NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)NAMEnetcdf - Unidata Network Common Data Form (netCDF)
library, version 3 interface
SYNOPSIS
#include "netcdf.h"
cc ... -lnetcdf
LIBRARY VERSION
This document describes version 3 of Unidata netCDF data-
access interface for the C programming language.
const char* nc_inq_libvers()
Returns a string identifying the version of the
netCDF library, and when it was built, like: "3.1a
of Aug 22 1996 12:57:47 $".
The RCS ident(1) command will find a string like "$Id:
@(#) netcdf library version 3.1a of Sep 6 1996 15:56:26
$" in the library. The SCCS what(1) command will find a
string like "netcdf library version 3.1a of Aug 23 1996
16:07:40 $".
RETURN VALUES
All netCDF functions (except nc_inq_libvers() and
nc_strerror()) return an integer status. This behavior
replaces the ncerr() function used in previous versions of
the library. If this returned status value is not equal
to NC_NOERR (zero), it indicates that an error occurred.
The possible status values are defined in system include
file <errno.h> and in "netcdf.h".
const char* nc_strerror(int status)
Returns a string textual translation of the status
value, like "Attribute or variable name contains
illegal characters" or "No such file or directory".
int nc_create(const char path[], int cmode, int* ncid)
(Corresponds to nccreate() in version 2)
Creates a new netCDF dataset at path, returning a
netCDF ID in ncid. The argument cmode may include
the bitwise-or of the following flags: NC_NOCLOBBER
to protect existing datasets (default silently
blows them away), NC_SHARE for synchronous dataset
updates (default is to buffer accesses), and
NC_LOCK (not yet implemented). When a netCDF
dataset is created, is is opened NC_WRITE. The new
Printed: 101.10.25 18 April 1997 1
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
netCDF dataset is in define mode.
int nc__create(const char path[], int cmode, size_t ini_
tialsize, size_t* chunksize, int* ncid)
Like nc_create() but has additional performance
tuning parameters.
The argument initialsize sets the initial size of
the file at creation time.
See nc__open() below for an explanation of the
chunksize parameter.
int nc_open(const char path[], int mode, int* ncid)
(Corresponds to ncopen() in version 2)
Opens a existing netCDF dataset at path returning a
netCDF ID in ncid. The type of access is described
by the mode parameter, which may include the bit
wise-or of the following flags: NC_WRITE for read-
write access (default read-only), NC_SHARE for syn
chronous dataset updates (default is to buffer ac
cesses), and NC_LOCK (not yet implemented).
int nc__open(const char path[], int mode, size_t* chunk_
size, int* ncid)
Like nc_open() but has an additional performance
tuning parameter.
The argument referenced by chunksize controls a
space versus time tradeoff, memory allocated in the
netcdf library versus number of system calls. Be
cause of internal requirements, the value may not
be set to exactly the value requested. The actual
value chosen is returned by reference. Using the
value NC_SIZEHINT_DEFAULT causes the library to
choose a default. How the system choses the de
fault depends on the system. On many systems, the
"preferred I/O block size" is available from the
stat() system call, struct stat member st_blksize.
If this is available it is used. Lacking that,
twice the system pagesize is used. Lacking a call
to discover the system pagesize, we just set de
fault chunksize to 8192.
The chunksize is a property of a given open netcdf
descriptor ncid, it is not a persistent property of
the netcdf dataset.
int nc_redef(int ncid)
Printed: 101.10.25 18 April 1997 2
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
(Corresponds to ncredef() in version 2)
Puts an open netCDF dataset into define mode, so
dimensions, variables, and attributes can be added
or renamed and attributes can be deleted.
int nc_enddef(int ncid)
(Corresponds to ncendef() in version 2)
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. Some data values may be
written as well, see "VARIABLE PREFILLING" below.
After a successful call, variable data can be read
or written to the dataset.
int nc__enddef(int ncid, size_t h_minfree, size_t v_align,
size_t v_minfree, size_t r_align)
Like nc_enddef() but has additional performance
tuning parameters.
Caution: this function exposes internals of the
netcdf version 1 file format. It may not be avail
able on 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 vari
ables). 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. Typ
ically, there is no space between the sections.
This causes copying overhead to accrue if one wish
es to change the size of the sections, as may hap
pen when changing names of things, text attribute
values, adding attributes or adding variables. Al
so, 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 nc_redef(), nc_enddef() by re
questing that minfree bytes be available at the end
of the section. The h_minfree parameter sets the
pad at the end of the "header" section. The v_min_
free parameter sets the pad at the end of the data
section for fixed size variables.
