\input texinfo @c -*-texinfo-*-
@comment This is part of the netCDF documentation. See COPYRIGHT file
@c $Id: netcdf-f90.texi,v 1.61 2010/03/25 15:26:06 ed Exp $
@c %**start of header
@setfilename netcdf-f90.info
@settitle NetCDF Fortran 90 Interface Guide
@setcontentsaftertitlepage
@c Combine the variable, concept, and function indices.
@synindex vr cp
@synindex fn cp
@c %**end of header

@c version.texi is automatically generated by automake and contains
@c defined variables VERSION, UPDATED, UPDATED-MONTH.
@include version-f90.texi
@include defines.texi

@ifinfo
@dircategory netCDF scientific data format
@direntry
* netcdf-f90: (netcdf-f90).         @value{f90-man}
@end direntry
@end ifinfo

@titlepage
@title @value{f90-man}
@subtitle NetCDF Version @value{VERSION}
@subtitle @value{UPDATED}
@author Robert Pincus
@author Russ Rew
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@ifnottex
@node Top, Use of the NetCDF Library, (dir), (dir)
@top @value{f90-man}

This document describes the Fortran 90 interface to the netCDF
library. It applies to netCDF version @value{VERSION}. This document
was last updated in @value{UPDATED}.

For a complete description of the netCDF format and utilities see 
@ref{Top, @value{n-man},, netcdf, @value{n-man}}.

@end ifnottex

@menu
* Use of the NetCDF Library::   
* Datasets::                    
* Groups::                      
* Dimensions::                  
* User Defined Data Types::     
* Variables::                   
* Attributes::                  
* Summary of Fortran 90 Interface::  
* Fortran 77 to Fortran 90 Transition Guide::  
* Combined Index::              

@detailmenu
 --- The Detailed Node Listing ---

Use of the NetCDF Library

* Creating a NetCDF Dataset::   
* Reading a NetCDF Dataset with Known Names::  
* Reading a netCDF Dataset with Unknown Names::  
* Writing Data in an Existing NetCDF Dataset::  
* Adding New Dimensions::       
* Error Handling::              
* Compiling and Linking with the NetCDF Library::  

Datasets

* Datasets Introduction::       
* NetCDF Library Interface Descriptions::  
* NF90_STRERROR::               
* NF90_INQ_LIBVERS::            
* NF90_CREATE::                 
* NF90_OPEN::                   
* NF90_REDEF::                  
* NF90_ENDDEF::                 
* NF90_CLOSE::                  
* NF90_INQUIRE Family::         
* NF90_SYNC::                   
* NF90_ABORT::                  
* NF90_SET_FILL::               

Groups

* NF90_INQ_NCID::               
* NF90_INQ_GRPS::               
* NF90_INQ_VARIDS::             
* NF90_INQ_DIMIDS::             
* NF90_INQ_GRPNAME_LEN::        
* NF90_INQ_GRPNAME::            
* NF90_INQ_GRPNAME_FULL::       
* NF90_INQ_GRP_PARENT::         
* NF90_INQ_GRP_NCID::           
* NF90_INQ_GRP_FULL_NCID::      
* NF90_DEF_GRP::                

Dimensions

* Dimensions Introduction::     
* NF90_DEF_DIM::                
* NF90_INQ_DIMID::              
* NF90_INQUIRE_DIMENSION::      
* NF90_RENAME_DIM::             

User Defined Data Types

* User Defined Types::          
* NF90_INQ_TYPEIDS::            
* nf90_inq_typeid::             
* NF90_INQ_TYPE::               
* NF90_INQ_USER_TYPE::          
* Compound Types::              
* Variable Length Array::       
* Opaque Type::                 
* Enum Type::                   

Example

* NF90_PUT_VLEN_ELEMENT::       
* NF90_GET_VLEN_ELEMENT::       

Compound Types Introduction

* NF90_DEF_COMPOUND::           
* NF90_INSERT_COMPOUND::        
* NF90_INSERT_ARRAY_COMPOUND::  
* NF90_INQ_COMPOUND::           
* NF90_INQ_COMPOUND_FIELD::     

Variable Length Array Introduction

* NF90_DEF_VLEN::               
* NF90_INQ_VLEN::               
* NF90_FREE_VLEN::              

Opaque Type Introduction

* NF90_DEF_OPAQUE::             
* NF90_INQ_OPAQUE::             

Example

* NF90_INQ_OPAQUE::               

Enum Type Introduction

* NF90_DEF_ENUM::               
* NF90_INSERT_ENUM::            
* NF90_INQ_ENUM::               
* NF90_INQ_ENUM_MEMBER::        
* NF90_INQ_ENUM_IDENT::         

Variables

* Variables Introduction::      
* Language-Types::              
* NF90_DEF_VAR::                Create a Variable
* NF90_DEF_VAR_FILL::           
* NF90_INQ_VAR_FILL::           
* NF90_INQUIRE_VARIABLE::       Get Var Metadata
* NF90_INQ_VARID::              
* NF90_PUT_VAR::                Write data
* NF90_GET_VAR::                Read data
* Reading and Writing Character String Values::  
* Fill Values::                 What's Written Where there's No Data?
* NF90_RENAME_VAR::             
* NF90_VAR_PAR_ACCESS::         

Attributes

* Attributes Introduction::     
* NF90_PUT_ATT::                
* NF90_INQUIRE_ATTRIBUTE::      
* NF90_GET_ATT::                
* NF90_COPY_ATT::               
* NF90_RENAME_ATT::             
* NF90_DEL_ATT::                

@end detailmenu
@end menu

@node Use of the NetCDF Library, Datasets, Top, Top
@chapter Use of the NetCDF Library
@cindex users' guide, netcdf
@cindex common netcdf commands

You can use the netCDF library without knowing about all of the netCDF
interface. If you are creating a netCDF dataset, only a handful of
routines are required to define the necessary dimensions, variables,
and attributes, and to write the data to the netCDF dataset. (Even
less are needed if you use the ncgen utility to create the dataset
before running a program using netCDF library calls to write
data. @xref{ncgen,,,netcdf, NetCDF Users Guide}.)
Similarly, if you are writing software to access data stored in a
particular netCDF object, only a small subset of the netCDF library is
required to open the netCDF dataset and access the data. Authors of
generic applications that access arbitrary netCDF datasets need to be
familiar with more of the netCDF library.

In this chapter we provide templates of common sequences of netCDF
calls needed for common uses. For clarity we present only the names of
routines; omit declarations and error checking; omit the type-specific
suffixes of routine names for variables and attributes; indent
statements that are typically invoked multiple times; and use ... to
represent arbitrary sequences of other statements. Full parameter
lists are described in later chapters.


@menu
* Creating a NetCDF Dataset::   
* Reading a NetCDF Dataset with Known Names::  
* Reading a netCDF Dataset with Unknown Names::  
* Writing Data in an Existing NetCDF Dataset::  
* Adding New Dimensions::       
* Error Handling::              
* Compiling and Linking with the NetCDF Library::  
@end menu

@node Creating a NetCDF Dataset, Reading a NetCDF Dataset with Known Names, Use of the NetCDF Library, Use of the NetCDF Library
@section Creating a NetCDF Dataset
@cindex dataset, creating
@findex NF90_CREATE, typical use
@findex NF90_DEF_DIM, typical use
@findex NF90_DEF_VAR, typical use
@findex NF90_PUT_ATT, typical use
@findex NF90_ENDDEF, typical use
@findex NF90_PUT_VAR, typical use
@findex NF90_CLOSE, typical use

Here is a typical sequence of netCDF calls used to create a new netCDF
dataset: 

@example
     NF90_CREATE           ! create netCDF dataset: enter define mode
          ... 
        NF90_DEF_DIM       ! define dimensions: from name and length
          ... 
        NF90_DEF_VAR       ! define variables: from name, type, dims
          ... 
        NF90_PUT_ATT       ! assign attribute values
          ... 
     NF90_ENDDEF           ! end definitions: leave define mode
          ... 
        NF90_PUT_VAR       ! provide values for variable
          ... 
     NF90_CLOSE            ! close: save new netCDF dataset
@end example

Only one call is needed to create a netCDF dataset, at which point you
will be in the first of two netCDF modes. When accessing an open
netCDF dataset, it is either in define mode or data mode. In define
mode, you can create dimensions, variables, and new attributes, but
you cannot read or write variable data. In data mode, you can access
data and change existing attributes, but you are not permitted to
create new dimensions, variables, or attributes.

One call to NF90_DEF_DIM is needed for each dimension
created. Similarly, one call to NF90_DEF_VAR is needed for each
variable creation, and one call to a member of the NF90_PUT_ATT family
is needed for each attribute defined and assigned a value. To leave
define mode and enter data mode, call NF90_ENDDEF.

Once in data mode, you can add new data to variables, change old
values, and change values of existing attributes (so long as the
attribute changes do not require more storage space). Data of all
types is written to a netCDF variable using the NF90_PUT_VAR
subroutine. Single values, arrays, or array sections may be supplied
to NF90_PUT_VAR; optional arguments allow the writing of subsampled or
mapped portions of the variable. (Subsampled and mapped access are
general forms of data access that are explained later.)

Finally, you should explicitly close all netCDF datasets that have
been opened for writing by calling NF90_CLOSE. By default, access to
the file system is buffered by the netCDF library. If a program
terminates abnormally with netCDF datasets open for writing, your most
recent modifications may be lost. This default buffering of data is
disabled by setting the NF90_SHARE flag when opening the dataset. But
even if this flag is set, changes to attribute values or changes made
in define mode are not written out until NF90_SYNC or NF90_CLOSE is
called.


@node Reading a NetCDF Dataset with Known Names, Reading a netCDF Dataset with Unknown Names, Creating a NetCDF Dataset, Use of the NetCDF Library
@section Reading a NetCDF Dataset with Known Names
@findex NF90_OPEN, typical use
@findex NF90_INQ_DIMID, typical use
@findex NF90_INQ_VARID, typical use
@findex NF90_GET_ATT, typical use
@findex NF90_GET_VAR, typical use

Here we consider the case where you know the names of not only the
netCDF datasets, but also the names of their dimensions, variables,
and attributes. (Otherwise you would have to do "inquire" calls.) The
order of typical C calls to read data from those variables in a netCDF
dataset is:

@example
     NF90_OPEN               ! open existing netCDF dataset
          ... 
        NF90_INQ_DIMID       ! get dimension IDs
          ... 
        NF90_INQ_VARID       ! get variable IDs
          ... 
        NF90_GET_ATT         ! get attribute values
          ... 
        NF90_GET_VAR         ! get values of variables
          ... 
     NF90_CLOSE              ! close netCDF dataset
@end example

First, a single call opens the netCDF dataset, given the dataset name,
and returns a netCDF ID that is used to refer to the open netCDF
dataset in all subsequent calls.

Next, a call to NF90_INQ_DIMID for each dimension of interest gets the
dimension ID from the dimension name. Similarly, each required
variable ID is determined from its name by a call to
NF90_INQ_VARID. Once variable IDs are known, variable attribute values
can be retrieved using the netCDF ID, the variable ID, and the desired
attribute name as input to NF90_GET_ATT for each desired
attribute. Variable data values can be directly accessed from the
netCDF dataset with calls to NF90_GET_VAR.

Finally, the netCDF dataset is closed with NF90_CLOSE. There is no
need to close a dataset open only for reading.

@node Reading a netCDF Dataset with Unknown Names, Writing Data in an Existing NetCDF Dataset, Reading a NetCDF Dataset with Known Names, Use of the NetCDF Library
@section Reading a netCDF Dataset with Unknown Names
@cindex reading dataset with unknown names
@findex NF90_INQUIRE, typical use
@findex NF90_INQUIRE_DIMENSION, typical use
@findex NF90_INQUIRE_VARIABLE, typical use
@findex NF90_INQUIRE_ATTRIBUTE, typical use
@findex NF90_INQ_ATTNAME, typical use
@findex NF90_GET_ATT, typical use

It is possible to write programs (e.g., generic software) which do
such things as processing every variable, without needing to know in
advance the names of these variables. Similarly, the names of
dimensions and attributes may be unknown.

Names and other information about netCDF objects may be obtained from
netCDF datasets by calling inquire functions. These return information
about a whole netCDF dataset, a dimension, a variable, or an
attribute. The following template illustrates how they are used:

@example
     NF90_OPEN                 ! open existing netCDF dataset
       ... 
     NF90_INQUIRE              ! find out what is in it
          ... 
        NF90_INQUIRE_DIMENSION ! get dimension names, lengths
          ... 
        NF90_INQUIRE_VARIABLE  ! get variable names, types, shapes
             ... 
           NF90_INQ_ATTNAME    ! get attribute names
             ... 
           NF90_INQUIRE_ATTRIBUTE ! get other attribute information
             ... 
           NF90_GET_ATT        ! get attribute values
             ... 
        NF90_GET_VAR           ! get values of variables
          ... 
     NF90_CLOSE                ! close netCDF dataset
@end example

As in the previous example, a single call opens the existing netCDF
dataset, returning a netCDF ID. This netCDF ID is given to the
NF90_INQUIRE routine, which returns the number of dimensions, the
number of variables, the number of global attributes, and the ID of
the unlimited dimension, if there is one.

All the inquire functions are inexpensive to use and require no I/O,
since the information they provide is stored in memory when a netCDF
dataset is first opened.

Dimension IDs use consecutive integers, beginning at 1. Also
dimensions, once created, cannot be deleted. Therefore, knowing the
number of dimension IDs in a netCDF dataset means knowing all the
dimension IDs: they are the integers 1, 2, 3, ...up to the number of
dimensions. For each dimension ID, a call to the inquire function
NF90_INQUIRE_DIMENSION returns the dimension name and length.

Variable IDs are also assigned from consecutive integers 1, 2, 3,
... up to the number of variables. These can be used in
NF90_INQUIRE_VARIABLE calls to find out the names, types, shapes, and
the number of attributes assigned to each variable.

Once the number of attributes for a variable is known, successive
calls to NF90_INQ_ATTNAME return the name for each attribute given the
netCDF ID, variable ID, and attribute number. Armed with the attribute
name, a call to NF90_INQUIRE_ATTRIBUTE returns its type and
length. Given the type and length, you can allocate enough space to
hold the attribute values. Then a call to NF90_GET_ATT returns the
attribute values.

Once the IDs and shapes of netCDF variables are known, data values can
be accessed by calling NF90_GET_VAR.

@node Writing Data in an Existing NetCDF Dataset, Adding New Dimensions, Reading a netCDF Dataset with Unknown Names, Use of the NetCDF Library
@section Writing Data in an Existing NetCDF Dataset 
@findex NF90_INQ_VARID, typical use
@findex NF90_PUT_VAR, typical use
@findex NF90_PUT_ATT, typical use
@cindex writing to existing dataset

With write access to an existing netCDF dataset, you can overwrite
data values in existing variables or append more data to record
variables along the unlimited (record) dimension. To append more data
to non-record variables requires changing the shape of such variables,
which means creating a new netCDF dataset, defining new variables with
the desired shape, and copying data. The netCDF data model was not
designed to make such "schema changes" efficient or easy, so it is
best to specify the shapes of variables correctly when you create a
netCDF dataset, and to anticipate which variables will later grow by
using the unlimited dimension in their definition.

The following code template lists a typical sequence of calls to
overwrite some existing values and add some new records to record
variables in an existing netCDF dataset with known variable names:

@example
     NF90_OPEN             ! open existing netCDF dataset
       ... 
       NF90_INQ_VARID      ! get variable IDs
       ... 
       NF90_PUT_VAR        ! provide new values for variables, if any
       ... 
       NF90_PUT_ATT        ! provide new values for attributes, if any
         ... 
     NF90_CLOSE            ! close netCDF dataset
@end example

A netCDF dataset is first opened by the NF90_OPEN call. This call puts
the open dataset in data mode, which means existing data values can be
accessed and changed, existing attributes can be changed, but no new
dimensions, variables, or attributes can be added.

Next, calls to NF90_INQ_VARID get the variable ID from the name, for
each variable you want to write. Then each call to NF90_PUT_VAR writes
data into a specified variable, either a single value at a time, or a
whole set of values at a time, depending on which variant of the
interface is used. The calls used to overwrite values of non-record
variables are the same as are used to overwrite values of record
variables or append new data to record variables. The difference is
that, with record variables, the record dimension is extended by
writing values that don't yet exist in the dataset. This extends all
record variables at once, writing "fill values" for record variables
for which the data has not yet been written (but @pxref{Fill Values}
to specify different behavior).

Calls to NF90_PUT_ATT may be used to change the values of existing
attributes, although data that changes after a file is created is
typically stored in variables rather than attributes.

Finally, you should explicitly close any netCDF datasets into which
data has been written by calling NF90_CLOSE before program
termination. Otherwise, modifications to the dataset may be lost.

@node Adding New Dimensions, Error Handling, Writing Data in an Existing NetCDF Dataset, Use of the NetCDF Library
@section Adding New Dimensions, Variables, Attributes
@cindex dimensions, adding
@cindex variables, adding
@cindex attributes, adding
@findex NF90_REDEF, typical use

An existing netCDF dataset can be extensively altered. New dimensions,
variables, and attributes can be added or existing ones renamed, and
existing attributes can be deleted. Existing dimensions, variables,
and attributes can be renamed. The following code template lists a
typical sequence of calls to add new netCDF components to an existing
dataset:

@example
     NF90_OPEN             ! open existing netCDF dataset
       ... 
     NF90_REDEF            ! put it into define mode
         ... 
       NF90_DEF_DIM        ! define additional dimensions (if any)
         ... 
       NF90_DEF_VAR        ! define additional variables (if any)
         ... 
       NF90_PUT_ATT        ! define other attributes (if any)
         ... 
     NF90_ENDDEF           ! check definitions, leave define mode
         ... 
       NF90_PUT_VAR        ! provide new variable values
         ... 
     NF90_CLOSE            ! close netCDF dataset
@end example

A netCDF dataset is first opened by the NF90_OPEN call. This call puts
the open dataset in data mode, which means existing data values can be
accessed and changed, existing attributes can be changed (so long as
they do not grow), but nothing can be added. To add new netCDF
dimensions, variables, or attributes you must enter define mode, by
calling NF90_REDEF. In define mode, call NF90_DEF_DIM to define new
dimensions, NF90_DEF_VAR to define new variables, and NF90_PUT_ATT to
assign new attributes to variables or enlarge old attributes.

You can leave define mode and reenter data mode, checking all the new
definitions for consistency and committing the changes to disk, by
calling NF90_ENDDEF. If you do not wish to reenter data mode, just
call NF90_CLOSE, which will have the effect of first calling
NF90_ENDDEF.

Until the NF90_ENDDEF call, you may back out of all the redefinitions
made in define mode and restore the previous state of the netCDF
dataset by calling NF90_ABORT. You may also use the NF90_ABORT call to
restore the netCDF dataset to a consistent state if the call to
NF90_ENDDEF fails. If you have called NF90_CLOSE from definition mode
and the implied call to NF90_ENDDEF fails, NF90_ABORT will
automatically be called to close the netCDF dataset and leave it in
its previous consistent state (before you entered define mode).

At most one process should have a netCDF dataset open for writing at
one time. The library is designed to provide limited support for
multiple concurrent readers with one writer, via disciplined use of
the NF90_SYNC function and the NF90_SHARE flag. If a writer makes
changes in define mode, such as the addition of new variables,
dimensions, or attributes, some means external to the library is
necessary to prevent readers from making concurrent accesses and to
inform readers to call NF90_SYNC before the next access.

@node Error Handling, Compiling and Linking with the NetCDF Library, Adding New Dimensions, Use of the NetCDF Library
@section Error Handling
@cindex error handling
@findex NF90_STRERROR, introduction

The netCDF library provides the facilities needed to handle errors in
a flexible way. Each netCDF function returns an integer status
value. If the returned status value indicates an error, you may handle
it in any way desired, from printing an associated error message and
exiting to ignoring the error indication and proceeding (not
recommended!). For simplicity, the examples in this guide check the
error status and call a separate function to handle any errors.

The NF90_STRERROR function is available to convert a returned integer
error status into an error message string.

Occasionally, low-level I/O errors may occur in a layer below the
netCDF library. For example, if a write operation causes you to exceed
disk quotas or to attempt to write to a device that is no longer
available, you may get an error from a layer below the netCDF library,
but the resulting write error will still be reflected in the returned
status value.

@node Compiling and Linking with the NetCDF Library,  , Error Handling, Use of the NetCDF Library
@section Compiling and Linking with the NetCDF Library
@cindex linking to netCDF library
@cindex compiling with netCDF library

Details of how to compile and link a program that uses the netCDF C or
Fortran interfaces differ, depending on the operating system, the
available compilers, and where the netCDF library and include files
are installed. 

Every Fortran 90 procedure or module which references netCDF constants
or procedures must have access to the module information created when
the netCDF module was compiled. The suffix for this file is ``MOD''
(or sometimes ``mod''). 

Most F90 compilers allow the user to specify the location of .MOD
files, usually with the -I flag. (Some compilers, like absoft, use -p
instead).

@example
f90 -c -I/usr/local/include mymodule.f90
@end example


Starting with version 3.6.2, another method of building the netCDF
Fortran libraries becomes available. With the
--enable-separate-fortran option to configure, the user can specify
that the C library should not contain the Fortran functions. In these
cases an additional library, libnetcdff.a (note the extra ``f'') will
be built. This library contains the Fortran functions.

For more information about configure options, @xref{Specifying the
Environment for Building,,, netcdf-install, @value{i-man}}.

Building separate Fortran libraries is required for shared library
builds, but is not done, by default, for static library builds.

When linking Fortran programs without a separate Fortran library,
programs must link to the netCDF library like this:

@example
f90 -o myprogram myprogram.o -L/usr/local/netcdf/lib -lnetcdf
@end example

@node Datasets, Groups, Use of the NetCDF Library, Top
@chapter Datasets

@menu
* Datasets Introduction::       
* NetCDF Library Interface Descriptions::  
* NF90_STRERROR::               
* NF90_INQ_LIBVERS::            
* NF90_CREATE::                 
* NF90_OPEN::                   
* NF90_REDEF::                  
* NF90_ENDDEF::                 
* NF90_CLOSE::                  
* NF90_INQUIRE Family::         
* NF90_SYNC::                   
* NF90_ABORT::                  
* NF90_SET_FILL::               
@end menu

@node Datasets Introduction, NetCDF Library Interface Descriptions, Datasets, Datasets
@section Datasets Introduction
@cindex datasets, overview

This chapter presents the interfaces of the netCDF functions that deal
with a netCDF dataset or the whole netCDF library.

A netCDF dataset that has not yet been opened can only be referred to
by its dataset name. Once a netCDF dataset is opened, it is referred
to by a netCDF ID, which is a small nonnegative integer returned when
you create or open the dataset. A netCDF ID is much like a file
descriptor in C or a logical unit number in Fortran. In any single
program, the netCDF IDs of distinct open netCDF datasets are
distinct. A single netCDF dataset may be opened multiple times and
will then have multiple distinct netCDF IDs; however at most one of
the open instances of a single netCDF dataset should permit
writing. When an open netCDF dataset is closed, the ID is no longer
associated with a netCDF dataset.

Functions that deal with the netCDF library include:
@itemize

@item
Get version of library. 

@item
Get error message corresponding to a returned error code. 
@end itemize

The operations supported on a netCDF dataset as a single object are:
@itemize

@item
Create, given dataset name and whether to overwrite or not. 

@item
Open for access, given dataset name and read or write intent. 

@item
Put into define mode, to add dimensions, variables, or attributes.

@item
Take out of define mode, checking consistency of additions. 

@item
Close, writing to disk if required. 

@item
Inquire about the number of dimensions, number of variables, number of
global attributes, and ID of the unlimited dimension, if any.

