nccmp : NetCDF Compare

nccmp

Overview
Download
Installation
Examples
Usage
News
References

Overview

nccmp compares two NetCDF files bitwise, semantically or with a user defined tolerance (absolute or relative percentage). Parallel comparisons are done in local memory without requiring temporary files. Highly recommended for regression testing scientific models or datasets in a test-driven development environment.

Here's an incomplete list of reasons why you may want to check your data:

Change in architecture (hardware, bare-metal, virtualization, platform, operating system).
Change in compiler, compiler options or dependent libraries.
Code refactoring, language migration, algorithm evolution, replacement or optimization.
Data type promotion or demotion, compression, shuffling, alignment, ordering, encoding, metadata, or schema change.
Process model change (framework, order of execution, partitioning).
Tuning model parameters.
Up/down-sampling fitness.

Features

Multi-threaded if posix threads are supported on your system.
Prints differences and their locations (C or Fortran indexing). Format precision is customizable and allows hex.
Specific variable inclusion or exclusion.
Specific groups by short or full (absolute) names, or all (including recursive groups).
Metadata and/or data comparisons.
Global attributes compared with or without the history attribute.
Exits when first difference is found or optionally continues to process all variables and/or attributes by force, or up to a global or per-variable count.
Attribute exclusion when comparing metadata.
Bitwise compare or with tolerances (absolute or relative).
Header padding contents and attribute comparisons for NetCDF3 classic/64bit file formats.
NaN values can be treated as equal (in case you use NaN's as grid masks).
Compare or dump encodings for one or both files: checksumming, chunking, compression, endianness, format, shuffling, and header-pad sizes.
Support all Netcdf4/HDF atomic types (char/text, schar, uchar, short, ushort, int, uint, int64, uint64, float, double, string) and user-defined types (enumeration, compound, opaque blob, variable-length array) and nesting.
Compare asymmetric atomic data type values, within variable-length arrays too. For example, a variable can be uint in the first file, and int64 in the second.
Compare similarly named compound fields and ignore differently named or missing fields, so compound schemas may have variation in field type, field order and field existence.
Asymmetric enum value and datatype semantics. Enum identifiers are compared instead of their encoded values, so your dataset schema can evolve flexibly without worrying about enum order, size, type, or numeric values, although any metadata differences will be reported.
Print data difference statistics (count, sum, absolute sum, min, max, range, mean, stdev) for numeric variables and compound fields. In quiet mode, only this summary table will print.
Lightweight. Comparing multi-gigabyte files will only consume several megabytes of arena memory.

Multithreading

Static scheduling is used for threads. Each thread will compare every time-varying variable over thread-strided record indices. Threading is optional, and configure will determine if POSIX threads are available.

Header Pad

In order to compare the contents of header pads, it is required to download the NetCDF source code and configure nccmp using --with-netcdf=dir in order to access the private netcdf API. This is optional, and nccmp can be built without this feature.

Download

Binaries

Ubuntu 12, 14, 15

$ sudo add-apt-repository ppa:remik-ziemlinski/nccmp && \
  sudo apt-get update && \
  sudo apt-get install nccmp

Windows

# 64-bit
$ wget https://downloads.sourceforge.net/project/nccmp/windows/x86_64/nccmp-1.8.0.0-msys2-x86_64.zip

Cygwin - Windows

Run either setup-x86.exe or setup-x86_64.exe, and select All => Science => nccmp.

Mac OSX Homebrew

$ brew tap homebrew/science
$ brew install nccmp
$ brew test nccmp

Source

nccmp-1.8.0.0.tar.gz

$ cd /tmp && \
  wget -nd -c http://prdownloads.sourceforge.net/nccmp/nccmp-1.8.0.0.tar.gz && \
  tar zxvf nccmp-*.tar.gz

Installation

Linux/Unix/MacPorts/Anaconda


# (Optional) Download the NetCDF source code to support header-pad comparisons.
$ cd /tmp && \
  wget -nd -c http://www.unidata.ucar.edu/downloads/netcdf/ftp/netcdf-4.3.3.1.tar.gz && \
  tar zxvf netcdf-*.tar.gz