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
Printed: 101.10.25 18 April 1997 3
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
which is a multiple of the align parameter. The
flag value NC_ALIGN_CHUNK tells the library to use
the chunksize (see above) as the align parameter.
The v_align parameter controls the alignment of the
beginning of the data section for fixed size vari
ables. The r_align parameter controls the align
ment of the beginning of the data section for vari
ables which have an unlimited dimension (record
variables).
The file format requires mod 4 alignment, so the
align parameters are silently rounded up to multi
ples of 4. The usual call, nc_enddef(ncid) is
equivalent to nc__enddef(ncid, 0, 4, 0, 4).
The file format does not contain a "record size"
value, this is calculated from the sizes of the
record variables. This unfortunate fact prevents us
from providing minfree and alignment control of the
"records" in a netcdf file. If you add a variable
which has an unlimited dimension, the third section
will always be copied with the new variable added.
int nc_sync(int ncid)
(Corresponds to ncsync() in version 2)
Unless the NC_SHARE bit is set in nc_open() or
nc_create(), accesses to the underlying netCDF
dataset are buffered by the library. This function
synchronizes the state of the underlying dataset
and the library. This is done automatically by
nc_close() and nc_enddef().
int nc_abort(int ncid)
(Corresponds to ncabort() in version 2)
You don't need to call this function. This func
tion is called automatically by nc_close() if the
netCDF was in define mode and something goes wrong
with the commit. If the netCDF dataset isn't in
define mode, then this function is equivalent to
nc_close(). If it is called after nc_redef(), but
before nc_enddef(), the new definitions are not
committed and the dataset is closed. If it is
called after nc_create() but before nc_enddef(),
the dataset disappears.
int nc_close(int ncid)
(Corresponds to ncclose() in version 2)
Closes an open netCDF dataset. If the dataset is
Printed: 101.10.25 18 April 1997 4
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
in define mode, nc_enddef() will be called before
closing. After a dataset is closed, its ID may be
reassigned to another dataset.
int nc_inq(int ncid, int* ndims, int* nvars, int* natts,
int* unlimdimid)
int nc_inq_ndims(int ncid, int* ndims)
int nc_inq_nvars(int ncid, int* nvars)
int nc_inq_natts(int ncid, int* natts)
int nc_inq_unlimdim(int ncid, int* unlimdimid)
(Replace ncinquire() in version 2)
Use these functions to find out what is in a netCDF
dataset. Upon successful return, ndims will con
tain the number of dimensions defined for this
netCDF dataset, nvars will contain the number of
variables, natts will contain the number of at
tributes, and unlimdimid will contain the dimension
ID of the unlimited dimension if one exists, or -1
otherwise. If any of the return parameters is a
NULL pointer, then the corresponding information
will not be returned; hence, no space need be allo
cated for it.
int nc_def_dim(int ncid, const char name[], size_t len,
int* dimid)
(Corresponds to ncdimdef() in version 2)
Adds a new dimension to an open netCDF dataset,
which must be in define mode. name is the dimen
sion name. If dimid is not a NULL pointer then up
on successful completion dimid will contain the di
mension ID of the newly created dimension.
int nc_inq_dimid(int ncid, const char name[], int* dimid)
(Corresponds to ncdimid() in version 2)
Given a dimension name, returns the ID of a netCDF
dimension in dimid.
int nc_inq_dim(int ncid, int dimid, char name[], size_t*
len)
int nc_inq_dimname(int ncid, int dimid, char name[])
int nc_inq_dimlen(int ncid, int dimid, size_t* len)
Printed: 101.10.25 18 April 1997 5
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
(Replace ncdiminq() in version 2)
Use these functions to find out about a dimension.