@item
Synchronize to disk to make sure it is current. 

@item
Set and unset nofill mode for optimized sequential writes. 

@item
After a summary of conventions used in describing the netCDF
interfaces, the rest of this chapter presents a detailed description
of the interfaces for these operations.
@end itemize

@node NetCDF Library Interface Descriptions, NF90_STRERROR, Datasets Introduction, Datasets
@section NetCDF Library Interface Descriptions
@cindex interface descriptions

Each interface description for a particular netCDF function in this
and later chapters contains:

@itemize

@item
a description of the purpose of the function; 

@item
a Fortran 90 interface block that presents the type and order of the
formal parameters to the function;

@item
a description of each formal parameter in the C interface; 

@item
a list of possible error conditions; and 

@item
an example of a Fortran 90 program fragment calling the netCDF
function (and perhaps other netCDF functions).
@end itemize

The examples follow a simple convention for error handling, always
checking the error status returned from each netCDF function call and
calling a handle_error function in case an error was detected. For an
example of such a function, see Section 5.2 "Get error message
corresponding to error status: nf90_strerror".

@node NF90_STRERROR, NF90_INQ_LIBVERS, NetCDF Library Interface Descriptions, Datasets
@section NF90_STRERROR
@findex NF90_STRERROR
@cindex NF90_STRERROR, example

The function NF90_STRERROR returns a static reference to an error
message string corresponding to an integer netCDF error status or to a
system error number, presumably returned by a previous call to some
other netCDF function. The list of netCDF error status codes is
available in the appropriate include file for each language binding.

@heading Usage
@example
 function nf90_strerror(ncerr)
   integer, intent( in) :: ncerr
   character(len = 80)  :: nf90_strerror
@end example

@table @code
@item NCERR
An error status that might have been returned from a previous call to
some netCDF function.
@end table

@heading Errors 

If you provide an invalid integer error status that does not
correspond to any netCDF error message or or to any system error
message (as understood by the system strerror function), NF90_STRERROR
returns a string indicating that there is no such error status.

@heading Example 

Here is an example of a simple error handling function that uses
NF90_STRERROR to print the error message corresponding to the netCDF
error status returned from any netCDF function call and then exit:

@example
 subroutine handle_err(status)
   integer, intent ( in) :: status
   
   if(status /= nf90_noerr) then
     print *, trim(nf90_strerror(status))
     stop "Stopped"
   end if
 end subroutine handle_err
@end example

@node NF90_INQ_LIBVERS, NF90_CREATE, NF90_STRERROR, Datasets
@section Get netCDF library version: NF90_INQ_LIBVERS
@findex NF90_INQ_LIBVERS
@cindex NF90_INQ_LIBVERS, example

The function NF90_INQ_LIBVERS returns a string identifying the version
of the netCDF library, and when it was built.

@heading Usage 
@example
 function nf90_inq_libvers()
   character(len = 80) :: nf90_inq_libvers
@end example

@heading Errors 

This function takes no arguments, and returns no error status. 

@heading Example 

Here is an example using nf90_inq_libvers to print the version of the
netCDF library with which the program is linked:

@example
 print *, trim(nf90_inq_libvers())
@end example

@node NF90_CREATE, NF90_OPEN, NF90_INQ_LIBVERS, Datasets
@section NF90_CREATE 
@findex NF90_CREATE 
@cindex NF90_CREATE , example

This function creates a new netCDF dataset, returning a netCDF ID that
can subsequently be used to refer to the netCDF dataset in other
netCDF function calls. The new netCDF dataset opened for write access
and placed in define mode, ready for you to add dimensions, variables,
and attributes.

A creation mode flag specifies whether to overwrite any existing
dataset with the same name and whether access to the dataset is
shared.

@heading Usage 

@example
  function nf90_create(path, cmode, ncid, initialsize, bufrsize, cache_size, &
       cache_nelems, cache_preemption, comm, info)
    implicit none
    character (len = *), intent(in) :: path
    integer, intent(in) :: cmode
    integer, intent(out) :: ncid
    integer, optional, intent(in) :: initialsize
    integer, optional, intent(inout) :: bufrsize
    integer, optional, intent(in) :: cache_size, cache_nelems
    real, optional, intent(in) :: cache_preemption
    integer, optional, intent(in) :: comm, info
    integer :: nf90_create
@end example

@table @code
@item path
The file name of the new netCDF dataset.
 
@item cmode
The creation mode flag. The following flags are available:
NF90_NOCLOBBER, NF90_SHARE, NF90_64BIT_OFFSET, NF90_HDF5, and
NF90_CLASSIC_MODEL.

A zero value (defined for convenience as NF90_CLOBBER) specifies the
default behavior: overwrite any existing dataset with the same file
name and buffer and cache accesses for efficiency. The dataset will be
in netCDF classic format. @xref{NetCDF Classic Format Limitations,,,
netcdf, NetCDF Users' Guide}.

Setting NF90_NOCLOBBER means you do not want to clobber (overwrite) an
existing dataset; an error (NF90_EEXIST) is returned if the specified
dataset already exists.

The NF90_SHARE flag is appropriate when one process may be writing the
dataset and one or more other processes reading the dataset
concurrently; it means that dataset accesses are not buffered and
caching is limited. Since the buffering scheme is optimized for
sequential access, programs that do not access data sequentially may
see some performance improvement by setting the NF90_SHARE flag. (This
only applies to netCDF-3 classic or 64-bit offset files.)

Setting NF90_64BIT_OFFSET causes netCDF to create a 64-bit offset format
file, instead of a netCDF classic format file. The 64-bit offset
format imposes far fewer restrictions on very large (i.e. over 2 GB)
data files. @xref{Large File Support,,, netcdf, NetCDF Users' Guide}.

Setting the NF90_HDF5 flag causes netCDF to create a netCDF-4/HDF5
format output file.

Oring the NF90_CLASSIC_MODEL flag with the NF90_HDF5 flag causes the
resulting netCDF-4/HDF5 file to restrict itself to the classic model -
none of the new netCDF-4 data model features, such as groups or
user-defined types, are allowed in such a file.

@item ncid
Returned netCDF ID.
@end table

The following optional arguments allow additional performance tuning.

@table @code

@item initialsize
The initial size of the file (in bytes) at creation time. A value of 0
causes the file size to be computed when nf90_enddef is called. This
is ignored for NetCDF-4/HDF5 files.

@item bufrsize
Controls a space versus time trade-off, memory allocated in the netcdf
library versus number of system calls. Because of internal
requirements, the value may not be set to exactly the value
requested. The actual value chosen is returned.

The library chooses a system-dependent default value if
NF90_SIZEHINT_DEFAULT is supplied as input. If the "preferred I/O
block size" is available from the stat() system call as member
st_blksize this value is used. Lacking that, twice the system pagesize
is used. Lacking a call to discover the system pagesize, the default
bufrsize is set to 8192 bytes.

The bufrsize is a property of a given open netcdf descriptor ncid, it
is not a persistent property of the netcdf dataset. 

This is ignored for NetCDF-4/HDF5 files.

@item cache_size
If the cache_size is provided when creating a netCDF-4/HDF5 file, it
will be used instead of the default (32000000) as the size, in bytes,
of the HDF5 chunk cache.

@item cache_nelems
If cache_nelems is provided when creating a netCDF-4/HDF5 file, it
will be used instead of the default (1000) as the maximum number of
elements in the HDF5 chunk cache.

@item cache_premtion
If cache_preemption is provided when creating a netCDF-4/HDF5 file, it
will be used instead of the default (0.75) as the preemption value for
the HDF5 chunk cache.

@item comm
If the comm and info parameters are provided the file is created and
opened for parallel I/O. Set the comm parameter to the MPI
communicator (of type MPI_Comm). If this parameter is provided the
info parameter must also be provided.

@item info
If the comm and info parameters are provided the file is created and
opened for parallel I/O. Set the comm parameter to the MPI information
value (of type MPI_Info). If this parameter is provided the comm
parameter must also be provided.

@end table

@heading Errors 
NF90_CREATE returns the value NF90_NOERR if no errors occurred. Possible
causes of errors include:
@itemize

@item
Passing a dataset name that includes a directory that does not exist.
@item
Specifying a dataset name of a file that exists and also specifying
NF90_NOCLOBBER.
@item
Specifying a meaningless value for the creation mode.
@item
Attempting to create a netCDF dataset in a directory where you don't
have permission to create files.
@end itemize

@heading Example 

In this example we create a netCDF dataset named foo.nc; we want the
dataset to be created in the current directory only if a dataset with
that name does not already exist:

@example
 use netcdf
 implicit none
 integer :: ncid, status
 ...
 status = nf90_create(path = "foo.nc", cmode = nf90_noclobber, ncid = ncid)
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_OPEN, NF90_REDEF, NF90_CREATE, Datasets
@section NF90_OPEN 
@findex NF90_OPEN 
@cindex NF90_OPEN , example

The function NF90_OPEN opens an existing netCDF dataset for access.

@heading Usage 

@example
  function nf90_open(path, mode, ncid, bufrsize, cache_size, cache_nelems, &
                     cache_preemption, comm, info)
    implicit none
    character (len = *), intent(in) :: path
    integer, intent(in) :: mode
    integer, intent(out) :: ncid
    integer, optional, intent(inout) :: bufrsize
    integer, optional, intent(in) :: cache_size, cache_nelems
    real, optional, intent(in) :: cache_preemption
    integer, optional, intent(in) :: comm, info
    integer :: nf90_open
@end example

@table @code

@item path
File name for netCDF dataset to be opened.
This may be an OPeNDAP URL if DAP support is enabled.
 
@item mode
A zero value (or NF90_NOWRITE) specifies the default behavior: open the
dataset with read-only access, buffering and caching accesses for
efficiency

Otherwise, the open mode is NF90_WRITE, NF90_SHARE, or
NF90_WRITE|NF90_SHARE. Setting the NF90_WRITE flag opens the dataset
with read-write access. ("Writing" means any kind of change to the
dataset, including appending or changing data, adding or renaming
dimensions, variables, and attributes, or deleting attributes.) The
NF90_SHARE flag is appropriate when one process may be writing the
dataset and one or more other processes reading the dataset
concurrently (note that this is not the same as parallel I/O); it
means that dataset accesses are not buffered and caching is
limited. Since the buffering scheme is optimized for sequential
access, programs that do not access data sequentially may see some
performance improvement by setting the NF90_SHARE flag.
 
@item ncid
Returned netCDF ID.
@end table

The following optional argument allows additional performance tuning.

@table @code

@item bufrsize
This parameter applies only when opening classic format or 64-bit
offset files. It is ignored for netCDF-4/HDF5 files. 

It Controls a space versus time trade-off, memory allocated in the netcdf
library versus number of system calls. Because of internal
requirements, the value may not be set to exactly the value
requested. The actual value chosen is returned.

The library chooses a system-dependent default value if
NF90_SIZEHINT_DEFAULT is supplied as input. If the "preferred I/O
block size" is available from the stat() system call as member
st_blksize this value is used. Lacking that, twice the system pagesize
is used. Lacking a call to discover the system pagesize, the default
bufrsize is set to 8192 bytes.

The bufrsize is a property of a given open netcdf descriptor ncid, it
is not a persistent property of the netcdf dataset.

@item cache_size
If the cache_size is provided when opening a netCDF-4/HDF5 file, it
will be used instead of the default (32000000) as the size, in bytes,
of the HDF5 chunk cache.

@item cache_nelems
If cache_nelems is provided when opening a netCDF-4/HDF5 file, it
will be used instead of the default (1000) as the maximum number of
elements in the HDF5 chunk cache.

@item cache_premtion
If cache_preemption is provided when opening a netCDF-4/HDF5 file, it
will be used instead of the default (0.75) as the preemption value
for the HDF5 chunk cache.

@item comm
If the comm and info parameters are provided the file is opened for
parallel I/O. Set the comm parameter to the MPI communicator (of type
MPI_Comm). If this parameter is provided the info parameter must also
be provided.

@item info
If the comm and info parameters are provided the file is opened for
parallel I/O. Set the comm parameter to the MPI information value (of
type MPI_Info). If this parameter is provided the comm parameter must
also be provided.

@end table

@heading Errors 

NF90_OPEN returns the value NF90_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
The specified netCDF dataset does not exist. 
@item
A meaningless mode was specified. 
@end itemize

@heading Example 
Here is an example using NF90_OPEN to open an existing netCDF dataset
named foo.nc for read-only, non-shared access:

@example
 use netcdf
 implicit none
 integer :: ncid, status
 ...
 status = nf90_open(path = "foo.nc", mode = nf90_nowrite, ncid = ncid)
 if (status /= nf90_noerr) call handle_err(status)
@end example

@heading Example 
Here is an example using NF90_OPEN to open an existing netCDF dataset
for parallel I/O access. (Note the use of the comm and info
parameters). This example is from test program
nf_test/f90tst_parallel.f90.

@example
 use netcdf
 implicit none
 integer :: ncid, status
 ...
  ! Reopen the file.
  call handle_err(nf90_open(FILE_NAME, nf90_nowrite, ncid, comm = MPI_COMM_WORLD, &
       info = MPI_INFO_NULL))
@end example

@node NF90_REDEF, NF90_ENDDEF, NF90_OPEN, Datasets
@section NF90_REDEF 
@findex NF90_REDEF 
@cindex NF90_REDEF , example

The function NF90_REDEF puts an open netCDF dataset into define mode, so
dimensions, variables, and attributes can be added or renamed and
attributes can be deleted.

@heading Usage 

@example
 function nf90_redef(ncid)
   integer, intent( in) :: ncid
   integer              :: nf90_redef
@end example

@table @code
@item ncid
netCDF ID, from a previous call to NF90_OPEN or NF90_CREATE.
@end table

@heading Errors 
NF90_REDEF returns the value NF90_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
The specified netCDF dataset is already in define mode. 

@item
The specified netCDF dataset was opened for read-only. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example 
Here is an example using NF90_REDEF to open an existing netCDF dataset
named foo.nc and put it into define mode:

@example
 use netcdf
 implicit none
 integer :: ncid, status
 ...
 status = nf90_open("foo.nc", nf90_write, ncid) ! Open dataset
 if (status /= nf90_noerr) call handle_err(status)
 ...
 status = nf90_redef(ncid)                       ! Put the file in define mode
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_ENDDEF, NF90_CLOSE, NF90_REDEF, Datasets
@section NF90_ENDDEF 
@findex NF90_ENDDEF 
@cindex NF90_ENDDEF , example

The function NF90_ENDDEF takes an open netCDF dataset out of define
mode. The changes made to the netCDF dataset while it was in define
mode are checked and committed to disk if no problems
occurred. Non-record variables may be initialized to a "fill value" as
well (@pxref{NF90_SET_FILL}). The netCDF dataset is then placed in
data mode, so variable data can be read or written.

This call may involve copying data under some circumstances. For a
more extensive discussion @xref{File Structure and
Performance,,,netcdf, NetCDF Users Guide}.

@heading Usage 

@example
 function nf90_enddef(ncid, h_minfree, v_align, v_minfree, r_align)
   integer,           intent( in) :: ncid
   integer, optional, intent( in) :: h_minfree, v_align, v_minfree, r_align
   integer                        :: nf90_enddef
@end example

@table @code
@item ncid
NetCDF ID, from a previous call to NF90_OPEN or NF90_CREATE.
@end table

The following arguments allow additional performance tuning. Note:
these arguments expose internals of the netcdf version 1 file format,
and may not be available in future netcdf implementations.

The current netcdf file format has three sections: the "header"
section, the data section for fixed size variables, and the data
section for variables which have an unlimited dimension (record
variables). The header begins at the beginning of the file. The index
(offset) of the beginning of the other two sections is contained in
the header. Typically, there is no space between the sections. This
causes copying overhead to accrue if one wishes to change the size of
the sections, as may happen when changing the names of things, text
attribute values, adding attributes or adding variables. Also, for
buffered i/o, there may be advantages to aligning sections in certain
ways.

The minfree parameters allow one to control costs of future calls to
nf90_redef or nf90_enddef by requesting that some space be available
at the end of the section. The default value for both h_minfree and
v_minfree is 0.

The align parameters allow one to set the alignment of the beginning
of the corresponding sections. The beginning of the section is rounded
up to an index which is a multiple of the align parameter. The flag
value NF90_ALIGN_CHUNK tells the library to use the bufrsize (see
above) as the align parameter. The default value for both v_align and
r_align is 4 bytes.

@table @code

@item h_minfree
Size of the pad (in bytes) at the end of the "header" section.

@item v_minfree
Size of the pad (in bytes) at the end of the data section for fixed
size variables.

@item v_align
The alignment of the beginning of the data section for fixed size
variables.

@item r_align
The alignment of the beginning of the data section for variables which
have an unlimited dimension (record variables). 

@end table

@heading Errors 

NF90_ENDDEF returns the value NF90_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
The specified netCDF dataset is not in define mode. 

@item
The specified netCDF ID does not refer to an open netCDF dataset.

@item
The size of one or more variables exceed the size constraints for
whichever variant of the file format is in use).
@xref{Large File Support,,, netcdf, @value{n-man}}.
@end itemize

@heading Example 

Here is an example using NF90_ENDDEF to finish the definitions of a new
netCDF dataset named foo.nc and put it into data mode:

@example
 use netcdf
 implicit none
 integer :: ncid, status
 ...
 status = nf90_create("foo.nc", nf90_noclobber, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  !  create dimensions, variables, attributes
 status = nf90_enddef(ncid) 
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_CLOSE, NF90_INQUIRE Family, NF90_ENDDEF, Datasets
@section NF90_CLOSE 
@findex NF90_CLOSE 
@cindex NF90_CLOSE , example

The function NF90_CLOSE closes an open netCDF dataset. If the dataset is
in define mode, NF90_ENDDEF will be called before closing. (In this
case, if NF90_ENDDEF returns an error, NF90_ABORT will automatically be
called to restore the dataset to the consistent state before define
mode was last entered.) After an open netCDF dataset is closed, its
netCDF ID may be reassigned to the next netCDF dataset that is opened
or created.

@heading Usage 
@example
 function nf90_close(ncid)
   integer, intent( in) :: ncid
   integer              :: nf90_close
@end example

@table @code
@item ncid
NetCDF ID, from a previous call to NF90_OPEN or NF90_CREATE.
@end table

@heading Errors 

NF90_CLOSE returns the value NF90_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
Define mode was entered and the automatic call made to NF90_ENDDEF
failed.

@item
The specified netCDF ID does not refer to an open netCDF dataset.
@end itemize

@heading Example 

Here is an example using NF90_CLOSE to finish the definitions of a new
netCDF dataset named foo.nc and release its netCDF ID:

@example
 use netcdf
 implicit none
 integer :: ncid, status
 ...
 status = nf90_create("foo.nc", nf90_noclobber, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  !  create dimensions, variables, attributes
 status = nf90_close(ncid) 
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_INQUIRE Family, NF90_SYNC, NF90_CLOSE, Datasets
@section NF90_INQUIRE Family

The NF90_INQUIRE subroutine returns information about an open netCDF
dataset, given its netCDF ID. The subroutine can be called from either
define mode or data mode, and returns values for any or all of the
following: the number of dimensions, the number of variables, the
number of global attributes, and the dimension ID of the dimension
defined with unlimited length, if any.    An additional function,
NF90_INQ_FORMAT, returns the (rarely needed) format version.

No I/O is performed when NF90_INQUIRE is called, since the required
information is available in memory for each open netCDF dataset.

@heading Usage 
@example
 function nf90_inquire(ncid, nDimensions, nVariables, nAttributes, &
                       unlimitedDimId, formatNum)
   integer,           intent( in) :: ncid
   integer, optional, intent(out) :: nDimensions, nVariables, &
                                     nAttributes, unlimitedDimId, &
                                     formatNum
   integer                        :: nf90_inquire
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item nDimensions
Returned number of dimensions defined for this netCDF dataset.
 
@item nVariables
Returned number of variables defined for this netCDF dataset.
 
@item nAttributes
Returned number of global attributes defined for this netCDF dataset.
 
@item unlimitedDimID
Returned ID of the unlimited dimension, if there is one for this
netCDF dataset. If no unlimited length dimension has been defined, -1
is returned.

@item format
Returned integer indicating format version for this dataset, one of
nf90_format_classic,
nf90_format_64bit,
nf90_format_netcdf4, or
nf90_format_netcdf4_classic.  These are rarely needed by users or
applications, since thhe library recognizes the format of a file it is
accessing and handles it accordingly.
@end table

@heading Errors 

Function NF90_INQUIRE returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example 

Here is an example using NF90_INQUIRE to find out about a netCDF dataset
named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid, status, nDims, nVars, nGlobalAtts, unlimDimID
 ...
 status = nf90_open("foo.nc", nf90_nowrite, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 status = nf90_inquire(ncid, nDims, nVars, nGlobalAtts, unlimdimid) 
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_inquire(ncid, nDimensions = nDims, &
                       unlimitedDimID = unlimdimid) 
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_SYNC, NF90_ABORT, NF90_INQUIRE Family, Datasets
@section NF90_SYNC 
@findex NF90_SYNC 
@cindex NF90_SYNC , example

The function NF90_SYNC offers a way to synchronize the disk copy of a
netCDF dataset with in-memory buffers. There are two reasons you might
want to synchronize after writes:
@itemize

@item
To minimize data loss in case of abnormal termination, or 

@item
To make data available to other processes for reading immediately
after it is written. But note that a process that already had the
dataset open for reading would not see the number of records increase
when the writing process calls NF90_SYNC; to accomplish this, the
reading process must call NF90_SYNC.
@end itemize

This function is backward-compatible with previous versions of the
netCDF library. The intent was to allow sharing of a netCDF dataset
among multiple readers and one writer, by having the writer call
NF90_SYNC after writing and the readers call NF90_SYNC before each
read. For a writer, this flushes buffers to disk. For a reader, it
makes sure that the next read will be from disk rather than from
previously cached buffers, so that the reader will see changes made by
the writing process (e.g., the number of records written) without
having to close and reopen the dataset. If you are only accessing a
small amount of data, it can be expensive in computer resources to
always synchronize to disk after every write, since you are giving up
the benefits of buffering.

An easier way to accomplish sharing (and what is now recommended) is
to have the writer and readers open the dataset with the NF90_SHARE
flag, and then it will not be necessary to call NF90_SYNC at
all. However, the NF90_SYNC function still provides finer granularity
than the NF90_SHARE flag, if only a few netCDF accesses need to be
synchronized among processes.

It is important to note that changes to the ancillary data, such as
attribute values, are not propagated automatically by use of the
NF90_SHARE flag. Use of the NF90_SYNC function is still required for
this purpose.

Sharing datasets when the writer enters define mode to change the data
schema requires extra care. In previous releases, after the writer
left define mode, the readers were left looking at an old copy of the
dataset, since the changes were made to a new copy. The only way
readers could see the changes was by closing and reopening the
dataset. Now the changes are made in place, but readers have no
knowledge that their internal tables are now inconsistent with the new
dataset schema. If netCDF datasets are shared across redefinition,
some mechanism external to the netCDF library must be provided that
prevents access by readers during redefinition and causes the readers
to call NF90_SYNC before any subsequent access.

When calling NF90_SYNC, the netCDF dataset must be in data mode. A
netCDF dataset in define mode is synchronized to disk only when
NF90_ENDDEF is called. A process that is reading a netCDF dataset that
another process is writing may call NF90_SYNC to get updated with the
changes made to the data by the writing process (e.g., the number of
records written), without having to close and reopen the dataset.

Data is automatically synchronized to disk when a netCDF dataset is
closed, or whenever you leave define mode.