# Specify non-standard installation locations for HDF and NetCDF, 
# if not auto-detected by configure (i.e. they're not in /usr/local/{include,lib}).
$ HDF=/usr/local/hdf5-1.8.15-patch1
$ NC=/usr/local/netcdf-4.3.3.1
$ export CFLAGS="-I$HDF/include -I$NC/include"
$ export LDFLAGS="-L$HDF/lib -L$NC/lib"

$ tar zxvf nccmp-*.tgz && cd nccmp-*
$ ./configure --with-netcdf=/tmp/netcdf-4.3.3.1 --enable-test-big
...
configure:

    CFLAGS             = -I/usr/local/hdf5-1.8.15-patch1/include -I/usr/local/netcdf-4.3.3.1/include -pthread
    CPPFLAGS           = 
    enable-test-big    = yes
    HAVE_NC_H          = yes
    HAVE_NC_INQ_PATH   = yes
    HAVE_PTHREAD       = yes
    LDFLAGS            = -L/usr/local/hdf5-1.8.15-patch1/lib -L/usr/local/netcdf-4.3.3.1/lib -pthread
    LIBS               = -lnetcdf -lm 
    with-netcdf        = /usr/local/netcdf-4.3.3.1/src


$ make -j4
$ make check
$ make install-strip
$ make clean
$ man nccmp

Cygwin - Windows


$ C:/cygwin/setup-x86.exe

# Install these prebuilt binary cygwin packages via the setup GUI:
# All => Libs  => libnetcdf7      v4.3.3.1-2
#              => libnetcdf-devel v4.3.3.1-2
#              => netcdf          v4.3.3.1-2

$ ./configure --with-netcdf=/cygdrive/c/Temp/netcdf-4.3.3.1
$ make
$ make check
$ make install

MSYS2 - Windows


$ pacman -S make man gcc diffutils

# Download and run Netcdf Windows installer:
# http://www.unidata.ucar.edu/software/netcdf/docs/winbin.html

$ NC=/d/netCDF-4.3.3.1/ 
$ export PATH=$PATH:$NC/bin
$ ./configure CFLAGS=-I$NC/include LDFLAGS=-L$NC/bin --enable-test-big
$ make
$ make check
$ make install
$ man nccmp
$ nccmp --version
Configuration
Date    = Wed Sep 30 13:48:00 EDT 2015
Host    = MSYS_NT-6.1 rszhp 2.3.0(0.290/5/3) 2015-09-15 09:39 x86_64 Msys
NetCDF  = 4.3.1-rc4 of Apr 13 2014 18:53:57 $
User    = rsz
Flags   = CC="gcc" \
          CFLAGS="-I/d/netCDF-4.3.3.1//include " \
          CPP="gcc -E" \
          CPPFLAGS="" \
          LDFLAGS="-L/d/netCDF-4.3.3.1//bin " \
          LIBS="-lnetcdf -lm " \
          ./configure CFLAGS=-I/d/netCDF-4.3.3.1//include LDFLAGS=-L/d/netCDF-4.3.3.1//bin --enable-test-big

Mac OSX Homebrew


$ brew tap homebrew/science
$ brew install hdf5
$ brew install netcdf

$ NC=/usr/local/Cellar/netcdf/4.3.3.1_1
$ export CFLAGS="-I$NC/include"
$ export CPPFLAGS="$CFLAGS"
$ export LDFLAGS="-L$NC/lib"
$ export DYLD_LIBRARY_PATH="$DYLD_LIBRARY_PATH":$NC/lib

$ ./configure --with-netcdf=/Users/rsz/source/netcdf-4.3.3.1
$ make
$ make check
$ make install

Testing


$ make check
make  check-TESTS
make[3]: Entering directory `/home/rsz/projects/nccmp/nccmp-code/test'
PASS: test_nccmp_setup.sh
PASS: test_nccmp_strlist
PASS: test_nccmp_odometer
PASS: test_nccmp_user_type
PASS: test_nccmp_01.sh
...
PASS: test_nccmp_68.sh
PASS: test_big.sh
make[4]: Entering directory `/home/rsz/projects/nccmp/nccmp-code/test'
make[4]: Nothing to be done for `all'.
make[4]: Leaving directory `/home/rsz/projects/nccmp/nccmp-code/test'
============================================================================
Testsuite summary for nccmp 1.8.0.0
============================================================================
# TOTAL: 75
# PASS:  75
# SKIP:  0
# XFAIL: 0
# FAIL:  0
# XPASS: 0
# ERROR: 0

Memory correctness is tested with valgrind. Leaks will print red colored errors.


