The Authoritative Guide to Writing High-Performance Programs for Scientific Data Management, Second Edition" (https://www.amazon.com/dp/B0H7Q1Z75L)

Author

Edward Hartnett, Intelligent Data Design, Inc.

Date

2026

Macro Definition Documentation

ERR

#define ERR

(

e

)

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

ERRCODE

#define ERRCODE   2

Function Documentation

main()

int main	(	int	argc,
		char *	argv[]
	)

print_att_value()

static int print_att_value ( int  ncid, int  varid, const char *  att_name, nc_type  xtype, size_t  len  )

static

print_attributes()

static int print_attributes ( int  ncid, int  varid, int  natts, const char *  indent  )

static

type_name()

static const char * type_name ( nc_type  xtype )

static