@heading Usage 
@example
 function nf90_sync(ncid)
   integer, intent( in) :: ncid
   integer              :: nf90_sync
@end example

@table @code
@item ncid
NetCDF ID, from a previous call to NF90_OPEN or NF90_CREATE.
@end table

@heading Errors 

NF90_SYNC returns the value NF90_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
The netCDF dataset is in define mode. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example 

Here is an example using NF90_SYNC to synchronize the disk writes of a
netCDF dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid, status
 ...
 status = nf90_open("foo.nc", nf90_write, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 ! write data or change attributes
 ...  
 status = NF90_SYNC(ncid) 
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_ABORT, NF90_SET_FILL, NF90_SYNC, Datasets
@section NF90_ABORT 
@findex NF90_ABORT 
@cindex NF90_ABORT , example

You no longer need to call this function, since it is called
automatically by NF90_CLOSE in case the dataset is in define mode and
something goes wrong with committing the changes. The function
NF90_ABORT just closes the netCDF dataset, if not in define mode. If the
dataset is being created and is still in define mode, the dataset is
deleted. If define mode was entered by a call to NF90_REDEF, the netCDF
dataset is restored to its state before definition mode was entered
and the dataset is closed.

@heading Usage 
@example
 function nf90_abort(ncid)
   integer, intent( in) :: ncid
   integer              :: nf90_abort
@end example

@table @code
@item ncid
NetCDF ID, from a previous call to NF90_OPEN or NF90_CREATE.
@end table

@heading Errors 

NF90_ABORT returns the value NF90_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
When called from define mode while creating a netCDF dataset, deletion
of the dataset failed.

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example 

Here is an example using NF90_ABORT to back out of redefinitions of a
dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid, status, LatDimID
 ...
 status = nf90_open("foo.nc", nf90_write, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 status = nf90_redef(ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 status = nf90_def_dim(ncid, "Lat", 18, LatDimID) 
 if (status /= nf90_noerr) then ! Dimension definition failed
   call handle_err(status)
   status = nf90_abort(ncid) ! Abort redefinitions
   if (status /= nf90_noerr) call handle_err(status)
 end if
...
@end example

@node NF90_SET_FILL,  , NF90_ABORT, Datasets
@section NF90_SET_FILL 
@findex NF90_SET_FILL 
@cindex NF90_SET_FILL , example

This function is intended for advanced usage, to optimize writes under
some circumstances described below. The function NF90_SET_FILL sets
the fill mode for a netCDF dataset open for writing and returns the
current fill mode in a return parameter. The fill mode can be
specified as either NF90_FILL or NF90_NOFILL. The default behavior
corresponding to NF90_FILL is that data is pre-filled with fill
values, that is fill values are written when you create non-record
variables or when you write a value beyond data that has not yet been
written. This makes it possible to detect attempts to read data before
it was written. @xref{Fill Values}, for more information on the use of
fill values. @xref{Attribute Conventions,,,netcdf, @value{n-man}}, for
information about how to define your own fill values.

The behavior corresponding to NF90_NOFILL overrides the default behavior
of prefilling data with fill values. This may enhance
performance, because it avoids the duplicate writes that occur when
the netCDF library writes fill values that are later overwritten with
data, at the cost of losing the ability to later detect access of
values that were never written.

A value indicating which mode the netCDF dataset was already in is
returned. You can use this value to temporarily change the fill mode
of an open netCDF dataset and then restore it to the previous mode.

After you turn on NF90_NOFILL mode for an open netCDF dataset, you must
be certain to write valid data in all the positions that will later be
read. Note that nofill mode is only a transient property of a netCDF
dataset open for writing: if you close and reopen the dataset, it will
revert to the default behavior. You can also revert to the default
behavior by calling NF90_SET_FILL again to explicitly set the fill mode
to NF90_FILL.

There are three situations where it might be advantageous to set nofill
mode:
@enumerate
@item
Creating and initializing a netCDF dataset. In this case, you could
set nofill mode before calling NF90_ENDDEF and then write completely all
non-record variables and the initial records of all the record
variables you want to initialize.
@item
Extending an existing record-oriented netCDF dataset. Set nofill mode
after opening the dataset for writing, then append the additional
records to the dataset completely, leaving no intervening unwritten
records.
@item
Adding new variables that you are going to initialize to an existing
netCDF dataset. Set nofill mode before calling NF90_ENDDEF then write
all the new variables completely.
@end enumerate

If the netCDF dataset has an unlimited dimension and the last record
was written while in nofill mode, then the dataset may be shorter than
if nofill mode was not set, but this will be completely transparent if
you access the data only through the netCDF interfaces.

The use of this feature may not be available (or even needed) in
future releases. Programmers are cautioned against heavy reliance upon
this feature.

@heading Usage 
@example
 function nf90_set_fill(ncid, fillmode, old_mode)
   integer, intent( in) :: ncid, fillmode 
   integer, intent(out) :: old_mode
   integer              :: nf90_set_fill
@end example

@table @code
@item ncid
NetCDF ID, from a previous call to NF90_OPEN or NF90_CREATE.
 
@item fillmode
Desired fill mode for the dataset, either NF90_NOFILL or NF90_FILL.
 
@item old_mode
Returned current fill mode of the dataset before this call, either
NF90_NOFILL or NF90_FILL.
@end table

@heading Errors 

NF90_SET_FILL returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:
@itemize

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@item
The specified netCDF ID refers to a dataset open for read-only access. 

@item
The fill mode argument is neither NF90_NOFILL nor NF90_FILL.. 
@end itemize

@heading Example 

Here is an example using NF90_SET_FILL to set nofill mode for subsequent
writes of a netCDF dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid, status, oldMode
 ...
 status = nf90_open("foo.nc", nf90_write, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 ! Write data with prefilling behavior
 ...  
 status = nf90_set_fill(ncid, nf90_nofill, oldMode) 
 if (status /= nf90_noerr) call handle_err(status)
 ...
 !  Write data with no prefilling
 ...
@end example

@node Groups, Dimensions, Datasets, Top
@chapter Groups
@cindex groups, overview

NetCDF-4 added support for hierarchical groups within netCDF
datasets. 

Groups are identified with a ncid, which identifies both the open
file, and the group within that file. When a file is opened with
NF90_OPEN or NF90_CREATE, the ncid for the root group of that file is
provided. Using that as a starting point, users can add new groups, or
list and navigate existing groups.

All netCDF calls take a ncid which determines where the call will
take its action. For example, the NF90_DEF_VAR function takes a ncid as
its first parameter. It will create a variable in whichever group
its ncid refers to. Use the root ncid provided by NF90_CREATE or
NF90_OPEN to create a variable in the root group. Or use NF90_DEF_GRP to
create a group and use its ncid to define a variable in the new
group.

Variable are only visible in the group in which they are defined. The
same applies to attributes. ``Global'' attributes are defined in
whichever group is referred to by the ncid. 

Dimensions are visible in their groups, and all child groups.

Group operations are only permitted on netCDF-4 files - that is, files
created with the HDF5 flag in nf90_create. (@pxref{NF90_CREATE}). Groups
are not compatible with the netCDF classic data model, so files
created with the NF90_CLASSIC_MODEL file cannot contain groups (except
the root group).

@menu
* NF90_INQ_NCID::               
* NF90_INQ_GRPS::               
* NF90_INQ_VARIDS::             
* NF90_INQ_DIMIDS::             
* NF90_INQ_GRPNAME_LEN::        
* NF90_INQ_GRPNAME::            
* NF90_INQ_GRPNAME_FULL::       
* NF90_INQ_GRP_PARENT::         
* NF90_INQ_GRP_NCID::           
* NF90_INQ_GRP_FULL_NCID::      
* NF90_DEF_GRP::                
@end menu

@node NF90_INQ_NCID, NF90_INQ_GRPS, Groups, Groups
@section Find a Group ID: NF90_INQ_NCID
@findex NF90_INQ_NCID

Given an ncid and group name (NULL or "" gets root group), return
ncid of the named group.

@heading Usage 

@example
  function nf90_inq_ncid(ncid, name, grp_ncid)
    integer, intent(in) :: ncid
    character (len = *), intent(in) :: name
    integer, intent(out) :: grp_ncid
    integer :: nf90_inq_ncid
@end example

@table @code

@item NCID
The group id for this operation.

@item NAME
A character array that holds the name of the desired group. Must be
less then NF90_MAX_NAME.

@item GRPID
The ID of the group will go here.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This example is from nf90_test/ftst_groups.F.

@example
@end example

@node NF90_INQ_GRPS, NF90_INQ_VARIDS, NF90_INQ_NCID, Groups
@section Get a List of Groups in a Group: NF90_INQ_GRPS
@findex NF90_INQ_GRPS

Given a location id, return the number of groups it contains, and an
array of their ncids.

@heading Usage 

@example
  function nf90_inq_grps(ncid, numgrps, ncids)
    integer, intent(in) :: ncid
    integer, intent(out) :: numgrps
    integer, intent(out) :: ncids
    integer :: nf90_inq_grps
@end example

@table @code

@item NCID
The group id for this operation.

@item NUMGRPS
An integer which will get number of groups in this group. 

@item NCIDS
An array of ints which will receive the IDs of all the groups in this
group.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example


@example
@end example

@node NF90_INQ_VARIDS, NF90_INQ_DIMIDS, NF90_INQ_GRPS, Groups
@section Find all the Variables in a Group: NF90_INQ_VARIDS
@findex NF90_INQ_VARIDS

Find all varids for a location.

@heading Usage 

@example
  function nf90_inq_varids(ncid, nvars, varids)
    integer, intent(in) :: ncid
    integer, intent(out) :: nvars
    integer, intent(out) :: varids
    integer :: nf90_inq_varids
@end example

@table @code

@item NCID
The group id for this operation.

@item VARIDS
An already allocated array to store the list of varids. Use
nf90_inq_nvars to find out how many variables there
are. (@pxref{NF90_INQUIRE_VARIABLE}).

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example


@example
@end example

@node NF90_INQ_DIMIDS, NF90_INQ_GRPNAME_LEN, NF90_INQ_VARIDS, Groups
@section Find all Dimensions Visible in a Group: NF90_INQ_DIMIDS
@findex NF90_INQ_DIMIDS

Find all dimids for a location. This finds all dimensions in a group,
or any of its parents.

@heading Usage 

@example
  function nf90_inq_dimids(ncid, ndims, dimids, include_parents)
    integer, intent(in) :: ncid
    integer, intent(out) :: ndims
    integer, intent(out) :: dimids
    integer, intent(out) :: include_parents
    integer :: nf90_inq_dimids
@end example

@table @code

@item NCID
The group id for this operation.

@item NDIMS
Returned number of dimensions for this location.  If include_parents
is non-zero, number of dimensions visible from this group, which
includes dimensions in parent groups.

@item DIMIDS
An array of ints when the dimids of the visible dimensions will be
stashed. Use nf90_inq_ndims to find out how many dims are visible from
this group. (@pxref{NF90_INQUIRE_VARIABLE}).

@item INCLUDE_PARENTS
If zero, only the group specified by NCID will be searched for
dimensions. Otherwise parent groups will be searched too.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example


@example
@end example

@node NF90_INQ_GRPNAME_LEN, NF90_INQ_GRPNAME, NF90_INQ_DIMIDS, Groups
@section Find the Length of a Group's Full Name: NF90_INQ_GRPNAME_LEN
@findex NF90_INQ_GRPNAME_LEN

Given ncid, find length of the full name. (Root group is named "/",
with length 1.)

@heading Usage 

@example
  function nf90_inq_grpname_len(ncid, len)
    integer, intent(in) :: ncid
    integer, intent(out) :: len
    integer :: nf90_inq_grpname_len
  end function nf90_inq_grpname_len
@end example

@table @code

@item NCID
The group id for this operation.

@item LEN
An integer where the length will be placed.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
@end example

@node NF90_INQ_GRPNAME, NF90_INQ_GRPNAME_FULL, NF90_INQ_GRPNAME_LEN, Groups
@section Find a Group's Name: NF90_INQ_GRPNAME
@findex NF90_INQ_GRPNAME

Given ncid, find relative name of group. (Root group is named "/").

The name provided by this function is relative to the parent
group. For a full path name for the group is, with all parent groups
included, separated with a forward slash (as in Unix directory names) @xref{NF90_INQ_GRPNAME_FULL}.

@heading Usage 

@example
  function nf90_inq_grpname(ncid, name)
    integer, intent(in) :: ncid
    character (len = *), intent(out) :: name
    integer :: nf90_inq_grpname
@end example

@table @code

@item NCID
The group id for this operation.

@item NAME
The name of the
group will be copied to this character array. The name will be less
than NF90_MAX_NAME in length.
@item

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example


@example
@end example

@node NF90_INQ_GRPNAME_FULL, NF90_INQ_GRP_PARENT, NF90_INQ_GRPNAME, Groups
@section Find a Group's Full Name: NF90_INQ_GRPNAME_FULL
@findex NF90_INQ_GRPNAME_FULL

Given ncid, find complete name of group. (Root group is named "/").

The name provided by this function is a full path name for the group
is, with all parent groups included, separated with a forward slash
(as in Unix directory names). For a name relative to the parent group
@xref{NF90_INQ_GRPNAME}.

To find the length of the full name @xref{NF90_INQ_GRPNAME_LEN}.

@heading Usage 

@example
  function nf90_inq_grpname_full(ncid, len, name)
    integer, intent(in) :: ncid
    integer, intent(out) :: len
    character (len = *), intent(out) :: name
    integer :: nf90_inq_grpname_full
@end example

@table @code

@item NCID
The group id for this operation.

@item LEN
The length of the full group name will go here.      

@item NAME
The name of the group will be copied to this character array. 

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example
This example is from test program nf_test/f90tst_grps.f90.         

@example
  call check(nf90_inq_grpname_full(grpid1, len, name_in))
  if (name_in .ne. grp1_full_name) stop 62
@end example

@node NF90_INQ_GRP_PARENT, NF90_INQ_GRP_NCID, NF90_INQ_GRPNAME_FULL, Groups
@section Find a Group's Parent: NF90_INQ_GRP_PARENT
@findex NF90_INQ_GRP_PARENT

Given ncid, find the ncid of the parent group. 

When used with the root group, this function returns the NF90_ENOGRP
error (since the root group has no parent.)

@heading Usage 

@example
  function nf90_inq_grp_parent(ncid, parent_ncid)
    integer, intent(in) :: ncid
    integer, intent(out) :: parent_ncid
    integer :: nf90_inq_grp_parent
@end example

@table @code

@item NCID
The group id.

@item PARENT_NCID
The ncid of the parent group will be copied here.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENOGRP
No parent group found (i.e. this is the root group).

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
@end example

@node NF90_INQ_GRP_NCID, NF90_INQ_GRP_FULL_NCID, NF90_INQ_GRP_PARENT, Groups
@section Find a Group by Name: NF90_INQ_GRP_NCID
@findex NF90_INQ_GRP_PARENT

Given a group name and an ncid, find the ncid of the group id. 

@heading Usage 

@example
  function nf90_inq_grp_ncid(ncid, name, grpid)
    integer, intent(in) :: ncid
    character (len = *), intent(in) :: name
    integer, intent(out) :: grpid
    integer :: nf90_inq_grp_ncid
  
    nf90_inq_grp_ncid = nf_inq_grp_ncid(ncid, name, grpid)
  end function nf90_inq_grp_ncid
@end example

@table @code

@item NCID
The group id to look in.

@item GRP_NAME
The name of the group that should be found.

@item GRP_NCID
This will get the group id, if it is found.

@end table

@heading Return Codes

The following return codes may be returned by this function.

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_EINVAL
No name provided or name longer than NF90_MAX_NAME.

@item NF90_ENOGRP
Named group not found.

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example
This example is from test program nf_test/f90tst_grps.f90.         

@example
  ! Get the group ids for the newly reopened file.
  call check(nf90_inq_grp_ncid(ncid, GRP1_NAME, grpid1))
  call check(nf90_inq_grp_ncid(grpid1, GRP2_NAME, grpid2))
  call check(nf90_inq_grp_ncid(grpid2, GRP3_NAME, grpid3))
  call check(nf90_inq_grp_ncid(grpid3, GRP4_NAME, grpid4))
@end example

@node NF90_INQ_GRP_FULL_NCID, NF90_DEF_GRP, NF90_INQ_GRP_NCID, Groups
@section Find a Group by its Fully-qualified Name: NF90_INQ_GRP_FULL_NCID
@findex NF90_INQ_GRP_PARENT

Given a fully qualified group name and an ncid, find the ncid of the
group id.

@heading Usage 

@example
  function nf90_inq_grpname_full(ncid, len, name)
    integer, intent(in) :: ncid
    integer, intent(out) :: len
    character (len = *), intent(out) :: name
    integer :: nf90_inq_grpname_full
  
    nf90_inq_grpname_full = nf_inq_grpname_full(ncid, len, name)
  end function nf90_inq_grpname_full
@end example

@table @code

@item NCID
The group id to look in.

@item FULL_NAME
The fully-qualified group name.

@item GRP_NCID
This will get the group id, if it is found.

@end table

@heading Return Codes

The following return codes may be returned by this function.

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_EINVAL
No name provided or name longer than NF90_MAX_NAME.

@item NF90_ENOGRP
Named group not found.

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example
This example is from test program nf_test/tstf90_grps.f90.

@example
  ! Check for the groups with full group names. 
  write(grp1_full_name, '(AA)') '/', GRP1_NAME
  call check(nf90_inq_grp_full_ncid(ncid, grp1_full_name, grpid1))
@end example

@node NF90_DEF_GRP,  , NF90_INQ_GRP_FULL_NCID, Groups
@section Create a New Group: NF90_DEF_GRP
@findex NF90_DEF_GRP

Create a group. Its location id is returned in new_ncid. 

@heading Usage 

@example
  function nf90_def_grp(parent_ncid, name, new_ncid)
    integer, intent(in) :: parent_ncid
    character (len = *), intent(in) :: name
    integer, intent(out) :: new_ncid
    integer :: nf90_def_grp
@end example

@table @code

@item PARENT_NCID
The group id of the parent group.

@item NAME
The name of the new group, which must be different from the name of
any variable within the same parent group.

@item NEW_NCID
The ncid of the new group will be placed there.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENAMEINUSE
That name is in use. Group names must be unique within a group.

@item NF90_EMAXNAME
Name exceed max length NF90_MAX_NAME.

@item NF90_EBADNAME
Name contains illegal characters.

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@item NF90_EPERM
Attempt to write to a read-only file.

@item NF90_ENOTINDEFINE
Not in define mode.

@end table

@heading Example

@example
C     Create the netCDF file.
      retval = nf90_create(file_name, NF90_NETCDF4, ncid)
      if (retval .ne. nf90_noerr) call handle_err(retval)

C     Create a group and a subgroup.
      retval = nf90_def_grp(ncid, group_name, grpid)
      if (retval .ne. nf90_noerr) call handle_err(retval)
      retval = nf90_def_grp(grpid, sub_group_name, sub_grpid)
      if (retval .ne. nf90_noerr) call handle_err(retval)
@end example

@node Dimensions, User Defined Data Types, Groups, Top
@chapter Dimensions

@menu
* Dimensions Introduction::     
* NF90_DEF_DIM::                
* NF90_INQ_DIMID::              
* NF90_INQUIRE_DIMENSION::      
* NF90_RENAME_DIM::             
@end menu

@node Dimensions Introduction, NF90_DEF_DIM, Dimensions, Dimensions
@section Dimensions Introduction

Dimensions for a netCDF dataset are defined when it is created, while
the netCDF dataset is in define mode. Additional dimensions may be
added later by reentering define mode. A netCDF dimension has a name
and a length. At most one dimension in a netCDF dataset can have the
unlimited length, which means variables using this dimension can grow
along this dimension.

There is a suggested limit (512) to the number of dimensions that can
be defined in a single netCDF dataset. The limit is the value of the
constant NF90_MAX_DIMS. The purpose of the limit is to make writing
generic applications simpler. They need only provide an array of
NF90_MAX_DIMS dimensions to handle any netCDF dataset. The
implementation of the netCDF library does not enforce this advisory
maximum, so it is possible to use more dimensions, if necessary, but
netCDF utilities that assume the advisory maximums may not be able to
handle the resulting netCDF datasets.

Ordinarily, the name and length of a dimension are fixed when the
dimension is first defined. The name may be changed later, but the
length of a dimension (other than the unlimited dimension) cannot be
changed without copying all the data to a new netCDF dataset with a
redefined dimension length.

A netCDF dimension in an open netCDF dataset is referred to by a small
integer called a dimension ID. In the Fortran 90 interface, dimension
IDs are 1, 2, 3, ..., in the order in which the dimensions were
defined.

Operations supported on dimensions are: 
@itemize

@item
Create a dimension, given its name and length. 

@item
Get a dimension ID from its name. 

@item
Get a dimension's name and length from its ID. 

@item
Rename a dimension. 
@end itemize

@node NF90_DEF_DIM, NF90_INQ_DIMID, Dimensions Introduction, Dimensions
@section NF90_DEF_DIM 
@findex NF90_DEF_DIM
@cindex NF90_DEF_DIM, example

The function NF90_DEF_DIM adds a new dimension to an open netCDF dataset
in define mode. It returns (as an argument) a dimension ID, given the
netCDF ID, the dimension name, and the dimension length. At most one
unlimited length dimension, called the record dimension, may be
defined for each netCDF dataset.

@heading Usage 
@example
 function nf90_def_dim(ncid, name, len, dimid)
   integer,             intent( in) :: ncid
   character (len = *), intent( in) :: name
   integer,             intent( in) :: len
   integer,             intent(out) :: dimid
   integer                          :: nf90_def_dim
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item name
Dimension name.
 
@item len
Length of dimension; that is, number of values for this dimension as
an index to variables that use it. This should be either a positive
integer or the predefined constant NF90_UNLIMITED.
 
@item dimid
Returned dimension ID.
@end table

@heading Errors 

NF90_DEF_DIM returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:
@itemize

@item
The netCDF dataset is not in definition mode. 

@item
The specified dimension name is the name of another existing
dimension.

@item
The specified length is not greater than zero. 

@item
The specified length is unlimited, but there is already an unlimited
length dimension defined for this netCDF dataset.

@item
The specified netCDF ID does not refer to an open netCDF dataset.

@end itemize

@heading Example 

Here is an example using NF90_DEF_DIM to create a dimension named lat of
length 18 and a unlimited dimension named rec in a new netCDF dataset
named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid, status, LatDimID, RecordDimID
 ...
 status = nf90_create("foo.nc", nf90_noclobber, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 status = nf90_def_dim(ncid, "Lat", 18, LatDimID) 
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_def_dim(ncid, "Record", nf90_unlimited, RecordDimID)
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_INQ_DIMID, NF90_INQUIRE_DIMENSION, NF90_DEF_DIM, Dimensions
@section NF90_INQ_DIMID 
@findex NF90_INQ_DIMID 
@cindex NF90_INQ_DIMID , example

The function NF90_INQ_DIMID returns (as an argument) the ID of a netCDF
dimension, given the name of the dimension. If ndims is the number of
dimensions defined for a netCDF dataset, each dimension has an ID
between 1 and ndims.

@heading Usage 
@example
 function nf90_inq_dimid(ncid, name, dimid)
   integer,             intent( in) :: ncid
   character (len = *), intent( in) :: name
   integer,             intent(out) :: dimid
   integer                          :: nf90_inq_dimid
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item name
Dimension name.
 
@item dimid
Returned dimension ID.
@end table
 
@heading Errors 

NF90_INQ_DIMID returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The name that was specified is not the name of a dimension in the
netCDF dataset.  

@item
The specified netCDF ID does not refer to an open netCDF dataset.