$ cd test &&
  ./memcheck.sh

Examples

There are 68 examples in the test/ directory.


# Compare metadata for non-record variables.
$ nccmp -mf -x recdata,rec test1a.nc test1b.nc
DIFFER : NUMBER OF DIMENSIONS IN FILES : 5 <> 4
DIFFER : LENGTHS : DIMENSION : dim3 : 2 <> 1
DIFFER : DIMENSION : dim4 : DOES NOT EXIST IN "test1b.nc"
DIFFER : VARIABLE : data3 : DOES NOT EXIST IN "test1b.nc"
DIFFER : DIMENSION NAMES FOR VARIABLE "data4" : dim4 <> dim2
DIFFER : VARIABLE "data1" IS MISSING ATTRIBUTE WITH NAME "units" IN FILE "test1b.nc"
DIFFER : LENGTHS : ATTRIBUTE : long_name : VARIABLE : data1 : 9 <> 10 : VALUES : "test data" : "test data_"
DIFFER : VARIABLE : data1 : ATTRIBUTE : valid_range : VALUES : 1,2 <> -2,1
DIFFER : NUMBER OF ATTRIBUTES : VARIABLE : data1 : 3 <> 2

# Compare data using a tolerance threshold.
$ nccmp -df -t 1e-3 test4a.nc test4b.nc
DIFFER : VARIABLE : data1 : POSITION : [0,1] : VALUES : 2 <> 2.01 : PERCENT : 0.497512
DIFFER : VARIABLE : data2 : POSITION : [0,1] : VALUES : 8 <> 7.99 : PERCENT : 0.125003
DIFFER : VARIABLE : data3 : POSITION : [0] : VALUES : 9 <> 8 : PERCENT : 11.1111
DIFFER : VARIABLE : data3 : POSITION : [1] : VALUES : 10 <> -10 : PERCENT : 200
DIFFER : VARIABLE : data4 : POSITION : [0] : VALUES : 11 <> 110 : PERCENT : 90
DIFFER : VARIABLE : recdata1 : POSITION : [0,1] : VALUES : 4 <> 0 : PERCENT : 100
DIFFER : VARIABLE : recdata2 : POSITION : [0,0] : VALUES : a <> c : PERCENT : 2.0202
DIFFER : VARIABLE : rec : POSITION : [1] : VALUES : 6 <> 6.1 : PERCENT : 1.63934