If either the name argument or len argument is a
NULL pointer, then the associated information will
not be returned. Otherwise, name should be big
enough (NC_MAX_NAME) to hold the dimension name as
the name will be copied into your storage. The
length return parameter, len will contain the size
of the dimension. For the unlimited dimension, the
returned length is the current maximum value used
for writing into any of the variables which use the
dimension.
int nc_rename_dim(int ncid, int dimid, const char name[])
(Corresponds to ncdimrename() in version 2)
Renames an existing dimension 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 dimension to have the same name
as another dimension.
int nc_def_var(int ncid, const char name[], nc_type xtype,
int ndims, const int dimids[], int* varid)
(Corresponds to ncvardef() in version 2)
Adds a new variable to a netCDF dataset. The netCDF
must be in define mode. If not NULL, then varid
will be set to the netCDF variable ID.
int nc_inq_varid(int ncid, const char name[], int* varid)
(Corresponds to ncvarid() in version 2)
Returns the ID of a netCDF variable in varid given
its name.
int nc_inq_var(int ncid, int varid, char name[], nc_type*
xtype, int* ndims, int dimids[], int* natts)
int nc_inq_varname(int ncid, int varid, char name[])
int nc_inq_vartype(int ncid, int varid, nc_type* xtype)
int nc_inq_varndims(int ncid, int varid, int* ndims)
int nc_inq_vardimid(int ncid, int varid, int dimids[])
int nc_inq_varnatts(int ncid, int varid, int* natts)
(Replace ncvarinq() in version 2)
Printed: 101.10.25 18 April 1997 6
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
Returns information about a netCDF variable, given
its ID. If any of the return parameters (name,
xtype, ndims, dimids, or natts) is a NULL pointer,
then the corresponding information will not be re
turned; hence, no space need be allocated for it.
int nc_rename_var(int ncid, int varid, const char name[])
(Corresponds to ncvarrename() in version 2)
Changes the name of a netCDF variable. If the new
name is longer than the old name, the netCDF must
be in define mode. You cannot rename a variable to
have the name of any existing variable.
int nc_put_var_text(int ncid, int varid, const char out[])
int nc_put_var_uchar(int ncid, int varid, const unsigned
char out[])
int nc_put_var_schar(int ncid, int varid, const signed
char out[])
int nc_put_var_short(int ncid, int varid, const short
out[])
int nc_put_var_int(int ncid, int varid, const int out[])
int nc_put_var_long(int ncid, int varid, const long out[])
int nc_put_var_float(int ncid, int varid, const float
out[])
int nc_put_var_double(int ncid, int varid, const double
out[])
(Replace ncvarput() in version 2)
Writes an entire netCDF variable (i.e. all the val
ues). The netCDF dataset must be open and in data
mode. The type of the data is specified in the
function name, and it is converted to the external
type of the specified variable, if possible, other
wise an NC_ERANGE error is returned.
int nc_get_var_text(int ncid, int varid, char in[])
int nc_get_var_uchar(int ncid, int varid, unsigned char
in[])
int nc_get_var_schar(int ncid, int varid, signed char
in[])
int nc_get_var_short(int ncid, int varid, short in[])
Printed: 101.10.25 18 April 1997 7
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
int nc_get_var_int(int ncid, int varid, int in[])
int nc_get_var_long(int ncid, int varid, long in[])
int nc_get_var_float(int ncid, int varid, float in[])
int nc_get_var_double(int ncid, int varid, double in[])
(Replace ncvarget() in version 2)
Reads an entire netCDF variable (i.e. all the val
ues). The netCDF dataset must be open and in data
mode. The data is converted from the external type
of the specified variable, if necessary, to the
type specified in the function name. If conversion
is not possible, an NC_ERANGE error is returned.
int nc_put_var1_text(int ncid, int varid, const size_t in_
dex[], char *out)
int nc_put_var1_uchar(int ncid, int varid, const size_t
index[], unsigned char *out)
int nc_put_var1_schar(int ncid, int varid, const size_t
index[], signed char *out)
int nc_put_var1_short(int ncid, int varid, const size_t
index[], short *out)
int nc_put_var1_int(int ncid, int varid, const size_t in_
dex[], int *out)
int nc_put_var1_long(int ncid, int varid, const size_t in_
dex[], long *out)
int nc_put_var1_float(int ncid, int varid, const size_t
index[], float *out)
int nc_put_var1_double(int ncid, int varid, const size_t
index[], double *out)
(Replace ncvarput1() in version 2)
Puts a single data value into a variable at the po
sition index of an open netCDF dataset that is in
data mode. The type of the data is specified in
the function name, and it is converted to the ex
ternal type of the specified variable, if possible,
otherwise an NC_ERANGE error is returned.