@end itemize

@heading Example 

Here is an example using NF90_INQ_DIMID to determine the dimension ID of
a dimension named lat, assumed to have been defined previously in an
existing netCDF dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid, status, LatDimID
 ...
 status = nf90_open("foo.nc", nf90_nowrite, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 status = nf90_inq_dimid(ncid, "Lat", LatDimID) 
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_INQUIRE_DIMENSION, NF90_RENAME_DIM, NF90_INQ_DIMID, Dimensions
@section NF90_INQUIRE_DIMENSION 
@findex NF90_INQUIRE_DIMENSION 
@cindex NF90_INQUIRE_DIMENSION , example

This function information about a netCDF dimension. Information about
a dimension includes its name and its length. The length for the
unlimited dimension, if any, is the number of records written so far.

@heading Usage 

@example
 function nf90_inquire_dimension(ncid, dimid, name, len)
   integer,                       intent( in) :: ncid, dimid
   character (len = *), optional, intent(out) :: name
   integer,             optional, intent(out) :: len
   integer                                    :: nf90_inquire_dimension
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item dimid
Dimension ID, from a previous call to NF90_INQ_DIMID or NF90_DEF_DIM.
 
@item name
Returned dimension name. The caller must allocate space for the
returned name. The maximum possible length, in characters, of a
dimension name is given by the predefined constant NF90_MAX_NAME.
 
@item len
Returned length of dimension. For the unlimited dimension, this is the
current maximum value used for writing any variables with this
dimension, that is the maximum record number.
@end table

@heading Errors 

These functions return the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The dimension ID is invalid for the specified netCDF dataset. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@end itemize

@heading Example 

Here is an example using NF90_INQ_DIM to determine the length of a
dimension named lat, and the name and current maximum length of the
unlimited dimension for an existing netCDF dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid, status, LatDimID, RecordDimID
 integer :: nLats, nRecords
 character(len = nf90_max_name) :: RecordDimName
 ...
 status = nf90_open("foo.nc", nf90_nowrite, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ! Get ID of unlimited dimension
 status = nf90_inquire(ncid, unlimitedDimId = RecordDimID)
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 status = nf90_inq_dimid(ncid, "Lat", LatDimID) 
 if (status /= nf90_noerr) call handle_err(status)
 ! How many values of "lat" are there?
 status = nf90_inquire_dimension(ncid, LatDimID, len = nLats)
 if (status /= nf90_noerr) call handle_err(status)
 ! What is the name of the unlimited dimension, how many records are there?
 status = nf90_inquire_dimension(ncid, RecordDimID, &
                                 name = RecordDimName, len = Records)
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_RENAME_DIM,  , NF90_INQUIRE_DIMENSION, Dimensions
@section NF90_RENAME_DIM 
@findex NF90_RENAME_DIM 
@cindex NF90_RENAME_DIM , example

The function NF90_RENAME_DIM renames an existing dimension in a netCDF
dataset open for writing. If the new name is longer than the old name,
the netCDF dataset must be in define mode. You cannot rename a
dimension to have the same name as another dimension.

@heading Usage 

@example
 function nf90_rename_dim(ncid, dimid, name)
   integer,             intent( in) :: ncid
   character (len = *), intent( in) :: name
   integer,             intent( in) :: dimid
   integer                          :: nf90_rename_dim
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item dimid
Dimension ID, from a previous call to NF90_INQ_DIMID or NF90_DEF_DIM.
 
@item name
New dimension name.

@end table

@heading Errors 

NF90_RENAME_DIM returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The new name is the name of another dimension. 

@item
The dimension ID is invalid for the specified netCDF dataset. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@item
The new name is longer than the old name and the netCDF dataset is not
in define mode.
@end itemize

@heading Example 
Here is an example using NF90_RENAME_DIM to rename the dimension lat to
latitude in an existing netCDF dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid, status, LatDimID
 ...
 status = nf90_open("foo.nc", nf90_write, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 ! Put in define mode so we can rename the dimension
 status = nf90_redef(ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ! Get the dimension ID for "Lat"...
 status = nf90_inq_dimid(ncid, "Lat", LatDimID)
 if (status /= nf90_noerr) call handle_err(status)
 ! ... and change the name to "Latitude". 
 status = nf90_rename_dim(ncid, LatDimID, "Latitude")
 if (status /= nf90_noerr) call handle_err(status)
 ! Leave define mode
 status = nf90_enddef(ncid)
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node User Defined Data Types, Variables, Dimensions, Top
@chapter User Defined Data Types
@cindex variable length array type, overview
@cindex user defined types

@menu
* User Defined Types::          
* NF90_INQ_TYPEIDS::            
* nf90_inq_typeid::             
* NF90_INQ_TYPE::               
* NF90_INQ_USER_TYPE::          
* Compound Types::              
* Variable Length Array::       
* Opaque Type::                 
* Enum Type::                   
@end menu

@node User Defined Types, NF90_INQ_TYPEIDS, User Defined Data Types, User Defined Data Types
@section User Defined Types Introduction
@cindex user defined types, overview

NetCDF-4 has added support for four different user defined data types.

@table @code

@item compound type
Like a C struct, a compound type is a collection of types, including
other user defined types, in one package.

@item variable length array type
The variable length array may be used to store ragged arrays.

@item opaque type
This type has only a size per element, and no other type information.

@item enum type
Like an enumeration in C, this type lets you assign text values to
integer values, and store the integer values.

@end table

Users may construct user defined type with the various NF90_DEF_*
functions described in this section. They may learn about user defined
types by using the NF90_INQ_ functions defined in this section.

Once types are constructed, define variables of the new type with
NF90_DEF_VAR (@pxref{NF90_DEF_VAR}). Write to them with NF90_PUT_VAR
(@pxref{NF90_PUT_VAR}). Read data of user-defined type with
NF90_GET_VAR (@pxref{NF90_GET_VAR}).

Create attributes of the new type with NF90_PUT_ATT
(@pxref{NF90_PUT_ATT}). Read attributes of the new type with
NF90_GET_ATT (@pxref{NF90_GET_ATT}).

@node NF90_INQ_TYPEIDS, nf90_inq_typeid, User Defined Types, User Defined Data Types
@section Learn the IDs of All Types in Group: NF90_INQ_TYPEIDS
@findex NF90_INQ_TYPEIDS

Learn the number of types defined in a group, and their IDs.

@heading Usage 

@example
  function nf90_inq_typeids(ncid, ntypes, typeids)
    integer, intent(in) :: ncid
    integer, intent(out) :: ntypes
    integer, intent(out) :: typeids
    integer :: nf90_inq_typeids
@end example

@table @code

@item NCID
The group id.

@item NTYPES
A pointer to int which will get the number of types defined in the
group. If NULL, ignored.

@item TYPEIDS
A pointer to an int array which will get the typeids. If NULL,
ignored.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_BADID
Bad ncid.

@end table

@heading Example

@example
@end example

@node nf90_inq_typeid, NF90_INQ_TYPE, NF90_INQ_TYPEIDS, User Defined Data Types
@section Find a Typeid from Group and Name: nf90_inq_typeid
@findex nf90_inq_typeid

Given a group ID and a type name, find the ID of the type. If the type
is not found in the group, then the parents are searched. If still not
found, the entire file is searched.

@heading Usage 

@example
int nf90_inq_typeid(int ncid, char *name, nf90_type *typeidp);
@end example

@table @code

@item ncid
The group id.

@item name
The name of a type.

@item typeidp
The typeid, if found.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad ncid.

@item NF90_EBADTYPE
Can't find type.

@end table

@heading Example

@example
@end example

@node NF90_INQ_TYPE, NF90_INQ_USER_TYPE, nf90_inq_typeid, User Defined Data Types
@section Learn About a User Defined Type: NF90_INQ_TYPE
@findex NF90_INQ_TYPE

Given an ncid and a typeid, get the information about a type. This
function will work on any type, including atomic and any user defined
type, whether compound, opaque, enumeration, or variable length array.

For even more information about a user defined type @ref{NF90_INQ_USER_TYPE}.

@heading Usage 

@example
  function nf90_inq_type(ncid, xtype, name, size, nfields)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(out) :: name
    integer, intent(out) :: size
    integer, intent(out) :: nfields
    integer :: nf90_inq_type
@end example

@table @code

@item NCID
The ncid for the group containing the type (ignored for atomic types).

@item XTYPE
The typeid for this type, as returned by NF90_DEF_COMPOUND,
NF90_DEF_OPAQUE, NF90_DEF_ENUM, NF90_DEF_VLEN, or NF90_INQ_VAR, or as found in
netcdf.inc in the list of atomic types (NF90_CHAR, NF90_INT, etc.).

@item NAME
The name of the user defined type will be copied here. It will be
NF90_MAX_NAME bytes or less. For atomic types, the type name from CDL
will be given.

@item SIZEP
The (in-memory) size of the type (in bytes) will be copied here. VLEN
type size is the size of one element of the VLEN. String size is
returned as the size of one char.

@end table

@heading Return Codes

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPEID
Bad typeid.

@item NF90_ENOTNC4
Seeking a user-defined type in a netCDF-3 file.

@item NF90_ESTRICTNC3
Seeking a user-defined type in a netCDF-4 file for which classic model
has been turned on.

@item NF90_EBADGRPID
Bad group ID in ncid.

@item NF90_EBADID
Type ID not found.

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
@end example

@node NF90_INQ_USER_TYPE, Compound Types, NF90_INQ_TYPE, User Defined Data Types
@section Learn About a User Defined Type: NF90_INQ_USER_TYPE
@findex NF90_INQ_USER_TYPE

Given an ncid and a typeid, get the information about a user defined
type. This function will work on any user defined type, whether
compound, opaque, enumeration, or variable length array.

@heading Usage 

@example
  function nf90_inq_user_type(ncid, xtype, name, size, base_typeid, nfields, class)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(out) :: name
    integer, intent(out) :: size
    integer, intent(out) :: base_typeid
    integer, intent(out) :: nfields
    integer, intent(out) :: class
    integer :: nf90_inq_user_type
@end example

@table @code

@item NCID
The ncid for the group containing the user defined type.

@item XTYPE
The typeid for this type, as returned by NF90_DEF_COMPOUND,
NF90_DEF_OPAQUE, NF90_DEF_ENUM, NF90_DEF_VLEN, or NF90_INQ_VAR.

@item NAME
The name of the user defined type will be copied here. It
will be NF90_MAX_NAME bytes or less.

@item SIZE
The (in-memory) size of the user defined type will be copied here.

@item BASE_NF90_TYPE
The base typeid will be copied here for vlen and enum types.

@item NFIELDS
The number of fields will be copied here for enum and compound types.

@item CLASS
The class of the user defined type, NF90_VLEN, NF90_OPAQUE, NF90_ENUM, or
NF90_COMPOUND, will be copied here.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPEID
Bad typeid.

@item NF90_EBADFIELDID
Bad fieldid.

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
@end example

@menu
* NF90_PUT_VLEN_ELEMENT::       
* NF90_GET_VLEN_ELEMENT::       
@end menu

@node NF90_PUT_VLEN_ELEMENT, NF90_GET_VLEN_ELEMENT, NF90_INQ_USER_TYPE, NF90_INQ_USER_TYPE
@subsection Set a Variable Length Array with NF90_PUT_VLEN_ELEMENT
@findex NF90_PUT_VLEN_ELEMENT

Use this to set the element of the (potentially) n-dimensional array
of VLEN. That is, this sets the data in one variable length array.

@heading Usage

@example
INTEGER FUNCTION NF90_PUT_VLEN_ELEMENT(INTEGER NCID, INTEGER XTYPE,
        CHARACTER*(*) VLEN_ELEMENT, INTEGER LEN, DATA)
@end example

@table @code

@item NCID
The ncid of the file that contains the VLEN type.

@item XTYPE
The type of the VLEN.

@item VLEN_ELEMENT
The VLEN element to be set.

@item LEN
The number of entries in this array.

@item DATA
The data to be stored. Must match the base type of this VLEN.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPE
Can't find the typeid.

@item NF90_EBADID
ncid invalid.

@item NF90_EBADGRPID
Group ID part of ncid was invalid.

@end table

@heading Example

This example is from nf90_test/ftst_vars4.F.

@example
C     Set up the vlen with this helper function, since F77 can't deal
C     with pointers.
      retval = nf90_put_vlen_element(ncid, vlen_typeid, vlen, 
     &     vlen_len, data1)
      if (retval .ne. nf90_noerr) call handle_err(retval)
@end example

@node NF90_GET_VLEN_ELEMENT,  , NF90_PUT_VLEN_ELEMENT, NF90_INQ_USER_TYPE
@subsection Set a Variable Length Array with NF90_GET_VLEN_ELEMENT
@findex NF90_GET_VLEN_ELEMENT

Use this to set the element of the (potentially) n-dimensional array
of VLEN. That is, this sets the data in one variable length array.

@heading Usage

@example
INTEGER FUNCTION NF90_GET_VLEN_ELEMENT(INTEGER NCID, INTEGER XTYPE,
        CHARACTER*(*) VLEN_ELEMENT, INTEGER LEN, DATA)
@end example

@table @code

@item NCID
The ncid of the file that contains the VLEN type.

@item XTYPE
The type of the VLEN.

@item VLEN_ELEMENT
The VLEN element to be set.

@item LEN
This will be set to the number of entries in this array.

@item DATA
The data will be copied here. Sufficient storage must be available or
bad things will happen to you.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPE
Can't find the typeid.

@item NF90_EBADID
ncid invalid.

@item NF90_EBADGRPID
Group ID part of ncid was invalid.

@end table

@heading Example

@example
@end example

@node Compound Types, Variable Length Array, NF90_INQ_USER_TYPE, User Defined Data Types
@section Compound Types Introduction
@cindex compound types, overview

NetCDF-4 added support for compound types, which allow users to
construct a new type - a combination of other types, like a C struct.

Compound types are not supported in classic or 64-bit offset format
files. 

To write data in a compound type, first use nf90_def_compound to create the
type, multiple calls to nf90_insert_compound to add to the compound type, and
then write data with the appropriate nf90_put_var1, nf90_put_vara,
nf90_put_vars, or nf90_put_varm call.

To read data written in a compound type, you must know its
structure. Use the NF90_INQ_COMPOUND functions to learn about the compound
type.

In Fortran a character buffer must be used for the compound data. The
user must read the data from within that buffer in the same way that
the C compiler which compiled netCDF would store the structure.

The use of compound types introduces challenges and portability issues
for Fortran users.

@menu
* NF90_DEF_COMPOUND::           
* NF90_INSERT_COMPOUND::        
* NF90_INSERT_ARRAY_COMPOUND::  
* NF90_INQ_COMPOUND::           
* NF90_INQ_COMPOUND_FIELD::     
@end menu

@node NF90_DEF_COMPOUND, NF90_INSERT_COMPOUND, Compound Types, Compound Types
@subsection Creating a Compound Type: NF90_DEF_COMPOUND
@findex NF90_DEF_COMPOUND

Create a compound type. Provide an ncid, a name, and a total size (in
bytes) of one element of the completed compound type.

After calling this function, fill out the type with repeated calls to
NF90_INSERT_COMPOUND (@pxref{NF90_INSERT_COMPOUND}). Call
NF90_INSERT_COMPOUND once for each field you wish to insert into the
compound type.

Note that there does not seem to be a fully portable way to read such
types into structures in Fortran 90 (and there are no structures in
Fortran 77). Dozens of top-notch programmers are swarming over this
problem in a sub-basement of Unidata's giant underground bunker in
Wyoming.

Fortran users may use character buffers to read and write compound
types. User are invited to try classic Fortran features such as the
equivilence and the common block statement. 

@heading Usage 

@example
  function nf90_def_compound(ncid, size, name, typeid)
    integer, intent(in) :: ncid
    integer, intent(in) :: size
    character (len = *), intent(in) :: name
    integer, intent(out) :: typeid
    integer :: nf90_def_compound
@end example

@table @code

@item NCID
The groupid where this compound type will be created.

@item SIZE
The size, in bytes, of the compound type. 

@item NAME
The name of the new compound type.

@item TYPEIDP
The typeid of the new type will be placed here.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENAMEINUSE
That name is in use. Compound type names must be unique in the data
file. 

@item NF90_EMAXNAME
Name exceeds max length NF90_MAX_NAME.

@item NF90_EBADNAME
Name contains illegal characters.

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag NF90_NETCDF4. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@item NF90_EPERM
Attempt to write to a read-only file.

@item NF90_ENOTINDEFINE
Not in define mode.

@end table

@heading Example

@example
@end example

@node NF90_INSERT_COMPOUND, NF90_INSERT_ARRAY_COMPOUND, NF90_DEF_COMPOUND, Compound Types
@subsection Inserting a Field into a Compound Type: NF90_INSERT_COMPOUND
@findex NF90_INSERT_COMPOUND

Insert a named field into a compound type.

@heading Usage 

@example
  function nf90_insert_compound(ncid, xtype, name, offset, field_typeid)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(in) :: name
    integer, intent(in) :: offset
    integer, intent(in) :: field_typeid
    integer :: nf90_insert_compound
@end example

@table @code

@item TYPEID
The typeid for this compound type, as returned by NF90_DEF_COMPOUND, or
NF90_INQ_VAR.

@item NAME
The name of the new field.

@item OFFSET
Offset in byte from the beginning of the compound type for this
field.

@item FIELD_TYPEID
The type of the field to be inserted.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENAMEINUSE
That name is in use. Field names must be unique within a compound type.

@item NF90_EMAXNAME
Name exceed max length NF90_MAX_NAME.

@item NF90_EBADNAME
Name contains illegal characters.

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag NF90_NETCDF4. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@item NF90_ENOTINDEFINE
Not in define mode.

@end table

@heading Example

@example
@end example

@node NF90_INSERT_ARRAY_COMPOUND, NF90_INQ_COMPOUND, NF90_INSERT_COMPOUND, Compound Types
@subsection Inserting an Array Field into a Compound Type: NF90_INSERT_ARRAY_COMPOUND
@findex NF90_INSERT_ARRAY_COMPOUND

Insert a named array field into a compound type.

@heading Usage 

@example
  function nf90_insert_array_compound(ncid, xtype, name, offset, field_typeid, &
       ndims, dim_sizes)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(in) :: name
    integer, intent(in) :: offset
    integer, intent(in) :: field_typeid
    integer, intent(in) :: ndims
    integer, intent(in) :: dim_sizes
    integer :: nf90_insert_array_compound
@end example

@table @code

@item NCID
The ID of the file that contains the array type and the compound type.

@item XTYPE
The typeid for this compound type, as returned by nf90_def_compound, or
nf90_inq_var.

@item NAME
The name of the new field.

@item OFFSET
Offset in byte from the beginning of the compound type for this
field.

@item FIELD_TYPEID
The base type of the array to be inserted.

@item NDIMS
The number of dimensions for the array to be inserted.

@item DIM_SIZES
An array containing the sizes of each dimension.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENAMEINUSE
That name is in use. Field names must be unique within a compound type.

@item NF90_EMAXNAME
Name exceed max length NF90_MAX_NAME.

@item NF90_EBADNAME
Name contains illegal characters.

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag NF90_NETCDF4. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@item NF90_ENOTINDEFINE
Not in define mode.

@item NF90_ETYPEDEFINED
Attempt to change type that has already been committed. The first time
the file leaves define mode, all defined types are committed, and
can't be changed. If you wish to add an array to a compound type, you
must do so before the compound type is committed.

@end table

@heading Example

@example
@end example

@node NF90_INQ_COMPOUND, NF90_INQ_COMPOUND_FIELD, NF90_INSERT_ARRAY_COMPOUND, Compound Types
@subsection Learn About a Compound Type: NF90_INQ_COMPOUND
@findex NF90_INQ_COMPOUND
@findex NF90_INQ_COMPOUND_NAME
@findex NF90_INQ_COMPOUND_SIZE
@findex NF90_INQ_COMPOUND_NFIELDS

Get the number of fields, length in bytes, and name of a compound
type.

In addition to the NF90_INQ_COMPOUND function, three additional functions
are provided which get only the name, size, and number of fields.

@heading Usage 

@example
  function nf90_inq_compound(ncid, xtype, name, size, nfields)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(out) :: name
    integer, intent(out) :: size
    integer, intent(out) :: nfields
    integer :: nf90_inq_compound

  function nf90_inq_compound_name(ncid, xtype, name)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(out) :: name
    integer :: nf90_inq_compound_name

  function nf90_inq_compound_size(ncid, xtype, size)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    integer, intent(out) :: size
    integer :: nf90_inq_compound_size

  function nf90_inq_compound_nfields(ncid, xtype, nfields)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    integer, intent(out) :: nfields
    integer :: nf90_inq_compound_nfields
@end example

@table @code

@item NCID
The ID of any group in the file that contains the compound type.

@item XTYPE
The typeid for this compound type, as returned by NF90_DEF_COMPOUND, or
NF90_INQ_VAR.

@item NAME
Character array which will get the name of the compound type. It will
have a maximum length of NF90_MAX_NAME.

@item SIZEP
The size of the compound type in bytes will be put here.

@item NFIELDSP
The number of fields in the compound type will be placed here.

@end table

@heading Return Codes

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Couldn't find this ncid.

@item NF90_ENOTNC4
Not a netCDF-4/HDF5 file.

@item NF90_ESTRICTNC3
A netCDF-4/HDF5 file, but with CLASSIC_MODEL. No user defined types
are allowed in the classic model.

@item NF90_EBADTYPE
This type not a compound type.

@item NF90_EBADTYPEID
Bad type id. 

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
@end example

@node NF90_INQ_COMPOUND_FIELD,  , NF90_INQ_COMPOUND, Compound Types
@subsection Learn About a Field of a Compound Type: NF90_INQ_COMPOUND_FIELD
@findex NF90_INQ_COMPOUND_FIELD
@findex NF90_INQ_COMPOUND_FIELDNAME
@findex NF90_INQ_COMPOUND_FIELDINDEX
@findex NF90_INQ_COMPOUND_FIELDOFFSET
@findex NF90_INQ_COMPOUND_FIELDTYPE
@findex NF90_INQ_COMPOUND_FIELDNDIMS
@findex NF90_INQ_CMP_FIELDDIM_SIZES

Get information about one of the fields of a compound type.

@heading Usage 

@example
  function nf90_inq_compound_field(ncid, xtype, fieldid, name, offset, &
       field_typeid, ndims, dim_sizes)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    integer, intent(in) :: fieldid
    character (len = *), intent(out) :: name
    integer, intent(out) :: offset
    integer, intent(out) :: field_typeid
    integer, intent(out) :: ndims
    integer, intent(out) :: dim_sizes
    integer :: nf90_inq_compound_field

  function nf90_inq_compound_fieldname(ncid, xtype, fieldid, name)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    integer, intent(in) :: fieldid
    character (len = *), intent(out) :: name
    integer :: nf90_inq_compound_fieldname
  
  function nf90_inq_compound_fieldindex(ncid, xtype, name, fieldid)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(in) :: name
    integer, intent(out) :: fieldid
    integer :: nf90_inq_compound_fieldindex
  
  function nf90_inq_compound_fieldoffset(ncid, xtype, fieldid, offset)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    integer, intent(in) :: fieldid
    integer, intent(out) :: offset
    integer :: nf90_inq_compound_fieldoffset
  
  function nf90_inq_compound_fieldtype(ncid, xtype, fieldid, field_typeid)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    integer, intent(in) :: fieldid
    integer, intent(out) :: field_typeid
    integer :: nf90_inq_compound_fieldtype
  
  function nf90_inq_compound_fieldndims(ncid, xtype, fieldid, ndims)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    integer, intent(in) :: fieldid
    integer, intent(out) :: ndims
    integer :: nf90_inq_compound_fieldndims
  
  function nf90_inq_cmp_fielddim_sizes(ncid, xtype, fieldid, dim_sizes)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    integer, intent(in) :: fieldid
    integer, intent(out) :: dim_sizes
    integer :: nf90_inq_cmp_fielddim_sizes
@end example

@table @code

@item NCID
The groupid where this compound type exists.