# Compare data written in different formats (classic vs. HDF).
$ nccmp -dmgfb test1a.nc test1c.nc 
2015-09-11 16:42:16.955951 -0400 INFO nccmp.c:135 Command-line options parsed.
2015-09-11 16:42:16.955951 -0400 INFO nccmp.c:43 Opening input files.
2015-09-11 16:42:16.955951 -0400 INFO nccmp_state.c:130 Opening test1a.nc
2015-09-11 16:42:16.955951 -0400 INFO nccmp_state.c:130 Opening test1c.nc
2015-09-11 16:42:16.955951 -0400 INFO nccmp.c:81 Comparing file formats.
DIFFER : FILE FORMATS : NC_FORMAT_CLASSIC <> NC_FORMAT_NETCDF4
2015-09-11 16:42:16.955951 -0400 INFO nccmp.c:95 Comparing groups.
2015-09-11 16:42:16.955951 -0400 INFO nccmp_group.c:50 Comparing groups "/" and "/".
2015-09-11 16:42:16.955951 -0400 INFO nccmp_metadata.c:1458 Comparing global attributes.
2015-09-11 16:42:16.955951 -0400 INFO nccmp_group.c:60 Collecting dimension information for first group.
2015-09-11 16:42:16.955951 -0400 INFO nccmp_group.c:67 Collecting dimension information for second group.
2015-09-11 16:42:16.955951 -0400 INFO nccmp_group.c:74 Collecting variable information for group id = 65536.
2015-09-11 16:42:16.955951 -0400 INFO nccmp_var.c:338 "rec" missing value: 0 (float)
2015-09-11 16:42:16.955951 -0400 INFO nccmp_group.c:81 Found 6 variables in first group.
2015-09-11 16:42:16.955951 -0400 INFO nccmp_group.c:82 Collecting variable information for group id = 131072.
2015-09-11 16:42:16.955951 -0400 INFO nccmp_var.c:338 "rec" missing value: 0 (float)
2015-09-11 16:42:16.955951 -0400 INFO nccmp_group.c:89 Found 6 variables in second group.
2015-09-11 16:42:16.955951 -0400 INFO nccmp_var.c:173 Using all variables.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_var.c:182 Variables to compare (6): data1, data2, data3, data4, recdata, rec
2015-09-11 16:42:16.965951 -0400 INFO nccmp_metadata.c:1800 Comparing record information.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_metadata.c:245 Comparing metadata.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_metadata.c:304 Comparing number of dimensions.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_metadata.c:1403 Getting record dimension names, if they exist.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_metadata.c:327 Comparing dimension lengths.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_metadata.c:930 Comparing user defined types.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_metadata.c:987 Comparing variable datatypes and rank.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_metadata.c:1054 Comparing variable dimension names.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_metadata.c:1120 Comparing variables attributes.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3522 Comparing data.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_var.c:232 Validating variable data1.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_var.c:232 Validating variable data2.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_var.c:232 Validating variable data3.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_var.c:232 Validating variable data4.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_var.c:232 Validating variable recdata.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_var.c:232 Validating variable rec.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3441 Thread 0 comparing non-record data for variable data1.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3441 Thread 0 comparing non-record data for variable data2.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3441 Thread 0 comparing non-record data for variable data3.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3441 Thread 0 comparing non-record data for variable data4.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3443 Thread 0 comparing data for variable recdata at record 0.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3443 Thread 0 comparing data for variable recdata at record 1.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3443 Thread 0 comparing data for variable rec at record 0.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3443 Thread 0 comparing data for variable rec at record 1.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3443 Thread 0 comparing data for variable rec at record 1.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_data.c:3552 Finished comparing data.
2015-09-11 16:42:16.965951 -0400 INFO nccmp_group.c:126 Group comparison complete.
2015-09-11 16:42:16.965951 -0400 INFO nccmp.c:108 Comparisons complete.

# Compare identical files.
$ nccmp -dmgfs test1a.nc test1a.nc 
Files "test1a.nc" and "test1a.nc" are identical.

# Get some info on file structure internals.
$ nccmp -i encoded.nc
path=encoded.nc
format=NC_FORMAT_NETCDF4
header_size=0 bytes
header_pad_size=0 bytes
var=var1 checksum=NC_FLETCHER32 chunk=NC_CHUNKED chunksizes=[2] deflate=1 deflate_level=5 endian=NC_ENDIAN_BIG shuffle=1 szip_mask=0 szip_pixels_per_block=0

# Compare opaque user defined type (3-byte blobs).
$ nccmp -mdf test13a.nc test13b.nc
DIFFER : TYPE : opaq2 : SIZE : 3 <> 4
DIFFER : VARIABLE : var2 : POSITION : [1] : VALUES : 0x0A0B0C <> 0x0D0E0F
DIFFER : VARIABLE : var3 : POSITION : [1,0] : VALUES : 0x000004 <> 0x040004
DIFFER : VARIABLE : var3 : POSITION : [1,1] : VALUES : 0x000005 <> 0x000505
DIFFER : VARIABLE : var3 : POSITION : [1,2] : VALUES : 0x000006 <> 0x000066

# Compare nested compound field arrays of user types.
$ nccmp -df make_compound_array_user_type1.nc make_compound_array_user_type2.nc
DIFFER : VARIABLE : var1 : POSITION : [0,0,1,1,1,1,1] : FIELD : i : VALUES : 115 <> 215
DIFFER : VARIABLE : var1 : POSITION : [0,0,1,1,0,1,1] : FIELD : myString : VALUES : bl <> cl
DIFFER : VARIABLE : var1 : POSITION : [0,0,1,1,1,0,0] : FIELD : myEnum : VALUES : FOO <> BAR
DIFFER : VARIABLE : var1 : POSITION : [0,0,0] : FIELD : myVlen[1,1,1,1] : VARIABLE LENGTH : 1 <> 2
DIFFER : VARIABLE : var1 : POSITION : [0,0,0] : FIELD : myVlen[1,1,1,1][0] : VALUES : 16 <> 17
DIFFER : VARIABLE : var1 : POSITION : [0,0,1] : FIELD : myComp[1,1,0,1].myLongLong[1,0,0,1] : VALUES : 1014009 <> 2014009

