dump_nc4_metadata.c File Reference

Read a NetCDF-4 file and print all metadata including user-defined types. 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_str (int ncid, nc_type xtype, char *buf, size_t buflen)
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)
static int	print_user_types (int ncid, const char *indent)
static int	print_group (int ncid, const char *group_name, const char *indent)
int	main (int argc, char *argv[])

Detailed Description

Read a NetCDF-4 file and print all metadata including user-defined types.

This example demonstrates how to use the NetCDF-4 inquiry functions to discover and print all metadata in a NetCDF-4 file without prior knowledge of its contents. It reads a filename from the command line, opens the file, and prints:

• User-defined types (compound, enum, vlen, opaque)
• All dimensions (name and length, noting unlimited dimensions)
• All global attributes (name, type, and value)
• All variables (name, type, dimensions, and attributes)
• Groups (recursively)

This extends the classic dump_classic_metadata example with NetCDF-4 features.

Learning Objectives:

• Use nc_inq_typeids() to discover user-defined types in a group
• Use nc_inq_user_type() to determine type class (compound, enum, vlen, opaque)
• Use nc_inq_compound(), nc_inq_enum(), nc_inq_vlen(), nc_inq_opaque() for details
• Use nc_inq_grps() to discover child groups
• Recursively traverse the group hierarchy
• Build generic inspection tools for NetCDF-4 files with complex structure

Key Concepts:

• User-Defined Types: Types beyond atomic (compound, enum, vlen, opaque)
• Type Discovery: nc_inq_typeids() returns all type IDs in a group
• Type Classes: NC_COMPOUND, NC_ENUM, NC_VLEN, NC_OPAQUE identified by nc_inq_user_type()
• Group Hierarchy: nc_inq_grps() returns child group IDs for recursive traversal
• Recursive Pattern: Process root group, then recurse into each child group
• NC_GLOBAL in Groups: Each group has its own global attributes, accessed via group ncid
• Type Scope: User-defined types are visible in their defining group and descendants

Prerequisites:

• dump_classic_metadata.c - Classic metadata inspection pattern
• groups.c - Understanding group hierarchy
• user_types.c - Understanding user-defined types

Related Examples:

• dump_classic_metadata.c - Simpler version for classic files
• user_types.c - Creates a file with all four user-defined type classes
• groups.c - Creates a file with nested groups suitable for inspection

Compilation:

gcc -o dump_nc4_metadata dump_nc4_metadata.c -lnetcdf

Usage:

./dump_nc4_metadata user_types.nc

Expected Output: Prints all metadata from the specified NetCDF-4 file:

• User-defined types with class, size, and member details
• Dimensions (with unlimited flagged) per group
• Global attributes per group
• Variables with types, dimensions, and per-variable attributes
• Recursive output for all child groups

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

print_group()

static int print_group ( int  ncid, const char *  group_name, const char *  indent  )

static

print_user_types()

static int print_user_types ( int  ncid, const char *  indent  )

static

type_name_str()

static const char * type_name_str ( int  ncid, nc_type  xtype, char *  buf, size_t  buflen  )

static