@item XTYPE
The typeid for this compound type, as returned by NF90_DEF_COMPOUND, or
NF90_INQ_VAR.

@item FIELDID
A one-based index number specifying a field in the compound type.

@item NAME
A character array which will get the name of the field. The name will
be NF90_MAX_NAME characters, at most.

@item OFFSETP
An integer which will get the offset of the field.

@item FIELD_TYPEID
An integer which will get the typeid of the field.

@item NDIMSP
An integer which will get the number of dimensions of the field.

@item DIM_SIZESP
An integer array which will get the dimension sizes of the field.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPEID
Bad type id. 

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
@end example

@node Variable Length Array, Opaque Type, Compound Types, User Defined Data Types
@section Variable Length Array Introduction
@cindex variable length arrays
@cindex VLEN

NetCDF-4 added support for a variable length array type. This is not
supported in classic or 64-bit offset files, or in netCDF-4 files
which were created with the NF90_CLASSIC_MODEL flag.

A variable length array is represented in C as a structure from HDF5,
the nf90_vlen_t structure. It contains a len member, which contains the
length of that array, and a pointer to the array.

So an array of VLEN in C is an array of nc_vlen_t structures. The only
way to handle this in Fortran is with a character buffer sized
correctly for the platform.

VLEN arrays are handled differently with respect to allocation of
memory. Generally, when reading data, it is up to the user to malloc
(and subsequently free) the memory needed to hold the data. It is up to
the user to ensure that enough memory is allocated.

With VLENs, this is impossible. The user cannot know the size of an
array of VLEN until after reading the array. Therefore when reading
VLEN arrays, the netCDF library will allocate the memory for the data within
each VLEN.

It is up to the user, however, to eventually free this memory. This is
not just a matter of one call to free, with the pointer to the array
of VLENs; each VLEN contains a pointer which must be freed.

Compression is permitted but may not be effective for VLEN data,
because the compression is applied to the nc_vlen_t structures, rather
than the actual data.

@menu
* NF90_DEF_VLEN::               
* NF90_INQ_VLEN::               
* NF90_FREE_VLEN::              
@end menu

@node NF90_DEF_VLEN, NF90_INQ_VLEN, Variable Length Array, Variable Length Array
@subsection Define a Variable Length Array (VLEN): NF90_DEF_VLEN
@findex NF90_DEF_VLEN
@cindex VLEN, defining

Use this function to define a variable length array type. 

@heading Usage

@example
  function nf90_def_vlen(ncid, name, base_typeid, xtypeid)
    integer, intent(in) :: ncid
    character (len = *), intent(in) :: name
    integer, intent(in) :: base_typeid
    integer, intent(out) :: xtypeid
    integer :: nf90_def_vlen
@end example

@table @code

@item NCID
The ncid of the file to create the VLEN type in.

@item NAME 
A name for the VLEN type.

@item BASE_TYPEID
The typeid of the base type of the VLEN. For example, for a VLEN of
shorts, the base type is NF90_SHORT. This can be a user defined type.

@item XTYPEP
The typeid of the new VLEN type will be set here.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EMAXNAME
NF90_MAX_NAME exceeded.

@item NF90_ENAMEINUSE
Name is already in use.

@item NF90_EBADNAME
Attribute or variable name contains illegal characters.

@item NF90_EBADID
ncid invalid.

@item NF90_EBADGRPID
Group ID part of ncid was invalid.

@item NF90_EINVAL
Size is invalid.

@item NF90_ENOMEM
Out of memory.

@end table

@heading Example

@example
@end example

@node NF90_INQ_VLEN, NF90_FREE_VLEN, NF90_DEF_VLEN, Variable Length Array
@subsection Learning about a Variable Length Array (VLEN) Type: NF90_INQ_VLEN
@findex NF90_INQ_VLEN
@cindex VLEN, defining

Use this type to learn about a vlen.

@heading Usage

@example
  function nf90_inq_vlen(ncid, xtype, name, datum_size, base_nc_type)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(out) :: name
    integer, intent(out) :: datum_size
    integer, intent(out) :: base_nc_type
    integer :: nf90_inq_vlen
@end example

@table @code

@item NCID
The ncid of the file that contains the VLEN type.

@item XTYPE
The type of the VLEN to inquire about.

@item NAME
The name of the VLEN type. The name will be NF90_MAX_NAME characters or
less.

@item DATUM_SIZEP
A pointer to a size_t, this will get the size of one element of this
vlen.

@item BASE_NF90_TYPEP
An integer that will get the type of the VLEN base type. (In other
words, what type is this a VLEN of?)

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPE
Can't find the typeid.

@item NF90_EBADID
ncid invalid.

@item NF90_EBADGRPID
Group ID part of ncid was invalid.

@end table

@heading Example

@example
@end example

@node NF90_FREE_VLEN,  , NF90_INQ_VLEN, Variable Length Array
@subsection Releasing Memory for a Variable Length Array (VLEN) Type: NF90_FREE_VLEN
@findex NF90_FREE_VLEN
@cindex VLEN, defining

When a VLEN is read into user memory from the file, the HDF5 library
performs memory allocations for each of the variable length arrays
contained within the VLEN structure. This memory must be freed by the
user to avoid memory leaks.

This violates the normal netCDF expectation that the user is
responsible for all memory allocation. But, with VLEN arrays, the
underlying HDF5 library allocates the memory for the user, and the user
is responsible for deallocating that memory.

@heading Usage

@example
  function nf90_free_vlen(vl)
    character (len = *), intent(in) :: vlen
    integer :: nf90_free_vlen
  end function nf90_free_vlen
@end example

@table @code

@item VL
The variable length array structure which is to be freed.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPE
Can't find the typeid.

@end table

@heading Example

@example
@end example

@node Opaque Type, Enum Type, Variable Length Array, User Defined Data Types
@section Opaque Type Introduction
@cindex opaque type

NetCDF-4 added support for the opaque type. This is not supported in
classic or 64-bit offset files.

The opaque type is a type which is a collection of objects of a known
size. (And each object is the same size). Nothing is known to netCDF
about the contents of these blobs of data, except their size in bytes,
and the name of the type.

To use an opaque type, first define it with @ref{NF90_DEF_OPAQUE}. If
encountering an enum type in a new data file, use @ref{NF90_INQ_OPAQUE}
to learn its name and size.

@menu
* NF90_DEF_OPAQUE::             
* NF90_INQ_OPAQUE::             
@end menu

@node NF90_DEF_OPAQUE, NF90_INQ_OPAQUE, Opaque Type, Opaque Type
@subsection Creating Opaque Types: NF90_DEF_OPAQUE
@findex NF90_DEF_OPAQUE

Create an opaque type. Provide a size and a name.

@heading Usage 

@example
  function nf90_def_opaque(ncid, size, name, xtype)
    integer, intent(in) :: ncid
    integer, intent(in) :: size
    character (len = *), intent(in) :: name
    integer, intent(out) :: xtype
    integer :: nf90_def_opaque
@end example

@table @code

@item NCID
The groupid where the type will be created. The type may be used
anywhere in the file, no matter what group it is in.

@item NAME
The name for this type. Must be shorter than NF90_MAX_NAME.

@item SIZE
The size of each opaque object.

@item TYPEIDP
Pointer where the new typeid for this type is returned. Use this
typeid when defining variables of this type with @ref{NF90_DEF_VAR}.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPEID
Bad typeid.

@item NF90_EBADFIELDID
Bad fieldid.

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
@end example

@menu
* NF90_INQ_OPAQUE::               
@end menu

@node NF90_INQ_OPAQUE,  , NF90_DEF_OPAQUE, Opaque Type
@subsection Learn About an Opaque Type: NF90_INQ_OPAQUE
@findex NF90_INQ_OPAQUE

Given a typeid, get the information about an opaque type.

@heading Usage 

@example
  function nf90_inq_opaque(ncid, xtype, name, size)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(out) :: name
    integer, intent(out) :: size
    integer :: nf90_inq_opaque
@end example

@table @code

@item NCID
The ncid for the group containing the opaque type.

@item XTYPE
The typeid for this opaque type, as returned by NF90_DEF_COMPOUND, or
NF90_INQ_VAR.

@item NAME
The name of the opaque type will be copied here. It will
be NF90_MAX_NAME bytes or less.

@item SIZEP
The size of the opaque type will be copied here.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPEID
Bad typeid.

@item NF90_EBADFIELDID
Bad fieldid.

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
@end example

@node Enum Type,  , Opaque Type, User Defined Data Types
@section Enum Type Introduction
@cindex enum type

NetCDF-4 added support for the enum type. This is not supported in
classic or 64-bit offset files.

@menu
* NF90_DEF_ENUM::               
* NF90_INSERT_ENUM::            
* NF90_INQ_ENUM::               
* NF90_INQ_ENUM_MEMBER::        
* NF90_INQ_ENUM_IDENT::         
@end menu

@node NF90_DEF_ENUM, NF90_INSERT_ENUM, Enum Type, Enum Type
@subsection Creating a Enum Type: NF90_DEF_ENUM
@findex NF90_DEF_ENUM

Create an enum type. Provide an ncid, a name, and a base integer
type. 

After calling this function, fill out the type with repeated calls to
NF90_INSERT_ENUM (@pxref{NF90_INSERT_ENUM}). Call NF90_INSERT_ENUM once for
each value you wish to make part of the enumeration.

@heading Usage 

@example
  function nf90_def_enum(ncid, base_typeid, name, typeid)
    integer, intent(in) :: ncid
    integer, intent(in) :: base_typeid
    character (len = *), intent(in) :: name
    integer, intent(out) :: typeid
    integer :: nf90_def_enum
@end example

@table @code

@item NCID
The groupid where this compound type will be created.

@item BASE_TYPEID
The base integer type for this enum. Must be one of: NF90_BYTE,
NF90_UBYTE, NF90_SHORT, NF90_USHORT, NF90_INT, NF90_UINT, NF90_INT64, NF90_UINT64.

@item NAME
The name of the new enum type.

@item TYPEIDP
The typeid of the new type will be placed here.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENAMEINUSE
That name is in use. Compound type names must be unique in the data
file. 

@item NF90_EMAXNAME
Name exceeds max length NF90_MAX_NAME.

@item NF90_EBADNAME
Name contains illegal characters.

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag NF90_NETCDF4. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@item NF90_EPERM
Attempt to write to a read-only file.

@item NF90_ENOTINDEFINE
Not in define mode.

@end table

@heading Example

@example
@end example

@node NF90_INSERT_ENUM, NF90_INQ_ENUM, NF90_DEF_ENUM, Enum Type
@subsection Inserting a Field into a Enum Type: NF90_INSERT_ENUM
@findex NF90_INSERT_ENUM

Insert a named member into a enum type.

@heading Usage 

@example
  function nf90_insert_enum(ncid, xtype, name, value)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(in) :: name
    integer, intent(in) :: value
    integer :: nf90_insert_enum
@end example

@table @code

@item NCID
The ncid of the group which contains the type.

@item TYPEID
The typeid for this enum type, as returned by nf90_def_enum, or
nf90_inq_var.

@item IDENTIFIER
The identifier of the new member.

@item VALUE
The value that is to be associated with this member.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADID
Bad group id. 

@item NF90_ENAMEINUSE
That name is in use. Field names must be unique within a enum type.

@item NF90_EMAXNAME
Name exceed max length NF90_MAX_NAME.

@item NF90_EBADNAME
Name contains illegal characters.

@item NF90_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag NF90_NETCDF4. (@pxref{NF90_OPEN}).

@item NF90_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{NF90_OPEN}).

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@item NF90_ENOTINDEFINE
Not in define mode.

@end table

@heading Example

@example
@end example

@node NF90_INQ_ENUM, NF90_INQ_ENUM_MEMBER, NF90_INSERT_ENUM, Enum Type
@subsection Learn About a Enum Type: NF90_INQ_ENUM
@findex NF90_INQ_ENUM

Get information about a user-defined enumeration type.

@heading Usage 

@example
  function nf90_inq_enum(ncid, xtype, name, base_nc_type, base_size, num_members)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    character (len = *), intent(out) :: name
    integer, intent(out) :: base_nc_type
    integer, intent(out) :: base_size
    integer, intent(out) :: num_members
    integer :: nf90_inq_enum
@end example

@table @code

@item NCID
The group ID of the group which holds the enum type.

@item XTYPE
The typeid for this enum type, as returned by NF90_DEF_ENUM, or
NF90_INQ_VAR.

@item NAME
Character array which will get the name. It will have a maximum length
of NF90_MAX_NAME.

@item BASE_NF90_TYPE
An integer which will get the base integer type of this enum.

@item BASE_SIZE
An integer which will get the size (in bytes) of the base integer type
of this enum.

@item NUM_MEMBERS
An integer which will get the number of members defined for this
enumeration type.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPEID
Bad type id. 

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
@end example

@node NF90_INQ_ENUM_MEMBER, NF90_INQ_ENUM_IDENT, NF90_INQ_ENUM, Enum Type
@subsection Learn the Name of a Enum Type: nf90_inq_enum_member
@findex nf90_inq_enum_member

Get information about a member of an enum type.

@heading Usage 

@example
  function nf90_inq_enum_member(ncid, xtype, idx, name, value)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    integer, intent(in) :: idx
    character (len = *), intent(out) :: name
    integer, intent(in) :: value
    integer :: nf90_inq_enum_member
@end example

@table @code

@item NCID
The groupid where this enum type exists.

@item XTYPE
The typeid for this enum type.

@item IDX
The one-based index number for the member of interest. 

@item NAME
A character array which will get the name of the member. It will have
a maximum length of NF90_MAX_NAME.

@item VALUE
An integer that will get the value associated with this member.

@end table

@heading Errors

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPEID
Bad type id. 

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
@end example

@node NF90_INQ_ENUM_IDENT,  , NF90_INQ_ENUM_MEMBER, Enum Type
@subsection Learn the Name of a Enum Type: NF90_INQ_ENUM_IDENT
@findex NF90_INQ_ENUM_IDENT

Get the name which is associated with an enum member value.

This is similar to NF90_INQ_ENUM_MEMBER, but instead of using the index
of the member, you use the value of the member.

@heading Usage 

@example
  function nf90_inq_enum_ident(ncid, xtype, value, idx)
    integer, intent(in) :: ncid
    integer, intent(in) :: xtype
    integer, intent(in) :: value
    integer, intent(out) :: idx
    integer :: nf90_inq_enum_ident
@end example

@table @code

@item NCID
The groupid where this enum type exists.

@item XTYPE
The typeid for this enum type.

@item VALUE
The value for which an identifier is sought.

@item IDENTIFIER
A character array that will get the identifier. It will have a maximum
length of NF90_MAX_NAME.

@end table

@heading Return Code

@table @code

@item NF90_NOERR
No error.

@item NF90_EBADTYPEID
Bad type id, or not an enum type.

@item NF90_EHDFERR
An error was reported by the HDF5 layer.

@item NF90_EINVAL
The value was not found in the enum.

@end table

@heading Example

@example
@end example

@node Variables, Attributes, User Defined Data Types, Top
@chapter Variables

@menu
* Variables Introduction::      
* Language-Types::              
* NF90_DEF_VAR::                Create a Variable
* NF90_DEF_VAR_FILL::           
* NF90_INQ_VAR_FILL::           
* NF90_INQUIRE_VARIABLE::       Get Var Metadata
* NF90_INQ_VARID::              
* NF90_PUT_VAR::                Write data
* NF90_GET_VAR::                Read data
* Reading and Writing Character String Values::  
* Fill Values::                 What's Written Where there's No Data?
* NF90_RENAME_VAR::             
* NF90_VAR_PAR_ACCESS::         
@end menu

@node Variables Introduction, Language-Types, Variables, Variables
@section Variables Introduction

Variables for a netCDF dataset are defined when the dataset is
created, while the netCDF dataset is in define mode. Other variables
may be added later by reentering define mode. A netCDF variable has a
name, a type, and a shape, which are specified when it is defined. A
variable may also have values, which are established later in data
mode.

Ordinarily, the name, type, and shape are fixed when the variable is
first defined. The name may be changed, but the type and shape of a
variable cannot be changed. However, a variable defined in terms of
the unlimited dimension can grow without bound in that dimension.

A netCDF variable in an open netCDF dataset is referred to by a small
integer called a variable ID.

Variable IDs reflect the order in which variables were defined within
a netCDF dataset. Variable IDs are 1, 2, 3,..., in the order in which
the variables were defined. A function is available for getting the
variable ID from the variable name and vice-versa.

Attributes (see @ref{Attributes}) may be associated with a variable to
specify such properties as units.

Operations supported on variables are:
@itemize

@item
Create a variable, given its name, data type, and shape. 

@item
Get a variable ID from its name. 

@item
Get a variable's name, data type, shape, and number of attributes from
its ID.

@item
Put a data value into a variable, given variable ID, indices, and
value.

@item
Put an array of values into a variable, given variable ID, corner
indices, edge lengths, and a block of values.

@item
Put a subsampled or mapped array-section of values into a variable,
given variable ID, corner indices, edge lengths, stride vector, index
mapping vector, and a block of values.

@item
Get a data value from a variable, given variable ID and indices. 

@item
Get an array of values from a variable, given variable ID, corner
indices, and edge lengths.

@item
Get a subsampled or mapped array-section of values from a variable,
given variable ID, corner indices, edge lengths, stride vector, and
index mapping vector.

@item
Rename a variable. 
@end itemize

@node Language-Types, NF90_DEF_VAR, Variables Introduction, Variables
@section Language Types Corresponding to netCDF external data types

The following table gives the netCDF external data types and the
corresponding type constants for defining variables in the Fortran
interface:

@multitable @columnfractions .25 .60 .15
@item Type @tab Fortran API Mnemonic @tab Bits

@item byte
@tab NF90_BYTE 
@tab 8
 
@item char
@tab NF90_CHAR 
@tab 8
 
@item short
@tab NF90_SHORT 
@tab 16
 
@item int
@tab NF90_INT 
@tab 32
 
@item float
@tab NF90_FLOAT 
@tab 32
 
@item double
@tab NF90_DOUBLE 
@tab 64
@end multitable
 
The first column gives the netCDF external data type, which is the
same as the CDL data type. The next column gives the corresponding
Fortran 90 parameter for use in netCDF functions (the parameters are
defined in the netCDF Fortran 90 module netcdf.f90). The last column
gives the number of bits used in the external representation of values
of the corresponding type.

Note that there are no netCDF types corresponding to 64-bit integers
or to characters wider than 8 bits in the current version of the
netCDF library.

@node NF90_DEF_VAR, NF90_DEF_VAR_FILL, Language-Types, Variables
@section Create a Variable: @code{NF90_DEF_VAR} 
@findex NF90_DEF_VAR
@cindex NF90_DEF_VAR, example

The function NF90_DEF_VAR adds a new variable to an open netCDF dataset
in define mode. It returns (as an argument) a variable ID, given the
netCDF ID, the variable name, the variable type, the number of
dimensions, and a list of the dimension IDs.

Optional arguments allow additional settings for variables in
netCDF-4/HDF5 files. These parameters allow data compression and
control of the layout of the data on disk for performance tuning.
These parameters may also be used to set the chunk sizes to get chunked
storage, or to set the contiguous flag to get contiguous storage.

Variables that make use of one or more unlimited dimensions,
compression, or checksums must use chunking.  Such variables are
created with default chunk sizes of 1 for each unlimited dimension and
the dimension length for other dimensions, except that if the
resulting chunks are too large, the default chunk sizes for non-record
dimensions are reduced.

All parameters after the varid are optional, and only supported if
netCDF was built with netCDF-4 features enabled, and if the variable
is in a netCDF-4/HDF5 file.

@heading Usage 
@example
 function nf90_def_var(ncid, name, xtype, dimids, varid, contiguous, &
       chunksizes, deflate_level, shuffle, fletcher32, endianness, &
       cache_size, cache_nelems, cache_preemption)
   integer, intent(in) :: ncid
   character (len = *), intent(in) :: name
   integer, intent( in) :: xtype
   integer, dimension(:), intent(in) :: dimids
   integer, intent(out) :: varid
   logical, optional, intent(in) :: contiguous
   integer, optional, dimension(:), intent(in) :: chunksizes
   integer, optional, intent(in) :: deflate_level
   logical, optional, intent(in) :: shuffle, fletcher32
   integer, optional, intent(in) :: endianness
    integer, optional, intent(in) :: cache_size, cache_nelems, cache_preemption
   integer                                      :: nf90_def_var
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item name
Variable name.
 
@item xtype
One of the set of predefined netCDF external data types. The type of
this parameter, NF90_TYPE, is defined in the netCDF header file. The
valid netCDF external data types are NF90_BYTE, NF90_CHAR, NF90_SHORT,
NF90_INT, NF90_FLOAT, and NF90_DOUBLE. If the file is a NetCDF-4/HDF5 file,
the additional types NF90_UBYTE, NF90_USHORT, NF90_UINT, NF90_INT64,
NF90_UINT64, and NF90_STRING may be used, as well as a user defined type
ID.
 
@item dimids
Vector of dimension IDs corresponding to the variable dimensions. For
example, a vector of 2 dimension IDs specifies a 2-dimensional matrix.

If an integer is passed for this parameter, a 1-D variable is created.

If this parameter is not passed (or is a 1D array of size zero) it
means the variable is a scalar with no dimensions.

For classic data model files, if the ID of the unlimited dimension is
included, it must be first.  In expanded model netCDF4/HDF5 files,
there may be any number of unlimited dimensions, and they may be used
in any element of the dimids array.

This argument is optional, and if absent specifies a scalar with no
dimensions.
 
@item varid
Returned variable ID.

@item storage
If NF90_CONTIGUOUS, then contiguous storage is used for this
variable. Variables that use deflation, shuffle filter, or checksums,
or that have one or more unlimited dimensions cannot use contiguous
storage.

If NF90_CHUNKED, then chunked storage is used for this variable.
Chunk sizes may be specified with the chunksizes parameter.
Default sizes will be used if chunking is required and this function
is not called.

By default contiguous storage is used for fix-sized variables when
conpression, chunking, shuffle, and checksums are not used.

@item chunksizes
An array of chunk number of elements. This array has the number of
elements along each dimension of the data chunk. The array must have
the one chunksize for each dimension in the variable.

The total size of a chunk must be less than 4 GiB. That is, the product
of all chunksizes and the size of the data (or the size of nc_vlen_t
for VLEN types) must be less than 4 GiB. (This is a very large chunk
size in any case.)

If not provided, but chunked data are needed, then default chunksizes
will be chosen. For more information see @ref{Chunking,
@value{n-man},, netcdf, @value{n-man}}.

@item shuffle
If non-zero, turn on the shuffle filter.

@item deflate_level
If the deflate parameter is non-zero, set the deflate level to this
value. Must be between 1 and 9.

@item fletcher32
Set to true to turn on fletcher32 checksums for this variable.
 
@item endianness
Set to NF90_ENDIAN_LITTLE for little-endian format, NF90_ENDIAN_BIG
for big-endian format, and NF90_ENDIAN_NATIVE (the default) for the
native endianness of the platform.

@item cache_size
The size of the per-variable cache in MegaBytes.

@item cache_nelems
The number slots in the per-variable chunk cache (should be a prime number
larger than the number of chunks in the cache).

@item cache_preemption
The preemtion value must be between 0 and 100 inclusive and indicates
how much chunks that have been fully read are favored for
preemption. A value of zero means fully read chunks are treated no
differently than other chunks (the preemption is strictly LRU) while a
value of 100 means fully read chunks are always preempted before other
chunks. 

@end table

@heading Return Codes

NF90_DEF_VAR returns the value NF90_NOERR if no errors occurred.
Otherwise, the returned status indicates an error. 

@itemize

@item NF90_EBADNAME
The specified variable name is the name of another existing variable. 

@item NF90_EBADTYPE
The specified type is not a valid netCDF type. 