# Print statistics and hide diff messages.
$ nccmp -dfqS test21a.68.nc test21b.68.nc

Variable         Group           Count     Sum AbsSum     Min     Max  Range    Mean   StdDev
var1             /                   2      -3      3      -2      -1      1    -1.5 0.707107
var2.com2.com1.i /                   2     -30     30     -20     -10     10     -15  7.07107
var3.com2.com1.i /group              2    -300    300    -200    -100    100    -150  70.7107
var4.f           /group              1   -1000   1000   -1000   -1000      0   -1000        0
var4.s           /group              1  -10000  10000  -10000  -10000      0  -10000        0
var5.com2.com1.i /group/subgroup     2 -300000 300000 -200000 -100000 100000 -150000  70710.7

Usage

Compare two NetCDF files.
nccmp is silent when files are equivalent, otherwise it will echo to STDERR whether metadata or a specific variable differs.  By default, comparing stops after the first difference.

Exit code 0 is returned for identical files, 1 for different files, and 2 for a fatal error.

Usage: nccmp [OPTION...] file1 [file2]

  -A, --Attribute=att1[,...] Ignore attribute(s) att1[,...]
                             for all variables.
  -b, --verbose              Print messages to show progress.
  -c, --var-diff-count=COUNT Stop comparing a variable after COUNT data diffs.
  -C, --diff-count=COUNT     Stop comparing after COUNT data diffs total.
  -d, --data                 Compare data (variable values).
  -D, --debug                Prints verbose debug messages.
  -e, --encoding             Compare these variable encoding settings:
                             checksum, chunk, deflate, endianness, shuffle, szip
  -f, --force                Forcefully compare, do not stop after first
                             difference.
  -F, --fortran              Print position indices using Fortran style
                             (1-based reverse order).
  -g, --global               Compare global attributes.
                             (auto enables -m)
  -G, --globalex att1[,...]  Exclude global attributes att1[,...].
                             (auto enables -g)
  -h, --history              Compare global history attribute.
                             (auto enables -g)
  -H, --help                 Give this usage message.
      --usage                
  -i, --info                 Print file structure info for one or both files.
  -l, --color                Print colored messages.
  -m, --metadata             Compare metadata.
                             Use -g to include global attributes.
  -M, --missing              Ignore difference between values that have
                             different missing_value and/or _FillValue.
                             Attribute differences are still reported.
  -n, --threads=N            Use N POSIX threads. Default is 1.
  -N, --nans-are-equal       Allow NaNs to be equal.
  -p, --precision=FMT        Global precision of difference printing.
                             Use '%x' to print bytes.
                             FMT defaults differently per data type:
                                 double '%g'
                                 float  '%g'
                                 int    '%d'
                                 int64  '%lld'
                                 schar  '0x%02X'
                                 short  '%d'
                                 text   '%c'
                                 uchar  '0x%02X'
                                 uint   '%d'
                                 uint64 '%llu'
                                 ushort '%d'
  -P, --header-pad           Compare header padding in classic or 64bit
                             file formats.
  -q, --quiet                Do not print metadata or data differences.
  -r, --group=group1[,...]   Compare group(s) group1[,...] only.
                             Group names can be full or short.
  -s, --report-identical-files
                             Report when files are the same.
  -S, --statistics           Report data difference statistics.
  -t, --tolerance=TOL        Compare if absolute difference > TOL.
  -T, --Tolerance=TOL        Compare if relative percent difference > TOL.
  -v, --variable=var1[,...]  Compare variable(s) var1[,...] only.
  -V, --version              Print program version.
  -x, --exclude=var1[,...]   Exclude variable(s) var1[,...].
  -w, --warn=tag[,...]       Selectively make certain differences
                             exceptions, but still print messages.
                             Supported tags and their meanings:
                                 all: All differences.
                                 format: File formats.
                                 eos: Extra attribute end-of-string nulls.