int nc_get_var1_text(int ncid, int varid, const size_t in_
dex[], char* in)
int nc_get_var1_uchar(int ncid, int varid, const size_t
Printed: 101.10.25 18 April 1997 8
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
index[], unsigned char* in)
int nc_get_var1_schar(int ncid, int varid, const size_t
index[], signed char* in)
int nc_get_var1_short(int ncid, int varid, const size_t
index[], short* in)
int nc_get_var1_int(int ncid, int varid, const size_t in_
dex[], int* in)
int nc_get_var1_long(int ncid, int varid, const size_t in_
dex[], long* in)
int nc_get_var1_float(int ncid, int varid, const size_t
index[], float* in)
int nc_get_var1_double(int ncid, int varid, const size_t
index[], double* in)
(Replace ncvarget1() in version 2)
Gets a single data value from a variable at the po
sition index of an open netCDF dataset that is in
data mode. The data is converted from the external
type of the specified variable, if necessary, to
the type specified in the function name. If con
version is not possible, an NC_ERANGE error is re
turned.
int nc_put_vara_text(int ncid, int varid, const size_t
start[], const size_t count[], const char out[])
int nc_put_vara_uchar(int ncid, int varid, const size_t
start[], const size_t count[], const unsigned char
out[])
int nc_put_vara_schar(int ncid, int varid, const size_t
start[], const size_t count[], const signed char
out[])
int nc_put_vara_short(int ncid, int varid, const size_t
start[], const size_t count[], const short out[])
int nc_put_vara_int(int ncid, int varid, const size_t
start[], const size_t count[], const int out[])
int nc_put_vara_long(int ncid, int varid, const size_t
start[], const size_t count[], const long out[])
int nc_put_vara_float(int ncid, int varid, const size_t
start[], const size_t count[], const float out[])
int nc_put_vara_double(int ncid, int varid, const size_t
Printed: 101.10.25 18 April 1997 9
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
start[], const size_t count[], const double out[])
(Replace ncvarput() in version 2)
Writes an array section of values into a netCDF
variable of an open netCDF dataset, which must be
in data mode. The array section is specified by
the start and count vectors, which give the start
ing index and count of values along each dimension
of the specified variable. The type of the data is
specified in the function name and is converted to
the external type of the specified variable, if
possible, otherwise an NC_ERANGE error is returned.
int nc_get_vara_text(int ncid, int varid, const size_t
start[], const size_t count[], char in[])
int nc_get_vara_uchar(int ncid, int varid, const size_t
start[], const size_t count[], unsigned char in[])
int nc_get_vara_schar(int ncid, int varid, const size_t
start[], const size_t count[], signed char in[])
int nc_get_vara_short(int ncid, int varid, const size_t
start[], const size_t count[], short in[])
int nc_get_vara_int(int ncid, int varid, const size_t
start[], const size_t count[], int in[])
int nc_get_vara_long(int ncid, int varid, const size_t
start[], const size_t count[], long in[])
int nc_get_vara_float(int ncid, int varid, const size_t
start[], const size_t count[], float in[])
int nc_get_vara_double(int ncid, int varid, const size_t
start[], const size_t count[], double in[])
(Corresponds to ncvarget() in version 2)
Reads an array section of values from a netCDF
variable of an open netCDF dataset, which must be
in data mode. The array section is specified by
the start and count vectors, which give the start
ing index and count of values along each dimension
of the specified variable. The data is converted
from the external type of the specified variable,
if necessary, to the type specified in the function
name. If conversion is not possible, an NC_ERANGE
error is returned.
int nc_put_vars_text(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], const char out[])
Printed: 101.10.25 18 April 1997 10
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
int nc_put_vars_uchar(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], const unsigned char out[])
int nc_put_vars_schar(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], const signed char out[])
int nc_put_vars_short(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], const short out[])
int nc_put_vars_int(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], const int out[])
int nc_put_vars_long(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], const long out[])
int nc_put_vars_float(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], const float out[])
int nc_put_vars_double(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], const double out[])
(Corresponds to ncvarputg() in version 2)
These functions are used for strided output, which
is like the array section output described above,
except that the sampling stride (the interval be
tween accessed values) is specified for each dimen
sion. For an explanation of the sampling stride
vector, see COMMON ARGUMENTS DESCRIPTIONS below.