@item NF90_EMAXDIMS
The specified number of dimensions is negative or more than the
constant NF90_MAX_VAR_DIMS, the maximum number of dimensions permitted
for a netCDF variable. (Does not apply to netCDF-4/HDF5 files unless they were
created with the CLASSIC_MODE flag.)

@item NF90_EBADDIM
One or more of the dimension IDs in the list of dimensions is not a
valid dimension ID for the netCDF dataset.

@item NF90_EMAXVARS
The number of variables would exceed the constant NF90_MAX_VARS, the
maximum number of variables permitted in a classic netCDF
dataset. (Does not apply to netCDF-4/HDF5 files unless they were
created with the CLASSIC_MODE flag.)

@item NF90_BADID
The specified netCDF ID does not refer to an open netCDF dataset. 

@item NF90_ENOTNC4
NetCDF-4 operation attempted on a files that is not a netCDF-4/HDF5
file. Only variables in NetCDF-4/HDF5 files may use compression,
chunking, and endianness control.

@item NF90_ENOTVAR
Can't find this variable.

@item NF90_EINVAL
Invalid input. This may be because contiguous storage is requested for
a variable that has compression, checksums, chunking, or one or more
unlimited dimensions.

@item NF90_ELATEDEF
This variable has already been the subject of a NF90_ENDDEF call. Once
enddef has been called, it is impossible to set the chunking for a
variable. (In netCDF-4/HDF5 files NF90_ENDDEF will be called
automatically for any data read or write.)

@item NF90_ENOTINDEFINE
Not in define mode. This is returned for netCDF classic or 64-bit
offset files, or for netCDF-4 files, when they were been created with
NF90_STRICT_NC3 flag. (@pxref{NF90_CREATE}).

@item NF90_ESTRICTNC3
Trying to create a var some place other than the root group in a
netCDF file with NF90_STRICT_NC3 turned on.

@end itemize

@heading Example 

Here is an example using NF90_DEF_VAR to create a variable named rh of
type double with three dimensions, time, lat, and lon in a new netCDF
dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: status, ncid
 integer :: LonDimId, LatDimId, TimeDimId
 integer :: RhVarId
 ...
 status = nf90_create("foo.nc", nf90_NoClobber, ncid)
 if(status /= nf90_NoErr) call handle_error(status)
 ...
 ! Define the dimensions
 status = nf90_def_dim(ncid, "lat", 5, LatDimId)
 if(status /= nf90_NoErr) call handle_error(status)
 status = nf90_def_dim(ncid, "lon", 10, LonDimId)
 if(status /= nf90_NoErr) call handle_error(status)
 status = nf90_def_dim(ncid, "time", nf90_unlimited, TimeDimId)
 if(status /= nf90_NoErr) call handle_error(status)
 ...
 ! Define the variable
 status = nf90_def_var(ncid, "rh", nf90_double, &
                       (/ LonDimId, LatDimID, TimeDimID /), RhVarId)
 if(status /= nf90_NoErr) call handle_error(status)
@end example

In the following example, from nf_test/f90tst_vars2.f90, chunking,
checksums, and endianness control are all used in a netCDF-4/HDF5
file.

@example
  ! Create the netCDF file. 
  call check(nf90_create(FILE_NAME, nf90_netcdf4, ncid, cache_nelems = CACHE_NELEMS, &
       cache_size = CACHE_SIZE))

  ! Define the dimensions.
  call check(nf90_def_dim(ncid, "x", NX, x_dimid))
  call check(nf90_def_dim(ncid, "y", NY, y_dimid))
  dimids =  (/ y_dimid, x_dimid /)

  ! Define some variables. 
  chunksizes = (/ NY, NX /)
  call check(nf90_def_var(ncid, VAR1_NAME, NF90_INT, dimids, varid1, chunksizes = chunksizes, &
       shuffle = .TRUE., fletcher32 = .TRUE., endianness = nf90_endian_big, deflate_level = DEFLATE_LEVEL))
  call check(nf90_def_var(ncid, VAR2_NAME, NF90_INT, dimids, varid2, contiguous = .TRUE.))
  call check(nf90_def_var(ncid, VAR3_NAME, NF90_INT64, varid3))
  call check(nf90_def_var(ncid, VAR4_NAME, NF90_INT, x_dimid, varid4, contiguous = .TRUE.))
@end example

@node NF90_DEF_VAR_FILL, NF90_INQ_VAR_FILL, NF90_DEF_VAR, Variables
@section Define Fill Parameters for a Variable: @code{nf90_def_var_fill}
@findex NF90_DEF_VAR_FILL
@cindex fill
@cindex variables, fill

The function NF90_DEF_VAR_FILL sets the fill parameters for a
variable in a netCDF-4 file. 

This function must be called after the variable is defined, but before
NF90_ENDDEF is called.

@heading Usage 

@example
NF90_DEF_VAR_FILL(INTEGER NCID, INTEGER VARID, INTEGER NO_FILL, FILL_VALUE);
@end example

@table @code
@item NCID
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item VARID
Variable ID.

@item NO_FILL
Set to non-zero value to set no_fill mode on a variable. When this
mode is on, fill values will not be written for the variable. This is
helpful in high performance applications. For netCDF-4/HDF5 files
(whether classic model or not), this may only be changed after the
variable is defined, but before it is committed to disk (i.e. before
the first NF90_ENDDEF after the NF90_DEF_VAR.) For classic and 64-bit
offset file, the no_fill mode may be turned on and off at any time.

@item FILL_VALUE
A value which will be used as the fill value for the variable. Must be
the same type as the variable. This will be written to a _FillValue
attribute, created for this purpose. If NULL, this argument will be
ignored.
 
@end table

@heading Return Codes

@table @code

@item NF90_NOERR
No error.

@item NF90_BADID
Bad ncid.

@item NF90_ENOTNC4
Not a netCDF-4 file.

@item NF90_ENOTVAR
Can't find this variable.

@item NF90_ELATEDEF
This variable has already been the subject of a NF90_ENDDEF call. In
netCDF-4 files NF90_ENDDEF will be called automatically for any data
read or write. Once enddef has been called, it is impossible to set
the fill for a variable.

@item NF90_ENOTINDEFINE
Not in define mode. This is returned for netCDF classic or 64-bit
offset files, or for netCDF-4 files, when they were been created with
NF90_STRICT_NC3 flag. (@pxref{NF90_CREATE}).

@item NF90_EPERM
Attempt to create object in read-only file.

@end table

@heading Example

@example
@end example

@node NF90_INQ_VAR_FILL, NF90_INQUIRE_VARIABLE, NF90_DEF_VAR_FILL, Variables
@section Learn About Fill Parameters for a Variable: @code{NF90_INQ_VAR_FILL}
@findex NF90_INQ_VAR_FILL

The function NF90_INQ_VAR_FILL returns the fill settings for a
variable in a netCDF-4 file. 

@heading Usage 

@example
NF90_INQ_VAR_FILL(INTEGER NCID, INTEGER VARID, INTEGER NO_FILL, FILL_VALUE)
@end example

@table @code

@item NCID
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item VARID
Variable ID.

@item NO_FILL
An integer which will get a 1 if no_fill mode is set for this
variable, and a zero if it is not set

@item FILL_VALUE
This will get the fill value for this variable. This
parameter will be ignored if it is NULL.

@end table

@heading Return Codes

@table @code

@item NF90_NOERR
No error.

@item NF90_BADID
Bad ncid.

@item NF90_ENOTNC4
Not a netCDF-4 file.

@item NF90_ENOTVAR
Can't find this variable.

@end table

@heading Example

@example
@end example

@node NF90_INQUIRE_VARIABLE, NF90_INQ_VARID, NF90_INQ_VAR_FILL, Variables
@section Get Information about a Variable from Its ID: NF90_INQUIRE_VARIABLE
@findex NF90_INQUIRE_VARIABLE 
@cindex NF90_INQUIRE_VARIABLE , example

NF90_INQUIRE_VARIABLE returns information about a netCDF variable
given its ID. Information about a variable includes its name, type,
number of dimensions, a list of dimension IDs describing the shape of
the variable, and the number of variable attributes that have been
assigned to the variable.

All parameters after nAtts are optional, and only supported if netCDF
was built with netCDF-4 features enabled, and if the variable is in a
netCDF-4/HDF5 file.

@heading Usage 
@example
  function nf90_inquire_variable(ncid, varid, name, xtype, ndims, dimids, nAtts, &
       contiguous, chunksizes, deflate_level, shuffle, fletcher32, endianness)
    integer, intent(in) :: ncid, varid
    character (len = *), optional, intent(out) :: name
    integer, optional, intent(out) :: xtype, ndims 
    integer, dimension(:), optional, intent(out) :: dimids
    integer, optional, intent(out) :: nAtts
    logical, optional, intent(out) :: contiguous
    integer, optional, dimension(:), intent(out) :: chunksizes
    integer, optional, intent(out) :: deflate_level
    logical, optional, intent(out) :: shuffle, fletcher32
    integer, optional, intent(out) :: endianness
    integer :: nf90_inquire_variable
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item varid
Variable ID.
 
@item name
Returned variable name. The caller must allocate space for the
returned name. The maximum possible length, in characters, of a
variable name is given by the predefined constant NF90_MAX_NAME.
 
@item xtype
Returned variable type, one of the set of predefined netCDF external
data types. The type of this parameter, NF90_TYPE, is defined in the
netCDF header file. The valid netCDF external data types are NF90_BYTE,
NF90_CHAR, NF90_SHORT, NF90_INT, NF90_FLOAT, AND NF90_DOUBLE.
 
@item ndims
Returned number of dimensions the variable was defined as using. For
example, 2 indicates a matrix, 1 indicates a vector, and 0 means the
variable is a scalar with no dimensions.
 
@item dimids
Returned vector of *ndimsp dimension IDs corresponding to the
variable dimensions. The caller must allocate enough space for a
vector of at least *ndimsp integers to be returned. The maximum
possible number of dimensions for a variable is given by the
predefined constant NF90_MAX_VAR_DIMS.
 
@item natts
Returned number of variable attributes assigned to this variable.

@item contiguous
On return, set to NF90_CONTIGUOUS if this variable uses contiguous
storage, NF90_CHUNKED if it uses chunked storage.

@item chunksizes
An array of chunk sizes. The array must have the one element for
each dimension in the variable.

@item shuffle
True if the shuffle filter is turned on for this variable.

@item deflate_level
The deflate_level from 0 to 9. A value of zero indicates no deflation
is in use.

@item fletcher32
Set to true if the fletcher32 checksum filter is turned on for this
variable.
 
@item endianness
Will be set to NF90_ENDIAN_LITTLE if this variable is stored in
little-endian format, NF90_ENDIAN_BIG if it is stored in big-endian
format, and NF90_ENDIAN_NATIVE if the endianness is not set, and the
variable is not created yet.

@end table

These functions return the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The variable ID is invalid for the specified netCDF dataset. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@end itemize

@heading Example 

Here is an example using NF90_INQ_VAR to find out about a variable named
rh in an existing netCDF dataset named foo.nc:

@example
    use netcdf
    implicit none
    integer                            :: status, ncid, &
                                          RhVarId       &
                                          numDims, numAtts
 integer, dimension(nf90_max_var_dims) :: rhDimIds
 ...
 status = nf90_open("foo.nc", nf90_NoWrite, ncid)
 if(status /= nf90_NoErr) call handle_error(status)
 ...
 status = nf90_inq_varid(ncid, "rh", RhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_inquire_variable(ncid, RhVarId, ndims = numDims, natts = numAtts)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_inquire_variable(ncid, RhVarId, dimids = rhDimIds(:numDims))
 if(status /= nf90_NoErr) call handle_err(status)
@end example

@node NF90_INQ_VARID, NF90_PUT_VAR, NF90_INQUIRE_VARIABLE, Variables
@section Get the ID of a variable from the name: NF90_INQ_VARID
@findex NF90_INQ_VARID 
@cindex NF90_INQ_VARID, example

Given the name of a varaible, nf90_inq_varid finds the variable ID.

@heading Usage 
@example
  function nf90_inq_varid(ncid, name, varid)
    integer, intent(in) :: ncid
    character (len = *), intent( in) :: name
    integer, intent(out) :: varid
    integer :: nf90_inq_varid
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item name
The variable name. The maximum possible length, in characters, of a
variable name is given by the predefined constant NF90_MAX_NAME.
 
@item varid
Variable ID.
 
@end table

These functions return the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
Variable not found.

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@end itemize

@heading Example 

Here is an example using NF90_INQ_VARID to find out about a variable
named rh in an existing netCDF dataset named foo.nc:

@example
    use netcdf
    implicit none
    integer                            :: status, ncid, &
                                          RhVarId       &
                                          numDims, numAtts
 integer, dimension(nf90_max_var_dims) :: rhDimIds
 ...
 status = nf90_open("foo.nc", nf90_NoWrite, ncid)
 if(status /= nf90_NoErr) call handle_error(status)
 ...
 status = nf90_inq_varid(ncid, "rh", RhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_inquire_variable(ncid, RhVarId, ndims = numDims, natts = numAtts)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_inquire_variable(ncid, RhVarId, dimids = rhDimIds(:numDims))
 if(status /= nf90_NoErr) call handle_err(status)
@end example

@node NF90_PUT_VAR, NF90_GET_VAR, NF90_INQ_VARID, Variables
@section Writing Data Values: NF90_PUT_VAR
@findex NF90_PUT_VAR
@cindex NF90_PUT_VAR, example

The function NF90_PUT_VAR puts one or more data values into the
variable of an open netCDF dataset that is in data mode. Required
inputs are the netCDF ID, the variable ID, and one or more data
values. Optional inputs may indicate the starting position of the data
values in the netCDF variable (argument start), the sampling frequency
with which data values are written into the netCDF variable (argument
stride), and a mapping between the dimensions of the data array and
the netCDF variable (argument map). The values to be written are
associated with the netCDF variable by assuming that the first
dimension of the netCDF variable varies fastest in the Fortran 90
interface. Data values are converted to the external type of the variable,
if necessary.

Take care when using the simplest forms of this interface with record
variables (variables that use the NF90_UNLIMITED dimension) when you
don't specify how many records are to be written. If you try to write
all the values of a record variable into a netCDF file that has no
record data yet (hence has 0 records), nothing will be
written. Similarly, if you try to write all the values of a record
variable from an array but there are more records in the file than you
assume, more in-memory data will be accessed than you expect, which may
cause a segmentation violation.  To avoid such problems, it is better
to specify start and count arguments for variables that use the
NF90_UNLIMITED dimension.

@heading Usage 
@example
 function nf90_put_var(ncid, varid, values, start, count, stride, map)
   integer,                         intent( in) :: ncid, varid
   any valid type, scalar or array of any rank, &
                                    intent( in) :: values
   integer, dimension(:), optional, intent( in) :: start, count, stride, map
   integer                                      :: nf90_put_var
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item varid
Variable ID.
 
@item values
The data value(s) to be written. The data may be of any type, and may
be a scalar or an array of any rank.  You cannot put CHARACTER data
into a numeric variable or numeric data into a text variable. For
numeric data, if the type of data differs from the netCDF variable
type, type conversion will occur. @xref{Type Conversion,,, netcdf,
NetCDF Users Guide}.

@item start
A vector of integers specifying the index in the variable where the
first (or only) of the data values will be written. The indices are
relative to 1, so for example, the first data value of a variable
would have index (1, 1, ..., 1). The elements of start correspond, in
order, to the variable's dimensions. Hence, if the variable is a
record variable, the last index would correspond to the starting
record number for writing the data values.  

By default, start(:) = 1.

@item count
A vector of integers specifying the number of indices selected along
each dimension. To write a single value, for example, specify count as
(1, 1, ..., 1). The elements of count correspond, in order, to the
variable's dimensions. Hence, if the variable is a record variable,
the last element of count corresponds to a count of the number of
records to write.  

By default, count(:numDims) = shape(values) and
count(numDims + 1:) = 1, where numDims = size(shape(values)).

@item stride
A vector of integers that specifies the sampling interval along each
dimension of the netCDF variable. The elements of the stride vector
correspond, in order, to the netCDF variable's dimensions (stride(1)
gives the sampling interval along the most rapidly varying dimension
of the netCDF variable). Sampling intervals are specified in
type-independent units of elements (a value of 1 selects consecutive
elements of the netCDF variable along the corresponding dimension, a
value of 2 selects every other element, etc.).

By default, stride(:) = 1. 

@item imap
A vector of integers that specifies the mapping between the dimensions
of a netCDF variable and the in-memory structure of the internal data
array. The elements of the index mapping vector correspond, in order,
to the netCDF variable's dimensions (map(1) gives the distance between
elements of the internal array corresponding to the most rapidly
varying dimension of the netCDF variable). Distances between elements
are specified in units of elements.

By default, edgeLengths = shape(values), and 
map = (/ 1, (product(edgeLengths(:i)), i = 1, size(edgeLengths) - 1) /), 
that is, there is no mapping. 

Use of Fortran 90 intrinsic functions (including reshape, transpose,
and spread) may let you avoid using this argument. 
@end table

@heading Errors 

NF90_PUT_VAR1_  type returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The variable ID is invalid for the specified netCDF dataset.

@item
The specified indices were out of range for the rank of the specified
variable. For example, a negative index or an index that is larger
than the corresponding dimension length will cause an error.

@item
The specified value is out of the range of values representable by the
external data type of the variable.

@item
The specified netCDF is in define mode rather than data mode. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example 

Here is an example using NF90_PUT_VAR to set the (4,3,2) element of
the variable named rh to 0.5 in an existing netCDF dataset named
foo.nc. For simplicity in this example, we assume that we know that rh
is dimensioned with lon, lat, and time, so we want to set the value of
rh that corresponds to the fourth lon value, the third lat value, and
the second time value:

@example
 use netcdf
 implicit none
 integer :: ncId, rhVarId, status
 ...
 status = nf90_open("foo.nc", nf90_Write, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_put_var(ncid, rhVarId, 0.5, start = (/ 4, 3, 2 /) )
 if(status /= nf90_NoErr) call handle_err(status)
@end example

In this example we use NF90_PUT_VAR to add or change all the values of
the variable named rh to 0.5 in an existing netCDF dataset named
foo.nc. We assume that we know that rh is dimensioned with lon, lat,
and time. In this example we query the netCDF file to discover the
lengths of the dimensions, then use the Fortran 90 intrinsic function
reshape to create a temporary array of data values which is the same
shape as the netCDF variable.

@example
 use netcdf
 implicit none
 integer                               :: ncId, rhVarId,status,          &
                                          lonDimID, latDimId, timeDimId, &
                                          numLons, numLats, numTimes,    &
                                          i
 integer, dimension(nf90_max_var_dims) :: dimIDs
 ...
 status = nf90_open("foo.nc", nf90_Write, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 ! How big is the netCDF variable, that is, what are the lengths of 
 !   its constituent dimensions? 
 status = nf90_inquire_variable(ncid, rhVarId, dimids = dimIDs)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_inquire_dimension(ncid, dimIDs(1), len = numLons)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_inquire_dimension(ncid, dimIDs(2), len = numLats)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_inquire_dimension(ncid, dimIDs(3), len = numTimes)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 ! Make a temporary array the same shape as the netCDF variable. 
 status = nf90_put_var(ncid, rhVarId, &
                       reshape( &
                         (/ (0.5, i = 1, numLons * numLats * numTimes) /) , &
                        shape = (/ numLons, numLats, numTimes /) )
 if(status /= nf90_NoErr) call handle_err(status)
@end example

Here is an example using NF90_PUT_VAR to add or change a section of
the variable named rh to 0.5 in an existing netCDF dataset named
foo.nc. For simplicity in this example, we assume that we know that rh
is dimensioned with lon, lat, and time, that there are ten lon values,
five lat values, and three time values, and that we want to replace
all the values at the last time.

@example
 use netcdf
 implicit none
 integer            :: ncId, rhVarId, status
 integer, parameter :: numLons = 10, numLats = 5, numTimes = 3
 real, dimension(numLons, numLats) &
                    :: rhValues
 ...
 status = nf90_open("foo.nc", nf90_Write, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 ! Fill in all values at the last time
 rhValues(:, :) = 0.5
 status = nf90_put_var(ncid, rhVarId,rhvalues,       &
                       start = (/ 1, 1, numTimes /), &
                       count = (/ numLats, numLons, 1 /))
 if(status /= nf90_NoErr) call handle_err(status)
@end example

Here is an example of using NF90_PUT_VAR to write every other point of a
netCDF variable named rh having dimensions (6, 4).

@example
 use netcdf
 implicit none
 integer            :: ncId, rhVarId, status
 integer, parameter :: numLons = 6, numLats = 4
 real, dimension(numLons, numLats) &
                    :: rhValues = 0.5
 ...
 status = nf90_open("foo.nc", nf90_Write, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 ! Fill in every other value using an array section 
 status = nf90_put_var(ncid, rhVarId, rhValues(::2, ::2), &
                       stride = (/ 2, 2 /))
 if(status /= nf90_NoErr) call handle_err(status)
@end example

The following map vector shows the default mapping between a 2x3x4
netCDF variable and an internal array of the same shape:

@example
 real,    dimension(2, 3, 4):: a  ! same shape as netCDF variable
 integer, dimension(3)      :: map  = (/ 1, 2, 6 /) 
                     ! netCDF dimension inter-element distance
                     ! ---------------- ----------------------
                     ! most rapidly varying       1
                     ! intermediate               2 (= map(1)*2)
                     ! most slowly varying        6 (= map(2)*3)
@end example

Using the map vector above obtains the same result as simply not passing a map vector at all. 

Here is an example of using nf90_put_var to write a netCDF variable
named rh whose dimensions are the transpose of the Fortran 90 array:

@example
 use netcdf
 implicit none
 integer                           :: ncId, rhVarId, status
 integer, parameter                :: numLons = 6, numLats = 4
 real, dimension(numLons, numLats) :: rhValues
 ! netCDF variable has dimensions (numLats, numLons)
 ...
 status = nf90_open("foo.nc", nf90_Write, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 !Write transposed values: map vector would be (/ 1, numLats /) for 
 !   no transposition
 status = nf90_put_var(ncid, rhVarId,rhValues, map = (/ numLons, 1 /)) 
 if(status /= nf90_NoErr) call handle_err(status)
@end example

The same effect can be obtained more simply using Fortran 90 intrinsic functions: 

@example
 use netcdf
 implicit none
 integer                           :: ncId, rhVarId, status
 integer, parameter                :: numLons = 6, numLats = 4
 real, dimension(numLons, numLats) :: rhValues
 ! netCDF variable has dimensions (numLats, numLons)
 ...
 status = nf90_open("foo.nc", nf90_Write, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_put_var(ncid, rhVarId, transpose(rhValues)) 
 if(status /= nf90_NoErr) call handle_err(status)
@end example

@node NF90_GET_VAR, Reading and Writing Character String Values, NF90_PUT_VAR, Variables
@section Reading Data Values: NF90_GET_VAR
@findex NF90_GET_VAR
@cindex NF90_GET_VAR, example

The function NF90_GET_VAR gets one or more data values from a netCDF
variable of an open netCDF dataset that is in data mode. Required
inputs are the netCDF ID, the variable ID, and a specification for the
data values into which the data will be read. Optional inputs may
indicate the starting position of the data values in the netCDF
variable (argument start), the sampling frequency with which data
values are read from the netCDF variable (argument stride), and a
mapping between the dimensions of the data array and the netCDF
variable (argument map). The values to be read are associated with the
netCDF variable by assuming that the first dimension of the netCDF
variable varies fastest in the Fortran 90 interface. Data values are
converted from the external type of the variable, if necessary.