Report bugs to Remik . Ziemlinski @ noaa . gov.
nccmp 1.8.0.0

Configuration
Date    = Fri Sep 25 12:42:16 EDT 2015
Host    = Linux mint 3.16.0-38-generic #52~14.04.1-Ubuntu SMP Fri May 8 09:43:57 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
NetCDF  = 4.3.3.1 of Jul  8 2015 09:51:52 $
User    = rsz
Flags   = CC="gcc" \
          CFLAGS="-I/usr/local/hdf5-1.8.15-patch1/include -I/usr/local/netcdf-4.3.3.1/include -pthread" \
          CPP="gcc -E" \
          CPPFLAGS="" \
          LDFLAGS="-L/usr/local/hdf5-1.8.15-patch1/lib -L/usr/local/netcdf-4.3.3.1/lib -pthread" \
          LIBS="-lnetcdf -lm " \
          ./configure --with-netcdf=/usr/local/netcdf-4.3.3.1/src --enable-test-big

Features
header-pad = yes
pthreads   = yes

News

Version 1.8.0.0 (12/25/2015)

1. Added -S, --statistics to print summary data table for numeric data diffs.
2. Added -q, --quiet to suppress diff messages.
3. Added -l, --color for colored printing.
4. Added arena memory for non-compound numeric variables.
5. Added cmake config to build executable.

Version 1.7.5.1 (10/2/2015)

1. Allow compiling and testing in arbitrary build directory outside source
directory tree to conform to Cygwin cygport build and check standards.

Version 1.7.5.0 (9/30/2015)

1. (MSYS Windows) Fix core dump from string-type deallocation and
close test data file handles.
2. Replace config.guess with latest git version to support MSYS2.

Version 1.7.4.1 (9/29/2015)

1. Make build process parallel to conform to Homebrew build standards.

Version 1.7.4.0 (9/27/2015)

1. Updated code and tests to support 32-bit (i386) architecture on Ubuntu.
2. Created Ubuntu 12,14,15 PPAs.

Version 1.7.3.0 (9/25/2015)

1. Adapted code and tests to support older Netcdf 4.1.1 as found on Ubuntu 12.

Version 1.7.2.0 (9/24/2015)

1. Additional configuration info printed with --version.
2. Fixed bug with handling group dimensions for NetCDF libraries before version 4.3.
3. Make advanced NetCDF4 test data creation backwards compatible with ncgen before version 4.3.

Version 1.7.1 (9/21/2015)

1. Fixed bug in regression test and verified on Ubuntu 14 with Anaconda 2.3.0,
thanks to Matt Savoie (NSIDC) for pointing out `make check` failures.

Version 1.7.0 (9/11/2015)

1. For HDF formatted files, compare variable encoding parameters for
chunking, deflating, endianness, checksumming, shuffling and szip
(-e, --encoding).
2. Support all new Netcdf4 atomic types:
ubyte, ushort, uint, int64, uint64, string.
3. Support user-defined types and nesting of enums, compounds, variable-length, opaque blobs.
4. Asymmetric type data comparisons. For example, you can compare a
variable defined as integer in the first file, and float in the second.
Use --force if initial metadata variable type comparisons fail.
5. Enable optional big file test when running `make check`
(./configure --enable-test-big).
6. Fixed segfault, all memory leaks and cleaned up scripts,
thanks to testing by Emma Hogan (UK MetOffice).

Version 1.6.1 (7/29/2015)

1. Added multithreading with posix threads
(-n, --threads=N).
2. Compare groups (and recursively) for all or by short or full name
(-r, --group=group1[,...]).
Thanks to Sean W. Bailey (NASA) and Rick Healy (NASA) for the idea and contributing code.
3. Dump file traits like shuffle, chunk, deflate, header-pad for one or
both input files, with no need to do compare
(-i, --info).
4. Limit comparisons and diff messages printed with global and/or per-variable count
(-c, --var-diff-count=CNT, -C, --diff-count=CNT).
Thanks to Sean W. Bailey (NASA) and Rick Healy (NASA) for the idea and contributing code.
5. Optionally build with header-pad and thread support, and print features enabled
with --version or --help.

Version 1.5.0 (11/30/2014)

1. Added new -N, --nans-are-equal option.
By default, NaN does not equal anything including itself.
Now you can override this definition when comparing floats or doubles
that might have NaNs.
Thanks to Bob Fischer for this request.
2. Added new -P, --header-pad option.
Some tools may alter the header pad after filtering classic/64bit NetCDF3 files.
These changes can now be detected.
Thanks to Andrew Wittenberg.

Version 1.4.0 (5/30/2013)

1. Added new -M,--missing option.
If both files have different missing_value and/or _FillValue,
consider them the same. Thanks to Dave Allured for the idea.

Version 1.3.0 (4/4/2013)

1. Added new warning flag (-w eos) to ignore extra end-of-string nulls in (global and variable) attribute strings (NC_CHAR type).
2. Added missing support for -D debug flag.

Version 1.2.0 (2/23/2013)

1. Added configure option --enable-ncinfo (default is yes). This will build and install the small helper tool. Use --enable-ncinfo=no to skip it.
2. Added new option (-s, --report-identical-files) to report when two files are the same, just like "diff". Will print a string like:
Files "foo.nc" and "bar.nc" are identical.
3. Created git repo.

Version 1.1.2 (2/10/2013)

1. Fixed building for macports (MacOSX 10.8, Xcode 4.6, gcc4.7.2). Thanks to Dave Allured.

Version 1.1.1 (9/24/2012)

1. Bugfix to handle HDF group dimensions with dimids that don't start at zero. Thanks to Lynton Appel.
2. Removed default build and install of 'ncinfo' because not core to nccmp mission. If you still need it, cd into the ncinfo subdir and do make there.

Version 1.1.0 (7/15/2010)

1. Added "-w, --warn" command-line option to make certain differences exceptions and only print messages of their occurance. Thanks to Aleksey Yakovlev.
2. Added a small helper program called 'ncinfo' that echoes a file's format, header size (NetCDF3 files only) and compression characteristics for NetCDF4 files.

Version 1.0.4 (6/27/2010)

1. Bug fix when comparing attributes when a variable was missing in a file. Thanks to Lionel Guez.
2. Pretty print attribute values when they differ.
3. Added simple utility "ncinfo" in /ncinfo to echo file's format and chunk/compression/header characteristics. Thanks to Aleksey Yakovlev.

Version 1.0.3 (4/13/2010)

1. Added hex printing.
2. Added custom precision of float/single value printing.
3. Added fortran-style index printing.

Version 1.0.2 (3/20/2010)

1. Fixed unsafe record queries.
2. Added more information "verbose" progress messages.
3. Made "quiet" mode from pre-1.0 deprecated by making option hidden although still accepted from command-line.

Version 1.0.1 (3/10/2010)

1. Fixed record-based scalar variable comparisons.

Version 1.0.0 (1/20/2010)

1. Overhauled to work generically with Netcdf4 at the cost of lower performance.

Version 0.6.0

1. Added new -G command-line option to ignore specific global attributes. Thanks to V. Balaji.

Version 0.5.4

1. Avoided reading past EOF when number of records differ between files. Record variables won't be compared as a result.
Users should use another tool, like "ncks" to extract record-based hyperslabs if they really need to compare partial netcdf files. Thanks to Lionel Guez.
2. Handles case when both files have record dimensions with length zero. Thanks to Lionel Guez.

Version 0.5.3

1. Fixed memory thrashing in string management code.
2. Made --enable-mpi configure argument and padded header testing more robust.

Version 0.5.2

1. Added command-line option to ignore specific variable attributes.

Version 0.5.1

1. Fixed bug. Single record variables were skipped.

Version 0.5.0

Thanks to Amy Langenhorst for suggestion 1.

1. Compare with absolute or relative percentage tolerance. Obviously slower due to arithmetic. No MPI support for tolerance feature.

Version 0.4.2

Thanks to Amy Langenhorst for these suggestions.

* forces removal of temporary files in generated view script.
* generated view script tests if there exists a user defined NCCMPDIFF,
otherwise sets it to 'diff' as default.
* suppresses global history attribute when extracting data in
generated view script.

Version 0.4.1

* bug fix: prevents premature file closing while still querying for
info such as when generating example view script.

Version 0.4

* builds nccmpi for usage with MPI enabled systems

Version 0.3

* ported completely to C; was a perl script originally

Version 0.2.1

* bug fix: check for comparisons beyond EOF
* bug fix: memory allocation for variable list

Version 0.2

* -q quiet mode, suppresses all but difference message
* -f force mode, process all variables possible; doesn't exit program
after 1st difference
* -x exclude variable list option
* enhanced view script

Version 0.1

* outputs script to do visual comparison of different values

References

NetCDF Data Format