int nc_get_vars_text(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], char in[])
int nc_get_vars_uchar(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], unsigned char in[])
int nc_get_vars_schar(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], signed char in[])
int nc_get_vars_short(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], short in[])
int nc_get_vars_int(int ncid, int varid, const size_t
Printed: 101.10.25 18 April 1997 11
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
start[], const size_t count[], const size_t
stride[], int in[])
int nc_get_vars_long(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], long in[])
int nc_get_vars_float(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], float in[])
int nc_get_vars_double(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], double in[])
(Corresponds to ncvargetg() in version 2)
These functions are used for strided input, which
is like the array section input described above,
except that the sampling stride (the interval be
tween accessed values) is specified for each dimen
sion. For an explanation of the sampling stride
vector, see COMMON ARGUMENTS DESCRIPTIONS below.
int nc_put_varm_text(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, const char out[])
int nc_put_varm_uchar(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, const unsigned char out[])
int nc_put_varm_schar(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, const signed char out[])
int nc_put_varm_short(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, const short out[])
int nc_put_varm_int(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, const int out[])
int nc_put_varm_long(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, const long out[])
int nc_put_varm_float(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, const float out[])
int nc_put_varm_double(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
Printed: 101.10.25 18 April 1997 12
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
stride[], imap, const double out[])
(Corresponds to ncvarputg() in version 2)
These functions are used for mapped output, which
is like strided output described above, except that
an additional index mapping vector is provided to
specify the in-memory arrangement of the data val
ues. For an explanation of the index mapping vec
tor, see COMMON ARGUMENTS DESCRIPTIONS below.
int nc_get_varm_text(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, char in[])
int nc_get_varm_uchar(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, unsigned char in[])
int nc_get_varm_schar(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, signed char in[])
int nc_get_varm_short(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, short in[])
int nc_get_varm_int(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, int in[])
int nc_get_varm_long(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, long in[])
int nc_get_varm_float(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, float in[])
int nc_get_varm_double(int ncid, int varid, const size_t
start[], const size_t count[], const size_t
stride[], imap, double in[])
(Corresponds to ncvargetg() in version 2)
These functions are used for mapped input, which is
like strided input described above, except that an
additional index mapping vector is provided to
specify the in-memory arrangement of the data val
ues. For an explanation of the index mapping vec
tor, see COMMON ARGUMENTS DESCRIPTIONS below.
int nc_put_att_text(int ncid, int varid, const char
name[], nc_type xtype, size_t len, const char
Printed: 101.10.25 18 April 1997 13
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
out[])
int nc_put_att_uchar(int ncid, int varid, const char
name[], nc_type xtype, size_t len, const unsigned
char out[])
int nc_put_att_schar(int ncid, int varid, const char
name[], nc_type xtype, size_t len, const signed
char out[])
int nc_put_att_short(int ncid, int varid, const char
name[], nc_type xtype, size_t len, const short
out[])
int nc_put_att_int(int ncid, int varid, const char name[],
nc_type xtype, size_t len, const int out[])
int nc_put_att_long(int ncid, int varid, const char
name[], nc_type xtype, size_t len, const long
out[])
int nc_put_att_float(int ncid, int varid, const char
name[], nc_type xtype, size_t len, const float
out[])
int nc_put_att_double(int ncid, int varid, const char
name[], nc_type xtype, size_t len, const double
out[])
(Replace ncattput() in version 2)
Unlike variables, attributes do not have separate
functions for defining and writing values. This
family of functions defines a new attribute with a
value or changes the value of an existing at
tribute. If the attribute is new, or if the space
required to store the attribute value is greater
than before, the netCDF dataset must be in define
mode. The parameter len is the number of values
from out to transfer. It is often one, except that
for nc_put_att_text() it will usually be
strlen(out).
For these functions, the type component of the
function name refers to the in-memory type of the
value, whereas the xtype argument refers to the ex
ternal type for storing the value. An NC_ERANGE
error results if a conversion between these types
is not possible. In this case the value is repre
sented with the appropriate fill-value for the as
sociated external type.
int nc_inq_attname(int ncid, int varid, int attnum, char
name[])
Printed: 101.10.25 18 April 1997 14
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
(Corresponds to ncattname() in version 2)
Gets the name of an attribute, given its variable
ID and attribute 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 num
ber of an attribute is more volatile than the name,
since it can change when other attributes of the
same variable are deleted. The attributes for each
variable are numbered from 0 (the first attribute)
to nvatts-1, where nvatts is the number of at
tributes for the variable, as returned from a call
to nc_inq_varnatts(). If the name parameter is a
NULL pointer, no name will be returned and no space
need be allocated.
int nc_inq_att(int ncid, int varid, const char name[],
nc_type* xtype, size_t* len)
int nc_inq_attid(int ncid, int varid, const char name[],
int* attnum)
int nc_inq_atttype(int ncid, int varid, const char name[],
nc_type* xtype)
int nc_inq_attlen(int ncid, int varid, const char name[],
size_t* len)
(Corresponds to ncattinq() in version 2)
These functions return information about a netCDF
attribute, given its variable ID and name. The in
formation returned is the external type in xtype
and the number of elements in the attribute as len.
If any of the return arguments is a NULL pointer,
the specified information will not be returned.
int nc_copy_att(int ncid, int varid_in, const char name[],
int ncid_out, int varid_out)
(Corresponds to ncattcopy() in version 2)
Copies an attribute from one netCDF dataset to an
other. It can also be used to copy an attribute
from one variable to another within the same
netCDF. ncid_in is the netCDF ID of an input
netCDF dataset from which the attribute will be
copied. varid_in is the ID of the variable in the
input netCDF dataset from which the attribute will
be copied, or NC_GLOBAL for a global attribute.
name is the name of the attribute in the input
netCDF dataset to be copied. ncid_out is the
Printed: 101.10.25 18 April 1997 15
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
netCDF ID of the output netCDF dataset to which the
attribute will be copied. It is permissible for
the input and output netCDF ID's to be the same.
The output netCDF dataset should be in define mode
if the attribute to be copied does not already ex
ist for the target variable, or if it would cause
an existing target attribute to grow. varid_out is
the ID of the variable in the output netCDF dataset
to which the attribute will be copied, or NC_GLOBAL
to copy to a global attribute.
int nc_rename_att(int ncid, int varid, const char name[],
const char newname[])
(Corresponds to ncattrename()
Changes the name of an attribute. If the new name
is longer than the original name, the netCDF must
be in define mode. You cannot rename an attribute
to have the same name as another attribute of the
same variable. name is the original attribute
name. newname is the new name to be assigned to
the specified attribute. If the new name is longer
than the old name, the netCDF dataset must be in
define mode.
int nc_del_att(int ncid, int varid, const char name[])
(Corresponds to ncattdel() in version 2)
Deletes an attribute from a netCDF dataset. The
dataset must be in define mode.
int nc_get_att_text(int ncid, int varid, const char
name[], char in[])
int nc_get_att_uchar(int ncid, int varid, const char
name[], unsigned char in[])
int nc_get_att_schar(int ncid, int varid, const char
name[], signed char in[])
int nc_get_att_short(int ncid, int varid, const char
name[], short in[])
int nc_get_att_int(int ncid, int varid, const char name[],
int in[])
int nc_get_att_long(int ncid, int varid, const char
name[], long in[])
int nc_get_att_float(int ncid, int varid, const char
name[], float in[])
Printed: 101.10.25 18 April 1997 16
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
int nc_get_att_double(int ncid, int varid, const char
name[], double in[])
(Replace ncattget() in version 2)
Gets the value(s) of a netCDF attribute, given its
variable ID and name. Converts from the external
type to the type specified in the function name, if
possible, otherwise returns an NC_ERANGE error.
All elements of the vector of attribute values are
returned, so you must allocate enough space to hold
them. If you don't know how much space to reserve,
call nc_inq_attlen() first to find out the length
of the attribute.
COMMON ARGUMENT DESCRIPTIONS
In this section we define some common arguments which are
used in the "FUNCTION DESCRIPTIONS" section.
int ncid
is the netCDF ID returned from a previous, success
ful call to nc_open() or nc_create()
char name[]
is the name of a dimension, variable, or attribute.
It shall begin with an alphabetic character, fol
lowed by zero or more alphanumeric characters in
cluding the underscore (`_') or hyphen (`-'). Case
is significant. As an input argument, it shall be
a pointer to a 0-terminated string; as an output
argument, it shall be the address of a buffer in
which to hold such a string. The maximum allowable
number of characters (excluding the terminating 0)
is NC_MAX_NAME. Names that begin with an under
score (`_') are reserved for use by the netCDF in
terface.
nc_type xtype
specifies the external data type of a netCDF vari
able or attribute and is one of the following:
NC_BYTE, NC_CHAR, NC_SHORT, NC_INT, NC_FLOAT, or
NC_DOUBLE. These are used to specify 8-bit inte
gers, characters, 16-bit integers, 32-bit integers,
32-bit IEEE floating point numbers, and 64-bit IEEE
floating-point numbers, respectively. (NC_INT cor
responds to NC_LONG in version 2, to specify a
32-bit integer).
int dimids[]
is a vector of dimension ID's and defines the shape
of a netCDF variable. The size of the vector shall
be greater than or equal to the rank (i.e. the num
ber of dimensions) of the variable (ndims). The
vector shall be ordered by the speed with which a
Printed: 101.10.25 18 April 1997 17
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
dimension varies: dimids[ndims-1] shall be the di
mension ID of the most rapidly varying dimension
and dimids[0] shall be the dimension ID of the most
slowly varying dimension. The maximum possible
number of dimensions for a variable is given by the
symbolic constant NC_MAX_VAR_DIMS.
int dimid
is the ID of a netCDF dimension. netCDF dimension
ID's are allocated sequentially from the non-nega
tive integers beginning with 0.
int ndims
is either the total number of dimensions in a
netCDF dataset or the rank (i.e. the number of di
mensions) of a netCDF variable. The value shall
not be negative or greater than the symbolic con
stant NC_MAX_VAR_DIMS.
int varid
is the ID of a netCDF variable or (for the at
tribute-access functions) the symbolic constant
NC_GLOBAL, which is used to reference global at
tributes. netCDF variable ID's are allocated se
quentially from the non-negative integers beginning
with 0.
int* natts
is the number of global attributes in a netCDF
dataset for the nc_inquire() function or the num
ber of attributes associated with a netCDF variable
for the nc_varinq() function.
const size_t index[]
specifies the indicial coordinates of the netCDF
data value to be accessed. The indices start at 0;
thus, for example, the first data value of a two-
dimensional variable is (0,0). The size of the
vector shall be at least the rank of the associated
netCDF variable and its elements shall correspond,
in order, to the variable's dimensions.
const size_t start[]
specifies the starting point for accessing a netCDF
variable's data values in terms of the indicial co
ordinates of the corner of the array section. The
indices start at 0; thus, the first data value of a
variable is (0, 0, ..., 0). The size of the vector
shall be at least the rank of the associated netCDF
variable and its elements shall correspond, in or
der, to the variable's dimensions.
const size_t count[]
specifies the number of indices selected along each
Printed: 101.10.25 18 April 1997 18
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
dimension of the array section. Thus, to access a
single value, for example, specify count as (1, 1,
..., 1). Note that, for strided I/O, this argument
must be adjusted to be compatible with the stride
and start arguments so that the interaction of the
three does not attempt to access an invalid data
co-ordinate. The elements of the count vector cor
respond, in order, to the variable's dimensions.
const size_t stride[]
specifies the sampling interval along each dimen
sion of the netCDF variable. The elements of the
stride vector correspond, in order, to the netCDF
variable's dimensions (stride[0]) gives the sam
pling interval along the most slowly varying dimen
sion 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.). A
NULL stride argument is treated as (1, 1, ... , 1).
imap 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 (imap[0] gives the distance
between elements of the internal array correspond
ing to the most slowly varying dimension of the
netCDF variable). Distances between elements are
specified in type-independent units of elements
(the distance between internal elements that occupy
adjacent memory locations is 1 and not the ele
ment's byte-length as in netCDF 2). A NULL pointer
means the memory-resident values have the same
structure as the associated netCDF variable.
VARIABLE PREFILLING
By default, the netCDF interface sets the values of all
newly-defined variables of finite length (i.e. those that
do not have an unlimited, dimension) to the type-dependent
fill-value associated with each variable. This is done
when nc_enddef() is called. The fill-value for a variable
may be changed from the default value by defining the at
tribute `_FillValue' for the variable. This attribute
must have the same type as the variable and be of length
one.
Variables with an unlimited dimension are also prefilled,
but on an `as needed' basis. For example, if the first
write of such a variable is to position 5, then positions
0 through 4 (and no others) would be set to the fill-value
at the same time.
Printed: 101.10.25 18 April 1997 19
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
This default prefilling of data values may be disabled by
or'ing the NC_NOFILL flag into the mode parameter of
nc_open() or nc_create(), or, by calling the function
nc_set_fill() with the argument NC_NOFILL. For variables
that do not use the unlimited dimension, this call must be
made before nc_enddef(). For variables that use the un
limited dimension, this call may be made at any time.
One can obtain increased performance of the netCDF inter
face by using this feature, but only at the expense of re
quiring the application to set every single data value.
The performance enhancing behavior of this function is de
pendent on the particulars of the implementation and
dataset format. The flag value controlled by
nc_set_fill() is per netCDF ID, not per variable or per
write. Allowing this to change affects the degree to
which a program can be effectively parallelized. Given
all of this, we state that the use of this feature may not
be available (or even needed) in future releases. Program
mers are cautioned against heavy reliance upon this fea
ture.
int nc_setfill(int ncid, int fillmode, int* old_fillemode)
(Corresponds to ncsetfill() in version 2)
Determines whether or not variable prefilling will
be done (see above). The netCDF dataset shall be
writable. fillmode is either NC_FILL to enable
prefilling (the default) or NC_NOFILL to disable
prefilling. This function returns the previous
setting in old_fillmode.
MPP FUNCTION DESCRIPTIONS
Additional functions for use on Cray MPP machines
(_CRAYMPP). These are used to set and inquire which PE is
the base for MPP for a particular netCDF. These are only
relevant when using the Cray ``global'' Flexible File I/O
layer and desire to have only a subset of PEs to open the
specific netCDF file. For technical reasons, these func
tions are available on all platforms. On a platform other
than Cray MPP, it is as if only processor available were
processor 0.
To use this feature, you need to specify a communicator
group and call glio_group_mpi() or glio_group_shmem() pri
or to the netCDF nc_open() and nc_create() calls.
int nc__create_mp(const char path[], int cmode, size_t
initialsize, int pe, size_t* chunksize, int* ncid)
Like nc__create() but allows the base PE to be set.
The argument pe sets the base PE at creation time.
Printed: 101.10.25 18 April 1997 20
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
In the MPP environment, nc__create() and
nc_create() set the base PE to processor zero by
default.
int nc__open_mp(const char path[], int mode, int pe,
size_t* chunksize, int* ncid)
Like nc__open() but allows the base PE to be set.
The argument pe sets the base PE at creation time.
In the MPP environment, nc__open() and nc_open()
set the base PE to processor zero by default.
int nc_inq_base_pe(int ncid, int* pe)
Inquires of the netCDF dataset which PE is being
used as the base for MPP use. This is safe to use
at any time.
int nc_set_base_pe(int ncid, int pe)
Resets the base PE for the netCDF dataset. Only
perform this operation when the affected communica
tor group synchronizes before and after the call.
This operation is very risky and should only be
contemplated under only the most extreme cases.
ENVIRONMENT VARIABLES
NETCDF_FFIOSPEC
Specifies the Flexible File I/O buffers for netCDF I/O
when executing under the UNICOS operating system (the
variable is ignored on other operating systems). An
appropriate specification can greatly increase the ef
ficiency of netCDF I/O -- to the extent that it can
actually surpass FORTRAN binary I/O. This environment
variable has been made a little more generalized, such
that other FFIO option specifications can now be
added. The default specification is bufa:336:2, un
less a current FFIO specification is in operation,
which will be honored. See UNICOS Flexible File I/O
for more information.
MAILING-LISTS
Both a mailing list and a digest are available for discus
sion of the netCDF interface and announcements about
netCDF bugs, fixes, and enhancements. To begin or change
your subscription to either the mailing-list or the di
gest, send one of the following in the body (not the sub
ject line) of an email message to "majordomo@unida
ta.ucar.edu". Use your email address in place of
jdoe@host.inst.domain.
To subscribe to the netCDF mailing list:
subscribe netcdfgroup jdoe@host.inst.domain
To unsubscribe from the netCDF mailing list:
Printed: 101.10.25 18 April 1997 21
NETCDF(3) UNIDATA LIBRARY FUNCTIONS NETCDF(3)
unsubscribe netcdfgroup jdoe@host.inst.domain
To subscribe to the netCDF digest:
subscribe netcdfdigest jdoe@host.inst.domain
To unsubscribe from the netCDF digest:
unsubscribe netcdfdigest jdoe@host.inst.domain
To retrieve the general introductory information for the
mailing list:
info netcdfgroup
To get a synopsis of other majordomo commands:
help
SEE ALSOncdump(1), ncgen(1), netcdf(3).
netCDF User's Guide, published by the Unidata Program Cen
ter, University Corporation for Atmospheric Research, lo
cated in Boulder, Colorado.
Printed: 101.10.25 18 April 1997 22