Take care when using the simplest forms of this interface with record
variables (variables that use the NF90_UNLIMITED dimension) when you
don't specify how many records are to be read. If you try to read all
the values of a record variable into an array but there are more
records in the file than you assume, more data will be read than you
expect, which may cause a segmentation violation.  To avoid such
problems, it is better to specify the optional start and count
arguments for variables that use the NF90_UNLIMITED dimension.

In netCDF classic model the maximum integer size is NF90_INT, the
4-byte signed integer. Reading variables into an eight-byte integer
array from a classic model file will read from an NF90_INT. Reading
variables into an eight-byte integer in a netCDF-4/HDF5 (without
classic model flag) will read from an NF90_INT64

@heading Usage 
@example
 function nf90_get_var(ncid, varid, values, start, count, stride, map)
   integer,                         intent( in) :: ncid, varid
   any valid type, scalar or array of any rank, &
                                    intent(out) :: values
   integer, dimension(:), optional, intent( in) :: start, count, stride, map
   integer                                      :: nf90_get_var
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item varid
Variable ID.
 
@item values
The data value(s) to be read. The data may be of any type, and may be
a scalar or an array of any rank.  You cannot read CHARACTER data from
a numeric variable or numeric data from a text variable. For numeric
data, if the type of data differs from the netCDF variable type, type
conversion will occur. @xref{Type Conversion,,, netcdf, NetCDF Users
Guide}.

@item start
A vector of integers specifying the index in the variable from which
the first (or only) of the data values will be read. The indices are
relative to 1, so for example, the first data value of a variable
would have index (1, 1, ..., 1). The elements of start correspond, in
order, to the variable's dimensions. Hence, if the variable is a
record variable, the last index would correspond to the starting
record number for writing the data values.

By default, start(:) = 1. 

@item count
A vector of integers specifying the number of indices selected along
each dimension. To read a single value, for example, specify count as
(1, 1, ..., 1). The elements of count correspond, in order, to the
variable's dimensions. Hence, if the variable is a record variable,
the last element of count corresponds to a count of the number of
records to read.

By default, count(:numDims) = shape(values) and 
count(numDims + 1:) = 1, where numDims = size(shape(values)).

@item stride
A vector of integers that specifies the sampling interval along each
dimension of the netCDF variable. The elements of the stride vector
correspond, in order, to the netCDF variable's dimensions (stride(1)
gives the sampling interval along the most rapidly varying dimension
of the netCDF variable). Sampling intervals are specified in
type-independent units of elements (a value of 1 selects consecutive
elements of the netCDF variable along the corresponding dimension, a
value of 2 selects every other element, etc.).

By default, stride(:) = 1. 

@item map
A vector of integers that specifies the mapping between the dimensions
of a netCDF variable and the in-memory structure of the internal data
array. The elements of the index mapping vector correspond, in order,
to the netCDF variable's dimensions (map(1) gives the distance between
elements of the internal array corresponding to the most rapidly
varying dimension of the netCDF variable). Distances between elements
are specified in units of elements.

By default, edgeLengths = shape(values), and 
map = (/ 1, (product(edgeLengths(:i)), i = 1, size(edgeLengths) - 1) /), 
that is, there is no mapping. 

Use of Fortran 90 intrinsic functions (including reshape, transpose,
and spread) may let you avoid using this argument.

@end table

@heading Errors 

NF90_GET_VAR returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The variable ID is invalid for the specified netCDF dataset. 

@item
The assumed or specified start, count, and stride generate an index
which is out of range. Note that no error checking is possible on the
map vector.

@item
One or more of the specified values are out of the range of values
representable by the desired type.

@item
The specified netCDF is in define mode rather than data mode. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

(As noted above, another possible source of error is using this
interface to read all the values of a record variable without
specifying the number of records. If there are more records in the
file than you assume, more data will be read than you expect!)

@heading Example 

Here is an example using NF90_GET_VAR to read the (4,3,2) element of
the variable named rh from an existing netCDF dataset named
foo.nc. For simplicity in this example, we assume that we know that rh
is dimensioned with lon, lat, and time, so we want to read the value
of rh that corresponds to the fourth lon value, the third lat value,
and the second time value:

@example
 use netcdf
 implicit none
 integer :: ncId, rhVarId, status
 real    :: rhValue
 ...
 status = nf90_open("foo.nc", nf90_NoWrite, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 -
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_get_var(ncid, rhVarId, rhValue, start = (/ 4, 3, 2 /) )
 if(status /= nf90_NoErr) call handle_err(status)
@end example

In this example we use NF90_GET_VAR to read all the values of the
variable named rh from an existing netCDF dataset named foo.nc. We
assume that we know that rh is dimensioned with lon, lat, and time. In
this example we query the netCDF file to discover the lengths of the
dimensions, then allocate a Fortran 90 array the same shape as the
netCDF variable.

@example
 use netcdf
 implicit none
 integer                               :: ncId, rhVarId, &
                                          lonDimID, latDimId, timeDimId, &
                                          numLons, numLats, numTimes,    &
                                          status
 integer, dimension(nf90_max_var_dims) :: dimIDs
 real, dimension(:, :, :), allocatable :: rhValues
 ...
 status = nf90_open("foo.nc", nf90_NoWrite, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 ! How big is the netCDF variable, that is, what are the lengths of 
 !   its constituent dimensions? 
 status = nf90_inquire_variable(ncid, rhVarId, dimids = dimIDs)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_inquire_dimension(ncid, dimIDs(1), len = numLons)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_inquire_dimension(ncid, dimIDs(2), len = numLats)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_inquire_dimension(ncid, dimIDs(3), len = numTimes)
 if(status /= nf90_NoErr) call handle_err(status)
 allocate(rhValues(numLons, numLats, numTimes))
 ...
 status = nf90_get_var(ncid, rhVarId, rhValues)
 if(status /= nf90_NoErr) call handle_err(status)
@end example

Here is an example using NF90_GET_VAR to read a section of the
variable named rh from an existing netCDF dataset named foo.nc. For
simplicity in this example, we assume that we know that rh is
dimensioned with lon, lat, and time, that there are ten lon values,
five lat values, and three time values, and that we want to replace
all the values at the last time.

@example
 use netcdf
 implicit none
 integer            :: ncId, rhVarId, status
 integer, parameter :: numLons = 10, numLats = 5, numTimes = 3
 real, dimension(numLons, numLats, numTimes) &
                    :: rhValues
 ...
 status = nf90_open("foo.nc", nf90_NoWrite, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 !Read the values at the last time by passing an array section 
 status = nf90_get_var(ncid, rhVarId, rhValues(:, :, 3), &
                       start = (/ 1, 1, numTimes /),     &
                       count = (/ numLons, numLats, 1 /))
 if(status /= nf90_NoErr) call handle_err(status)
@end example

Here is an example of using NF90_GET_VAR to read every other point of a
netCDF variable named rh having dimensions (6, 4).

@example
 use netcdf
 implicit none
 integer            :: ncId, rhVarId, status
 integer, parameter :: numLons = 6, numLats = 4
 real, dimension(numLons, numLats) &
                    :: rhValues
 ...
 status = nf90_open("foo.nc", nf90_NoWrite, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 ! Read every other value into an array section 
 status = nf90_get_var(ncid, rhVarId, rhValues(::2, ::2) &
                       stride = (/ 2, 2 /))
 if(status /= nf90_NoErr) call handle_err(status)
@end example

The following map vector shows the default mapping between a 2x3x4
netCDF variable and an internal array of the same shape:

@example
 real,    dimension(2, 3, 4):: a  ! same shape as netCDF variable
 integer, dimension(3)      :: map  = (/ 1, 2, 6 /) 
                     ! netCDF dimension inter-element distance
                     ! ---------------- ----------------------
                     ! most rapidly varying       1
                     ! intermediate               2 (= map(1)*2)
                     ! most slowly varying        6 (= map(2)*3)
@end example

Using the map vector above obtains the same result as simply not
passing a map vector at all.

Here is an example of using nf90_get_var to read a netCDF variable
named rh whose dimensions are the transpose of the Fortran 90 array:

@example
 use netcdf
 implicit none
 integer                           :: ncId, rhVarId, status
 integer, parameter                :: numLons = 6, numLats = 4
 real, dimension(numLons, numLats) :: rhValues
 ! netCDF variable has dimensions (numLats, numLons)
 ...
 status = nf90_open("foo.nc", nf90_NoWrite, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 ! Read transposed values: map vector would be (/ 1, numLats /) for 
 !   no transposition
 status = nf90_get_var(ncid, rhVarId,rhValues, map = (/ numLons, 1 /)) 
 if(status /= nf90_NoErr) call handle_err(status)
@end example

The same effect can be obtained more simply, though using more memory,
using Fortran 90 intrinsic functions:

@example
 use netcdf
 implicit none
 integer                           :: ncId, rhVarId, status
 integer, parameter                :: numLons = 6, numLats = 4
 real, dimension(numLons, numLats) :: rhValues
 ! netCDF variable has dimensions (numLats, numLons)
 real, dimension(numLons, numLats) :: tempValues
 ...
 status = nf90_open("foo.nc", nf90_NoWrite, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_get_var(ncid, rhVarId, tempValues)) 
 if(status /= nf90_NoErr) call handle_err(status)
 rhValues(:, :) = transpose(tempValues)
@end example

@node Reading and Writing Character String Values, Fill Values, NF90_GET_VAR, Variables
@section Reading and Writing Character String Values

Character strings are not a primitive netCDF external data type under
the classic netCDF data model, in
part because Fortran does not support the abstraction of
variable-length character strings (the Fortran LEN function returns
the static length of a character string, not its dynamic length). As a
result, a character string cannot be written or read as a single
object in the netCDF interface. Instead, a character string must be
treated as an array of characters, and array access must be used to
read and write character strings as variable data in netCDF
datasets. Furthermore, variable-length strings are not supported by
the netCDF classic interface except by convention; for example, you may treat
a zero byte as terminating a character string, but you must explicitly
specify the length of strings to be read from and written to netCDF
variables.

Character strings as attribute values are easier to use, since the
strings are treated as a single unit for access. However, the value of
a character-string attribute in the classic netCDF interface is still
an array of characters with an
explicit length that must be specified when the attribute is defined.

When you define a variable that will have character-string values, use
a character-position dimension as the most quickly varying dimension
for the variable (the first dimension for the variable in Fortran
90). The length of the character-position dimension will be the
maximum string length of any value to be stored in the
character-string variable. Space for maximum-length strings will be
allocated in the disk representation of character-string variables
whether you use the space or not. If two or more variables have the
same maximum length, the same character-position dimension may be used
in defining the variable shapes.

To write a character-string value into a character-string variable,
use either entire variable access or array access. The latter requires
that you specify both a corner and a vector of edge lengths. The
character-position dimension at the corner should be one for Fortran
90. If the length of the string to be written is n, then the vector of
edge lengths will specify n in the character-position dimension, and
one for all the other dimensions: (n, 1, 1, ..., 1).

In Fortran 90, fixed-length strings may be written to a netCDF dataset
without a terminating character, to save space. Variable-length
strings should follow the C convention of writing strings with a
terminating zero byte so that the intended length of the string can be
determined when it is later read by either C or Fortran 90 programs.
It is the users responsibility to provide such null termination.

If you are writing data in the default prefill mode (see next section),
you can ensure that simple strings represented as 1-dimensional
character arrays are null terminated in the netCDF file by writing fewer
characters than the length declared when the variable was defined.
That way, the extra unwritten characters will be filled with the
default character fill value, which is a null byte.  The Fortran
intrinsic TRIM function can be used to trim trailing blanks from the
character string argument to NF90_PUT_VAR to make the argument shorter
than the declared length.  If prefill is not on, the data writer must
explicitly provide a null terminating byte.

Here is an example illustrating this way of writing strings to
character array variables:

@example
 use netcdf
 implicit none
 integer status
 integer                           :: ncid, oceanStrLenID, oceanId
 integer, parameter                :: MaxOceanNameLen = 20
 character, (len = MaxOceanNameLen):: ocean
 ...
 status = nf90_create("foo.nc", nf90_NoClobber, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_def_dim(ncid, "oceanStrLen", MaxOceanNameLen, oceanStrLenId)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_def_var(ncid, "ocean", nf90_char, (/ oceanStrLenId /), oceanId)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 ! Leave define mode, which prefills netCDF variables with fill values
 status = nf90_enddef(ncid)
 if (status /= nf90_noerr) call handle_err(status)
 ...
 ! Note that this assignment adds blank fill
 ocean = "Pacific"
 ! Using trim removes trailing blanks, prefill provides null
 ! termination, so C programs can later get intended string.
 status = nf90_put_var(ncid, oceanId, trim(ocean)) 
 if(status /= nf90_NoErr) call handle_err(status)
@end example

@node Fill Values, NF90_RENAME_VAR, Reading and Writing Character String Values, Variables
@section Fill Values

What happens when you try to read a value that was never written in an
open netCDF dataset? You might expect that this should always be an
error, and that you should get an error message or an error status
returned. You do get an error if you try to read data from a netCDF
dataset that is not open for reading, if the variable ID is invalid
for the specified netCDF dataset, or if the specified indices are not
properly within the range defined by the dimension lengths of the
specified variable. Otherwise, reading a value that was not written
returns a special fill value used to fill in any undefined values when
a netCDF variable is first written.

You may ignore fill values and use the entire range of a netCDF
external data type, but in this case you should make sure you write
all data values before reading them. If you know you will be writing
all the data before reading it, you can specify that no prefilling of
variables with fill values will occur by calling writing. This may
provide a significant performance gain for netCDF writes.

The variable attribute _FillValue may be used to specify the fill
value for a variable. There are default fill values for each type,
defined in module netcdf: NF90_FILL_CHAR, NF90_FILL_INT1 (same as
NF90_FILL_BYTE), NF90_FILL_INT2 (same as NF90_FILL_SHORT),
NF90_FILL_INT, NF90_FILL_REAL (same as NF90_FILL_FLOAT), and
NF90_FILL_DOUBLE

The netCDF byte and character types have different default fill
values. The default fill value for characters is the zero byte, a
useful value for detecting the end of variable-length C character
strings. If you need a fill value for a byte variable, it is
recommended that you explicitly define an appropriate _FillValue
attribute, as generic utilities such as ncdump will not assume a
default fill value for byte variables.

Type conversion for fill values is identical to type conversion for
other values: attempting to convert a value from one type to another
type that can't represent the value results in a range error. Such
errors may occur on writing or reading values from a larger type (such
as double) to a smaller type (such as float), if the fill value for
the larger type cannot be represented in the smaller type.

@node NF90_RENAME_VAR, NF90_VAR_PAR_ACCESS, Fill Values, Variables
@section NF90_RENAME_VAR 
@findex NF90_RENAME_VAR 
@cindex NF90_RENAME_VAR , example

The function NF90_RENAME_VAR changes the name of a netCDF variable in an
open netCDF dataset. If the new name is longer than the old name, the
netCDF dataset must be in define mode. You cannot rename a variable to
have the name of any existing variable.

@heading Usage 
@example
 function nf90_rename_var(ncid, varid, newname)
   integer,             intent( in) :: ncid, varid
   character (len = *), intent( in) :: newname
   integer                          :: nf90_rename_var
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item varid
Variable ID.
 
@item newname
New name for the specified variable.
@end table
 
@heading Errors 

NF90_RENAME_VAR returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize
@item
The new name is in use as the name of another variable. 

@item
The variable ID is invalid for the specified netCDF dataset. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example 

Here is an example using NF90_RENAME_VAR to rename the variable rh to
rel_hum in an existing netCDF dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncId, rhVarId, status
 ...
 status = nf90_open("foo.nc", nf90_Write, ncid)
 if(status /= nf90_NoErr) call handle_err(status)
 ...
 status = nf90_inq_varid(ncid, "rh", rhVarId)
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_redef(ncid)  ! Enter define mode to change variable name
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_rename_var(ncid, rhVarId, "rel_hum")
 if(status /= nf90_NoErr) call handle_err(status)
 status = nf90_enddef(ncid) ! Leave define mode
 if(status /= nf90_NoErr) call handle_err(status)
@end example

@node NF90_VAR_PAR_ACCESS,  , NF90_RENAME_VAR, Variables
@section Change between Collective and Independent Parallel Access: NF90_VAR_PAR_ACCESS
@findex NF90_VAR_PAR_ACCESS
@cindex NF90_VAR_PAR_ACCESS, example

The function NF90_VAR_PAR_ACCESS changes whether read/write operations
on a parallel file system are performed collectively or independently
(the default) on the variable. This function can only be called if the
file was created (see @ref{NF90_CREATE}) or opened (see
@ref{NF90_OPEN}) for parallel I/O.

This function is only available if the netCDF library was built with
parallel I/O enabled.

Calling this function affects only the open file - information about
whether a variable is to be accessed collectively or independently is
not written to the data file. Every time you open a file on a parallel
file system, all variables default to independent operations. The
change of a variable to collective access lasts only as long as that
file is open.

The variable can be changed from collective to independent, and back,
as often as desired.

Classic and 64-bit offset files, when opened for parallel access, use
the parallel-netcdf (a.k.a. pnetcdf) library, which does not allow
per-variable changes of access mode - the entire file must be access
independently or collectively. For classic and 64-bit offset files,
the nf90_var_par_access function changes the access for all variables
in the file.

@heading Usage 

@example
  function nf90_var_par_access(ncid, varid, access)
    integer, intent(in) :: ncid
    integer, intent(in) :: varid
    integer, intent(in) :: access
    integer :: nf90_var_par_access
  end function nf90_var_par_access
@end example

@table @code

@item ncid
NetCDF ID, from a previous call to NF90_OPEN (see @ref{NF90_OPEN}) or
NF90_CREATE (see @ref{NF90_CREATE}).
 
@item varid
Variable ID.
 
@item access
NF90_INDEPENDENT to set this variable to independent
operations. NF90_COLLECTIVE to set it to collective operations.

@end table
 
@heading Return Values

@table @code

@item NF90_NOERR
No error.

@item NF90_ENOTVAR
No variable found.

@item NF90_NOPAR
File not opened for parallel access.

@end table

@heading Example
This example comes from test program nf_test/f90tst_parallel.f90. For
this test to be run, netCDF must have been built with a
parallel-enabled HDF5, and --enable-parallel-tests must have been used
when configuring netcdf.

@example
  ! Reopen the file.
  call handle_err(nf90_open(FILE_NAME, nf90_nowrite, ncid, comm = MPI_COMM_WORLD, &
       info = MPI_INFO_NULL))

  ! Set collective access on this variable. This will cause all
  ! reads/writes to happen together on every processor.
  call handle_err(nf90_var_par_access(ncid, varid, nf90_collective))
      
  ! Read this processor's data.
  call handle_err(nf90_get_var(ncid, varid, data_in, start = start, count = count))
@end example

@node Attributes, Summary of Fortran 90 Interface, Variables, Top
@chapter Attributes

@menu
* Attributes Introduction::     
* NF90_PUT_ATT::                
* NF90_INQUIRE_ATTRIBUTE::      
* NF90_GET_ATT::                
* NF90_COPY_ATT::               
* NF90_RENAME_ATT::             
* NF90_DEL_ATT::                
@end menu

@node Attributes Introduction, NF90_PUT_ATT, Attributes, Attributes
@section Attributes Introduction

Attributes may be associated with each netCDF variable to specify such
properties as units, special values, maximum and minimum valid values,
scaling factors, and offsets. Attributes for a netCDF dataset are
defined when the dataset is first created, while the netCDF dataset is
in define mode. Additional attributes may be added later by reentering
define mode. A netCDF attribute has a netCDF variable to which it is
assigned, a name, a type, a length, and a sequence of one or more
values. An attribute is designated by its variable ID and name. When
an attribute name is not known, it may be designated by its variable
ID and number in order to determine its name, using the function
NF90_INQ_ATTNAME.

The attributes associated with a variable are typically defined
immediately after the variable is created, while still in define
mode. The data type, length, and value of an attribute may be changed
even when in data mode, as long as the changed attribute requires no
more space than the attribute as originally defined.

It is also possible to have attributes that are not associated with
any variable. These are called global attributes and are identified by
using NF90_GLOBAL as a variable pseudo-ID. Global attributes are
usually related to the netCDF dataset as a whole and may be used for
purposes such as providing a title or processing history for a netCDF
dataset.

Attributes are much more useful when they follow established community
conventions. @xref{Attribute Conventions,,,netcdf, @value{n-man}}.

Operations supported on attributes are: 

@itemize

@item
Create an attribute, given its variable ID, name, data type, length, and value. 

@item
Get attribute's data type and length from its variable ID and name. 

@item
Get attribute's value from its variable ID and name. 

@item
Copy attribute from one netCDF variable to another. 

@item
Get name of attribute from its number. 

@item
Rename an attribute. 

@item
Delete an attribute. 
@end itemize

@node NF90_PUT_ATT, NF90_INQUIRE_ATTRIBUTE, Attributes Introduction, Attributes
@section Create an Attribute: NF90_PUT_ATT
@findex NF90_PUT_ATT
@cindex NF90_PUT_ATT, example

The function NF90_PUT_ATTadds or changes a variable attribute or
global attribute of an open netCDF dataset. If this attribute is new,
or if the space required to store the attribute is greater than
before, the netCDF dataset must be in define mode.

@heading Usage 

Although it's possible to create attributes of all types, text and
double attributes are adequate for most purposes.

@example
 function nf90_put_att(ncid, varid, name, values)
   integer,            intent( in) :: ncid, varid
   character(len = *), intent( in) :: name
   any valid type, scalar or array of rank 1, &
                       intent( in) :: values
   integer                         :: nf90_put_att
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item varid
Variable ID of the variable to which the attribute will be assigned or
NF90_GLOBAL for a global attribute.
 
@item name
Attribute name.  Attribute name conventions are assumed by some netCDF
generic applications, e.g., @samp{units} as the name for a string
attribute that gives the units for a netCDF variable. @xref{Attribute
Conventions,,,netcdf, @value{n-man}}.
 
@item values
An array of attribute values. Values may be supplied as scalars or as
arrays of rank one (one dimensional vectors). The external data type
of the attribute is set to match the internal representation of the
argument, that is if values is a two byte integer array, the attribute
will be of type NF90_INT2. Fortran 90 intrinsic functions can be used
to convert attributes to the desired type.

@end table
 
@heading Errors 

NF90_PUT_ATT returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The variable ID is invalid for the specified netCDF dataset. 

@item
The specified netCDF type is invalid. 

@item
The specified length is negative. 

@item
The specified open netCDF dataset is in data mode and the specified
attribute would expand.

@item
The specified open netCDF dataset is in data mode and the specified
attribute does not already exist.

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@item
The number of attributes for this variable exceeds NF90_MAX_ATTRS. 

@end itemize

@heading Example 

Here is an example using NF90_PUT_ATT to add a variable attribute
named valid_range for a netCDF variable named rh and a global
attribute named title to an existing netCDF dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid, status, RHVarID
 ...
 status = nf90_open("foo.nc", nf90_write, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 ! Enter define mode so we can add the attribute
 status = nf90_redef(ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ! Get the variable ID for "rh"...
 status = nf90_inq_varid(ncid, "rh", RHVarID)
 if (status /= nf90_noerr) call handle_err(status)
 ! ...  put the range attribute, setting it to eight byte reals... 
 status = nf90_put_att(ncid, RHVarID, "valid_range", real((/ 0, 100 /))
 ! ... and the title attribute. 
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_put_att(ncid, RHVarID, "title", "example netCDF dataset") )
 if (status /= nf90_noerr) call handle_err(status)
 ! Leave define mode
 status = nf90_enddef(ncid)
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_INQUIRE_ATTRIBUTE, NF90_GET_ATT, NF90_PUT_ATT, Attributes
@section Get Information about an Attribute: NF90_INQUIRE_ATTRIBUTE and NF90_INQ_ATTNAME
@findex NF90_INQUIRE_ATTRIBUTE
@cindex NF90_INQUIRE_ATTRIBUTE, example
@findex NF90_INQ_ATTNAME
@cindex NF90_INQ_ATTNAME, example

The function NF90_INQUIRE_ATTRIBUTE returns information about a netCDF
attribute given the variable ID and attribute name. Information about
an attribute includes its type, length, name, and number. See
NF90_GET_ATT for getting attribute values.

The function NF90_INQ_ATTNAME gets the name of an attribute, given its
variable ID and number. This function is useful in generic
applications that need to get the names of all the attributes
associated with a variable, since attributes are accessed by name
rather than number in all other attribute functions. The number of an
attribute is more volatile than the name, since it can change when
other attributes of the same variable are deleted. This is why an
attribute number is not called an attribute ID.

@heading Usage 
@example
 function nf90_inquire_attribute(ncid, varid, name, xtype, len, attnum)
   integer,             intent( in)           :: ncid, varid
   character (len = *), intent( in)           :: name
   integer,             intent(out), optional :: xtype, len, attnum
   integer                                    :: nf90_inquire_attribute
 function nf90_inq_attname(ncid, varid, attnum, name)
   integer,             intent( in) :: ncid, varid, attnum
   character (len = *), intent(out) :: name
   integer                          :: nf90_inq_attname
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item varid
Variable ID of the attribute's variable, or NF90_GLOBAL for a global
attribute.
 
@item name
Attribute name. For NF90_INQ_ATTNAME, this is a pointer to the location
for the returned attribute name.
 
@item xtype
Returned attribute type, one of the set of predefined netCDF external
data types. The valid netCDF external data types are NF90_BYTE, NF90_CHAR,
NF90_SHORT, NF90_INT, NF90_FLOAT, and NF90_DOUBLE.
 
@item len
Returned number of values currently stored in the attribute. For a
string-valued attribute, this is the number of characters in the
string.
 
@item attnum
For NF90_INQ_ATTNAME, the input attribute number; for NF90_INQ_ATTID, the
returned attribute number. The attributes for each variable are
numbered from 1 (the first attribute) to NATTS, where NATTS is the
number of attributes for the variable, as returned from a call to
NF90_INQ_VARNATTS.

(If you already know an attribute name, knowing its number is not very
useful, because accessing information about an attribute requires its
name.)
@end table

@heading Errors 

Each function returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:
@itemize

@item
The variable ID is invalid for the specified netCDF dataset. 

@item
The specified attribute does not exist. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@item
For NF90_INQ_ATTNAME, the specified attribute number is negative or more
than the number of attributes defined for the specified variable.
@end itemize

@heading Example 

Here is an example using NF90_INQUIRE_ATTRIBUTE to inquire about the lengths
of an attribute named valid_range for a netCDF variable named rh and a
global attribute named title in an existing netCDF dataset named
foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid, status
 integer :: RHVarID                       ! Variable ID
 integer :: validRangeLength, titleLength ! Attribute lengths
 ... 
 status = nf90_open("foo.nc", nf90_nowrite, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ...  
 ! Get the variable ID for "rh"...
 status = nf90_inq_varid(ncid, "rh", RHVarID)
 if (status /= nf90_noerr) call handle_err(status)
 ! ...  get the length of the "valid_range" attribute... 
 status = nf90_inquire_attribute(ncid, RHVarID, "valid_range", &
                           len = validRangeLength)
 if (status /= nf90_noerr) call handle_err(status)
 ! ... and the global title attribute. 
 status = nf90_inquire_attribute(ncid, nf90_global, "title", len = titleLength)
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_GET_ATT, NF90_COPY_ATT, NF90_INQUIRE_ATTRIBUTE, Attributes
@section Get Attribute's Values: NF90_GET_ATT
@findex NF90_GET_ATT
@cindex NF90_GET_ATT, example

Function nf90_get_att gets the value(s) of a netCDF attribute, given
its variable ID and name.

@heading Usage 
@example
 function nf90_get_att(ncid, varid, name, values)
   integer,            intent( in) :: ncid, varid
   character(len = *), intent( in) :: name
   any valid type, scalar or array of rank 1, &
                       intent(out) :: values
   integer                         :: nf90_get_att
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item varid
Variable ID of the attribute's variable, or NF90_GLOBAL for a global attribute.
 
@item name
Attribute name.
 
@item values
Returned attribute values. All elements of the vector of attribute
values are returned, so you must provide enough space to hold them. If
you don't know how much space to reserve, call NF90_INQUIRE_ATTRIBUTE first
to find out the length of the attribute. If there is only a single
attribute values may be a scalar. If the attribute is of type
character values should be a variable of type character with the len
Fortran 90 attribute set to an appropriate value (i.e. character (len
= 80) :: values). You cannot read character data from a numeric
variable or numeric data from a text variable. For numeric data, if
the type of data differs from the netCDF variable type, type
conversion will occur. @xref{Type Conversion,,, netcdf, NetCDF Users
Guide}.

@end table
 
@heading Errors 

NF90_GET_ATT_ type returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:
@itemize

@item
The variable ID is invalid for the specified netCDF dataset. 

@item
The specified attribute does not exist. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@item
One or more of the attribute values are out of the range of values
representable by the desired type.
@end itemize

@heading Example 

Here is an example using NF90_GET_ATT to determine the values of an
attribute named valid_range for a netCDF variable named rh and a
global attribute named title in an existing netCDF dataset named
foo.nc. In this example, it is assumed that we don't know how many
values will be returned, so we first inquire about the length of the
attributes to make sure we have enough space to store them:

@example
 use netcdf
 implicit none
 integer              :: ncid, status
 integer              :: RHVarID                       ! Variable ID
 integer              :: validRangeLength, titleLength ! Attribute lengths
 real, dimension(:), allocatable, &
                      :: validRange
 character (len = 80) :: title                          
 ... 
 status = nf90_open("foo.nc", nf90_nowrite, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ... 
 ! Find the lengths of the attributes
 status = nf90_inq_varid(ncid, "rh", RHVarID)
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_inquire_attribute(ncid, RHVarID, "valid_range", &
                           len = validRangeLength)
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_inquire_attribute(ncid, nf90_global, "title", len = titleLength)
 if (status /= nf90_noerr) call handle_err(status)
 ... 
 !Allocate space to hold attribute values, check string lengths
 allocate(validRange(validRangeLength), stat = status)
 if(status /= 0 .or. len(title) < titleLength)
   print *, "Not enough space to put attribute values."
   exit
 end if
 ! Read the attributes. 
 status = nf90_get_att(ncid, RHVarID, "valid_range", validRange)
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_get_att(ncid, nf90_global, "title", title)
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_COPY_ATT, NF90_RENAME_ATT, NF90_GET_ATT, Attributes
@section Copy Attribute from One NetCDF to Another: NF90_COPY_ATT
@findex NF90_COPY_ATT
@cindex NF90_COPY_ATT, example

The function NF90_COPY_ATT copies an attribute from one open netCDF
dataset to another. It can also be used to copy an attribute from one
variable to another within the same netCDF dataset.

If used to copy an attribute of user-defined type, then that
user-defined type must already be defined in the target file. In the
case of user-defined attributes, enddef/redef is called for 
ncid_in and ncid_out if they are in define mode. (This is the ensure
that all user-defined types are committed to the file(s) before the
copy is attempted.)

@heading Usage 
@example
 function nf90_copy_att(ncid_in, varid_in, name, ncid_out, varid_out)
   integer,             intent( in) :: ncid_in,  varid_in
   character (len = *), intent( in) :: name
   integer,             intent( in) :: ncid_out, varid_out
   integer                          :: nf90_copy_att
@end example

@table @code
@item ncid_in
The netCDF ID of an input netCDF dataset from which the attribute
will be copied, from a previous call to NF90_OPEN or NF90_CREATE.
 
@item varid_in
ID of the variable in the input netCDF dataset from which the
attribute will be copied, or NF90_GLOBAL for a global attribute.
 
@item name
Name of the attribute in the input netCDF dataset to be copied.
 
@item ncid_out
The netCDF ID of the output netCDF dataset to which the attribute
will be copied, from a previous call to NF90_OPEN or NF90_CREATE. It is
permissible for the input and output netCDF IDs to be the same. The
output netCDF dataset should be in define mode if the attribute to be
copied does not already exist for the target variable, or if it would
cause an existing target attribute to grow.
 
@item varid_out
ID of the variable in the output netCDF dataset to which the
attribute will be copied, or NF90_GLOBAL to copy to a global attribute.
@end table
 
@heading Errors 

NF90_COPY_ATT returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The input or output variable ID is invalid for the specified netCDF
dataset.

@item
The specified attribute does not exist. 

@item
The output netCDF is not in define mode and the attribute is new for
the output dataset is larger than the existing attribute.

@item
The input or output netCDF ID does not refer to an open netCDF
dataset.
@end itemize

@heading Example 

Here is an example using NF90_COPY_ATT to copy the variable attribute
units from the variable rh in an existing netCDF dataset named foo.nc
to the variable avgrh in another existing netCDF dataset named bar.nc,
assuming that the variable avgrh already exists, but does not yet have
a units attribute:

@example
 use netcdf
 implicit none
 integer :: ncid1, ncid2, status
 integer :: RHVarID, avgRHVarID    ! Variable ID
 ... 
 status = nf90_open("foo.nc", nf90_nowrite, ncid1) 
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_open("bar.nc", nf90_write, ncid2) 
 if (status /= nf90_noerr) call handle_err(status)
 ... 
 ! Find the IDs of the variables
 status = nf90_inq_varid(ncid1, "rh", RHVarID)
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_inq_varid(ncid1, "avgrh", avgRHVarID)
 if (status /= nf90_noerr) call handle_err(status)
 ... 
 status = nf90_redef(ncid2)   ! Enter define mode
 if (status /= nf90_noerr) call handle_err(status)
 ! Copy variable attribute from "rh" in file 1 to "avgrh" in file 1
 status = nf90_copy_att(ncid1, RHVarID, "units", ncid2, avgRHVarID)
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_enddef(ncid2)
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_RENAME_ATT, NF90_DEL_ATT, NF90_COPY_ATT, Attributes
@section Rename an Attribute: NF90_RENAME_ATT
@findex NF90_RENAME_ATT
@cindex NF90_RENAME_ATT, example

The function NF90_RENAME_ATT changes the name of an attribute. If the
new name is longer than the original name, the netCDF dataset must be
in define mode. You cannot rename an attribute to have the same name
as another attribute of the same variable.

@heading Usage 
@example
 function nf90_rename_att(ncid, varid, curname, newname)
   integer,             intent( in) :: ncid,  varid
   character (len = *), intent( in) :: curname, newname
   integer                          :: nf90_rename_att
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item varid
ID of the attribute's variable, or NF90_GLOBAL for a global attribute
 
@item curname
The current attribute name.
 
@item newname
The new name to be assigned to the specified attribute. If the new
name is longer than the current name, the netCDF dataset must be in
define mode.
@end table
 
@heading Errors 

NF90_RENAME_ATT returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:
@itemize

@item
The specified variable ID is not valid. 

@item
The new attribute name is already in use for another attribute of the
specified variable.

@item
The specified netCDF dataset is in data mode and the new name is
longer than the old name.

@item
The specified attribute does not exist. 

@item
The specified netCDF ID does not refer to an open netCDF dataset.
@end itemize

@heading Example 

Here is an example using NF90_RENAME_ATT to rename the variable
attribute units to Units for a variable rh in an existing netCDF
dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid1, status
 integer :: RHVarID         ! Variable ID
 ... 
 status = nf90_open("foo.nc", nf90_nowrite, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ... 
 ! Find the IDs of the variables
 status = nf90_inq_varid(ncid, "rh", RHVarID)
 if (status /= nf90_noerr) call handle_err(status)
 ... 
 status = nf90_rename_att(ncid, RHVarID, "units", "Units")
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node NF90_DEL_ATT,  , NF90_RENAME_ATT, Attributes
@section NF90_DEL_ATT 
@findex NF90_DEL_ATT 
@cindex NF90_DEL_ATT , example

The function NF90_DEL_ATT deletes a netCDF attribute from an open netCDF
dataset. The netCDF dataset must be in define mode.

@heading Usage 
@example
 function nf90_del_att(ncid, varid, name)
   integer,             intent( in) :: ncid, varid
   character (len = *), intent( in) :: name
   integer                          :: nf90_del_att
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to NF90_OPEN, NF90_CREATE,
NF90_DEF_GRP, or associated inquiry functions such as NF90_INQ_NCID.
 
@item varid
ID of the attribute's variable, or NF90_GLOBAL for a global attribute.
 
@item name
The name of the attribute to be deleted.
@end table
 
@heading Errors 

NF90_DEL_ATT returns the value NF90_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The specified variable ID is not valid. 

@item
The specified netCDF dataset is in data mode. 

@item
The specified attribute does not exist. 

@item
The specified netCDF ID does not refer to an open netCDF dataset.
@end itemize

@heading Example 

Here is an example using NF90_DEL_ATT to delete the variable attribute
Units for a variable rh in an existing netCDF dataset named foo.nc:

@example
 use netcdf
 implicit none
 integer :: ncid1, status
 integer :: RHVarID         ! Variable ID
 ... 
 status = nf90_open("foo.nc", nf90_nowrite, ncid) 
 if (status /= nf90_noerr) call handle_err(status)
 ... 
 ! Find the IDs of the variables
 status = nf90_inq_varid(ncid, "rh", RHVarID)
 if (status /= nf90_noerr) call handle_err(status)
 ... 
 status = nf90_redef(ncid)   ! Enter define mode
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_del_att(ncid, RHVarID, "Units")
 if (status /= nf90_noerr) call handle_err(status)
 status = nf90_enddef(ncid)
 if (status /= nf90_noerr) call handle_err(status)
@end example

@node Summary of Fortran 90 Interface, Fortran 77 to Fortran 90 Transition Guide, Attributes, Top
@appendix Appendix A - Summary of Fortran 90 Interface

 Dataset Functions

@example
 function nf90_inq_libvers()
   character(len = 80) :: nf90_inq_libvers
 function nf90_strerror(ncerr)
   integer, intent( in) :: ncerr
   character(len = 80)  :: nf90_strerror
 function nf90_create(path, cmode, ncid)
   character (len = *), intent(in   ) :: path
   integer,             intent(in   ) :: cmode
   integer, optional,   intent(in   ) :: initialsize
   integer, optional,   intent(inout) :: chunksize
   integer,             intent(  out) :: ncid
   integer                            :: nf90_create
 function nf90_open(path, mode, ncid, chunksize)
   character (len = *), intent(in   ) :: path
   integer,             intent(in   ) :: mode
   integer,             intent(  out) :: ncid
   integer, optional,   intent(inout) :: chunksize
   integer                            :: nf90_open
 function nf90_set_fill(ncid, fillmode, old_mode)
   integer, intent( in) :: ncid, fillmode 
   integer, intent(out) :: old_mode
   integer              :: nf90_set_fill
 function nf90_redef(ncid)
   integer, intent( in) :: ncid
   integer              :: nf90_redef
 function nf90_enddef(ncid, h_minfree, v_align, v_minfree, r_align)
   integer,           intent( in) :: ncid
   integer, optional, intent( in) :: h_minfree, v_align, v_minfree, r_align
   integer                        :: nf90_enddef
 function nf90_sync(ncid)
   integer, intent( in) :: ncid
   integer              :: nf90_sync
 function nf90_abort(ncid)
   integer, intent( in) :: ncid
   integer              :: nf90_abort
 function nf90_close(ncid)
   integer, intent( in) :: ncid
   integer              :: nf90_close
 function nf90_Inquire(ncid, nDimensions, nVariables, nAttributes, &
                      unlimitedDimId)
   integer,           intent( in) :: ncid
   integer, optional, intent(out) :: nDimensions, nVariables, nAttributes, &  
                               unlimitedDimId
   integer                        :: nf90_Inquire
@end example

 Dimension functions

@example
 function nf90_def_dim(ncid, name, len, dimid)
   integer,             intent( in) :: ncid
   character (len = *), intent( in) :: name
   integer,             intent( in) :: len
   integer,             intent(out) :: dimid
   integer                          :: nf90_def_dim
 function nf90_inq_dimid(ncid, name, dimid)
   integer,             intent( in) :: ncid
   character (len = *), intent( in) :: name
   integer,             intent(out) :: dimid
   integer                          :: nf90_inq_dimid
 function nf90_inquire_dimension(ncid, dimid, name, len)
   integer,                       intent( in) :: ncid, dimid
   character (len = *), optional, intent(out) :: name
   integer,             optional, intent(out) :: len
   integer                                    :: nf90_inquire_dimension
 function nf90_rename_dim(ncid, dimid, name)
   integer,             intent( in) :: ncid
   character (len = *), intent( in) :: name
   integer,             intent( in) :: dimid
   integer                          :: nf90_rename_dim
@end example

 Variable functions

@example
 function nf90_def_var(ncid, name, xtype, dimids, varid)
   integer,               intent( in) :: ncid
   character (len = *),   intent( in) :: name
   integer,               intent( in) :: xtype
   integer, dimension(:), intent( in) :: dimids ! May be omitted, scalar, 
                                             ! vector
   integer                            :: nf90_def_var
 function nf90_inq_varid(ncid, name, varid)
   integer,             intent( in) :: ncid
   character (len = *), intent( in) :: name
   integer,             intent(out) :: varid
   integer                          :: nf90_inq_varid
 function nf90_inquire_variable(ncid, varid, name, xtype, ndims, &
                                dimids, nAtts)
   integer,                         intent( in) :: ncid, varid
   character (len = *),   optional, intent(out) :: name
   integer,               optional, intent(out) :: xtype, ndims 
   integer, dimension(*), optional, intent(out) :: dimids
   integer,               optional, intent(out) :: nAtts
   integer                                      :: nf90_inquire_variable
 function nf90_put_var(ncid, varid, values, start, stride, map)
   integer,                         intent( in) :: ncid, varid
   any valid type, scalar or array of any rank, &
                                    intent( in) :: values
   integer, dimension(:), optional, intent( in) :: start, count, stride, map
   integer                                      :: nf90_put_var
 function nf90_get_var(ncid, varid, values, start, stride, map)
   integer,                         intent( in) :: ncid, varid
   any valid type, scalar or array of any rank, &
                                    intent(out) :: values
   integer, dimension(:), optional, intent( in) :: start, count, stride, map
   integer                                      :: nf90_get_var
 function nf90_rename_var(ncid, varid, newname)
   integer,             intent( in) :: ncid, varid
   character (len = *), intent( in) :: newname
   integer                          :: nf90_rename_var
@end example

 Attribute functions

@example
 function nf90_inquire_attribute(ncid, varid, name, xtype, len, attnum)
   integer,             intent( in)           :: ncid, varid
   character (len = *), intent( in)           :: name
   integer,             intent(out), optional :: xtype, len, attnum
   integer                                    :: nf90_inquire_attribute
 function nf90_inq_attname(ncid, varid, attnum, name)
   integer,             intent( in) :: ncid, varid, attnum
   character (len = *), intent(out) :: name
   integer                          :: nf90_inq_attname
 function nf90_put_att(ncid, varid, name, values)
   integer,            intent( in) :: ncid, varid
   character(len = *), intent( in) :: name
   any valid type, scalar or array of rank 1, &
                       intent( in) :: values
   integer                         :: nf90_put_att
 function nf90_get_att(ncid, varid, name, values)
   integer,            intent( in) :: ncid, varid
   character(len = *), intent( in) :: name
   any valid type, scalar or array of rank 1, &
                       intent(out) :: values
   integer                          :: nf90_get_att
 function nf90_copy_att(ncid_in, varid_in, name, ncid_out, varid_out)
   integer,             intent( in) :: ncid_in,  varid_in
   character (len = *), intent( in) :: name
   integer,             intent( in) :: ncid_out, varid_out
   integer                          :: nf90_copy_att
 function nf90_rename_att(ncid, varid, curname, newname)
   integer,             intent( in) :: ncid,  varid
   character (len = *), intent( in) :: curname, newname
   integer                          :: nf90_rename_att
 function nf90_del_att(ncid, varid, name)
   integer,             intent( in) :: ncid, varid
   character (len = *), intent( in) :: name
   integer                          :: nf90_del_att
@end example

@node Fortran 77 to Fortran 90 Transition Guide, Combined Index, Summary of Fortran 90 Interface, Top
@appendix Appendix B - Fortran 77 to Fortran 90 Transition Guide

@unnumberedsubsec The new Fortran 90 interface 

The Fortran 90 interface to the netCDF library closely follows the
Fortran 77 interface. In most cases, function and constant names and
argument lists are the same, except that nf90_ replaces nf_ in
names. The Fortran 90 interface is much smaller than the Fortran 77
interface, however. This has been accomplished by using optional
arguments and overloaded functions wherever possible.

Because Fortran 77 is a subset of Fortran 90, there is no reason to
modify working Fortran code to use the Fortran 90 interface. New code,
however, can easily be patterned after existing Fortran while taking
advantage of the simpler interface. Some compilers may provide
additional support when using Fortran 90. For example, compilers may
issue warnings if arguments with intent( in) are not set before they
are passed to a procedure.

The Fortran 90 interface is currently implemented as a set of wrappers
around the base Fortran subroutines in the netCDF distribution. Future
versions may be implemented entirely in Fortran 90, adding additional
error checking possibilities.

@unnumberedsubsec Changes to Inquiry functions 

In the Fortran 90 interface there are two inquiry functions each for
dimensions, variables, and attributes, and a single inquiry function
for datasets. These functions take optional arguments, allowing users
to request only the information they need. These functions replace the
many-argument and single-argument inquiry functions in the Fortran
interface.

As an example, compare the attribute inquiry functions in the Fortran
90 interface

@example
 function nf90_inquire_attribute(ncid, varid, name, xtype, len, attnum)
   integer,             intent( in)           :: ncid, varid
   character (len = *), intent( in)           :: name
   integer,             intent(out), optional :: xtype, len, attnum
   integer                                    :: nf90_inquire_attribute
 function nf90_inq_attname(ncid, varid, attnum, name)
   integer,             intent( in) :: ncid, varid, attnum
   character (len = *), intent(out) :: name
   integer                          :: nf90_inq_attname
@end example

with those in the Fortran interface 

@example
 INTEGER FUNCTION  NF_INQ_ATT        (NCID, VARID, NAME, xtype, len)
 INTEGER FUNCTION  NF_INQ_ATTID      (NCID, VARID, NAME, attnum)
 INTEGER FUNCTION  NF_INQ_ATTTYPE    (NCID, VARID, NAME, xtype)
 INTEGER FUNCTION  NF_INQ_ATTLEN     (NCID, VARID, NAME, len)
 INTEGER FUNCTION  NF_INQ_ATTNAME    (NCID, VARID, ATTNUM, name)
@end example

@unnumberedsubsec Changes to put and get function 

The biggest simplification in the Fortran 90 is in the nf90_put_var
and nf90_get_var functions. Both functions are overloaded: the values
argument can be a scalar or an array any rank (7 is the maximum rank
allowed by Fortran 90), and may be of any numeric type or the default
character type. The netCDF library provides transparent conversion
between the external representation of the data and the desired
internal representation.

The start, count, stride, and map arguments to nf90_put_var and
nf90_get_var are optional. By default, data is read from or written to
consecutive values of starting at the origin of the netCDF variable;
the shape of the argument determines how many values are read from or
written to each dimension. Any or all of these arguments may be
supplied to override the default behavior.

Note also that Fortran 90 allows arbitrary array sections to be passed
to any procedure, which may greatly simplify programming. For examples
see @ref{NF90_PUT_VAR} and @ref{NF90_GET_VAR}.

@node Combined Index,  , Fortran 77 to Fortran 90 Transition Guide, Top
@unnumbered Index

@printindex cp

@bye
End:
