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<h1 align=center>NCGEN3</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#EXAMPLES">EXAMPLES</a><br>
<a href="#USAGE">USAGE</a><br>
<a href="#BUGS">BUGS</a><br>
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<a name="NAME"></a>
<h2>NAME</h2>
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<p>ncgen3 − From a CDL file generate a netCDF classic
or 64 bit classicfile, a C program, or a Fortran program</p>
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<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
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<p>ncgen3 [-b] [-c] [-f] [-k <i>kind_of_file</i>] [-x] [-n]
[-o <i>netcdf_filename</i>] <i>input_file</i></p>
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<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
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<p><b>ncgen3</b> generates either a netCDF file, or C or
Fortran source code to create a netCDF file. The input to
<b>ncgen3</b> is a description of a netCDF file in a small
language known as CDL (network Common Data form Language),
described below. If no options are specified in invoking
<b>ncgen3</b>, it merely checks the syntax of the input CDL
file, producing error messages for any violations of CDL
syntax. Other options can be used to create the
corresponding netCDF file, to generate a C program that uses
the netCDF C interface to create the netCDF file, or to
generate a Fortran program that uses the netCDF Fortran
interface to create the same netCDF file.</p>
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<p><b>ncgen3</b> may be used with the companion program
<b>ncdump</b> to perform some simple operations on netCDF
files. For example, to rename a dimension in a netCDF file,
use <b>ncdump</b> to get a CDL version of the netCDF file,
edit the CDL file to change the name of the dimensions, and
use <b>ncgen3</b> to generate the corresponding netCDF file
from the edited CDL file.</p>
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<a name="OPTIONS"></a>
<h2>OPTIONS</h2>
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<p><b>-b</b></p>
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<p>Create a (binary) netCDF file. If the <b>-o</b> option
is absent, a default file name will be constructed from the
netCDF name (specified after the <b>netcdf</b> keyword in
the input) by appending the ‘.nc’ extension. If
a file already exists with the specified name, it will be
overwritten.</p>
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<p><b>-c</b></p>
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<p>Generate <b>C</b> source code that will create a netCDF
file matching the netCDF specification. The C source code is
written to standard output.</p>
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<p><b>-f</b></p>
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<p>Generate <b>Fortran</b> source code that will create a
netCDF file matching the netCDF specification. The Fortran
source code is written to standard output.</p>
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<p><b>-o</b> netcdf_file</p></td>
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<p>Name for the binary netCDF file created. If this option
is specified, it implies the "<b>-b</b>" option.
(This option is necessary because netCDF files cannot be
written directly to standard output, since standard output
is not seekable.)</p>
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<p><b>-k</b> kind_of_file</p></td>
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<p>Using -k2 or -k "64-bit offset" specifies that
generated file (or program) should use version 2 of format
that employs 64-bit file offsets. The default is to use
version 1 ("classic") format with 32-bit file
offsets, although this limits the size of the netCDF file,
variables, and records to the sizes supported by the classic
format. (NetCDF-4 will support additional kinds of netCDF
files, "netCDF-4" and "netCDF-4 classic
model".) Note: -v is also accepted to mean the same
thing as -k for backward compatibility, but -k is preferred,
to match the corresponding ncdump option.</p>
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<p><b>-x</b></p>
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<p>Don’t initialize data with fill values. This can
speed up creation of large netCDF files greatly, but later
attempts to read unwritten data from the generated file will
not be easily detectable.</p>
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<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
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<p>Check the syntax of the CDL file
‘<b>foo.cdl</b>’:</p></td>
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<p>ncgen3 foo.cdl</p></td>
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<p>From the CDL file ‘<b>foo.cdl</b>’, generate
an equivalent binary netCDF file named
‘<b>x.nc</b>’:</p></td>
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<p>ncgen3 -o x.nc foo.cdl</p></td>
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<p>From the CDL file ‘<b>foo.cdl</b>’, generate
a C program containing the netCDF function invocations
necessary to create an equivalent binary netCDF file named
‘<b>x.nc</b>’:</p></td>
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<p>ncgen3 -c -o x.nc foo.cdl</p></td>
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<a name="USAGE"></a>
<h2>USAGE</h2>
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<p><b>CDL Syntax Summary</b></p></td>
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<p>Below is an example of CDL syntax, describing a netCDF
file with several named dimensions (lat, lon, and time),
variables (Z, t, p, rh, lat, lon, time), variable attributes
(units, long_name, valid_range, _FillValue), and some data.
CDL keywords are in boldface. (This example is intended to
illustrate the syntax; a real CDL file would have a more
complete set of attributes so that the data would be more
completely self-describing.)</p>
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<pre><b>netcdf</b> foo { // an example netCDF specification in CDL
<b>dimensions</b>:
</pre>
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<p>lat = 10, lon = 5, time = <b>unlimited</b> ;</p>
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<p><b>variables</b>:</p></td>
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<p><b>long</b> lat(lat), lon(lon), time(time);</p>
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<p><b>float</b> Z(time,lat,lon), t(time,lat,lon);</p>
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<p><b>double</b> p(time,lat,lon);</p>
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<p><b>long</b> rh(time,lat,lon);</p>
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<p>// variable attributes</p>
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<p>lat:long_name = "latitude";</p>
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<p>lat:units = "degrees_north";</p>
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<p>lon:long_name = "longitude";</p>
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<p>lon:units = "degrees_east";</p>
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<p>time:units = "seconds since 1992-1-1
00:00:00";</p>
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<p>Z:units = "geopotential meters";</p>
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<p>Z:valid_range = 0., 5000.;</p>
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<p>p:_FillValue = -9999.;</p>
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<p>rh:_FillValue = -1;</p>
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<p><b>data</b>:</p></td>
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<p>lat = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90;</p>
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<p>lon = -140, -118, -96, -84, -52;</p>
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<p>}</p></td>
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<p>All CDL statements are terminated by a semicolon. Spaces,
tabs, and newlines can be used freely for readability.
Comments may follow the characters ‘//’ on any
line.</p>
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<p>A CDL description consists of three optional parts:
<i>dimensions</i>, <i>variables</i>, and <i>data</i>,
beginning with the keyword <b>dimensions:</b>,
<b>variables:</b>, and <b>data</b>, respectively. The
variable part may contain <i>variable declarations</i> and
<i>attribute assignments</i>.</p>
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<p>A netCDF <i>dimension</i> is used to define the shape of
one or more of the multidimensional variables contained in
the netCDF file. A netCDF dimension has a name and a size.
At most one dimension in a netCDF file can have the
<b>unlimited</b> size, which means a variable using this
dimension can grow to any length (like a record number in a
file).</p>
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<p>A <i>variable</i> represents a multidimensional array of
values of the same type. A variable has a name, a data type,
and a shape described by its list of dimensions. Each
variable may also have associated <i>attributes</i> (see
below) as well as data values. The name, data type, and
shape of a variable are specified by its declaration in the
<i>variable</i> section of a CDL description. A variable may
have the same name as a dimension; by convention such a
variable is one-dimensional and contains coordinates of the
dimension it names. Dimensions need not have corresponding
variables.</p>
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<p>A netCDF <i>attribute</i> contains information about a
netCDF variable or about the whole netCDF dataset.
Attributes are used to specify such properties as units,
special values, maximum and minimum valid values, scaling
factors, offsets, and parameters. Attribute information is
represented by single values or arrays of values. For
example, "units" is an attribute represented by a
character array such as "celsius". An attribute
has an associated variable, a name, a data type, a length,
and a value. In contrast to variables that are intended for
data, attributes are intended for metadata (data about
data).</p>
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<p>In CDL, an attribute is designated by a variable and
attribute name, separated by ‘:’. It is possible
to assign <i>global</i> attributes not associated with any
variable to the netCDF as a whole by using ‘:’
before the attribute name. The data type of an attribute in
CDL is derived from the type of the value assigned to it.
The length of an attribute is the number of data values
assigned to it, or the number of characters in the character
string assigned to it. Multiple values are assigned to
non-character attributes by separating the values with
commas. All values assigned to an attribute must be of the
same type.</p>
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<p>The names for CDL dimensions, variables, and attributes
must begin with an alphabetic character or ‘_’,
and subsequent characters may be alphanumeric or
‘_’ or ‘-’.</p>
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<p>The optional <i>data</i> section of a CDL specification
is where netCDF variables may be initialized. The syntax of
an initialization is simple: a variable name, an equals
sign, and a comma-delimited list of constants (possibly
separated by spaces, tabs and newlines) terminated with a
semicolon. For multi-dimensional arrays, the last dimension
varies fastest. Thus row-order rather than column order is
used for matrices. If fewer values are supplied than are
needed to fill a variable, it is extended with a
type-dependent ‘fill value’, which can be
overridden by supplying a value for a distinguished variable
attribute named ‘_FillValue’. The types of
constants need not match the type declared for a variable;
coercions are done to convert integers to floating point,
for example. The constant ‘_’ can be used to
designate the fill value for a variable.</p>
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<p><b>Primitive Data Types</b></p></td>
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<p><b>char</b></p>
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<p>characters</p>
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<p><b>byte</b></p>
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<p>8-bit data</p>
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<p><b>short</b></p>
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<p>16-bit signed integers</p>
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<p><b>long</b></p>
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<p>32-bit signed integers</p>
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<p><b>int</b></p>
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<p>(synonymous with <b>long</b>)</p>
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<p><b>float</b></p>
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<p>IEEE single precision floating point (32 bits)</p>
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<p><b>real</b></p>
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<p>(synonymous with <b>float</b>)</p>
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<p><b>double</b></p>
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<p>IEEE double precision floating point (64 bits)</p>
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</td>
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<p>Except for the added data-type <b>byte</b> and the lack
of <b>unsigned</b>, CDL supports the same primitive data
types as C. The names for the primitive data types are
reserved words in CDL, so the names of variables,
dimensions, and attributes must not be type names. In
declarations, type names may be specified in either upper or
lower case.</p>
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<p>Bytes differ from characters in that they are intended to
hold a full eight bits of data, and the zero byte has no
special significance, as it does for character data.
<b>ncgen3</b> converts <b>byte</b> declarations to
<b>char</b> declarations in the output C code and to the
nonstandard <b>BYTE</b> declaration in output Fortran
code.</p>
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<p>Shorts can hold values between -32768 and 32767.
<b>ncgen3</b> converts <b>short</b> declarations to
<b>short</b> declarations in the output C code and to the
nonstandard <b>INTEGER*2</b> declaration in output Fortran
code.</p>
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<p>Longs can hold values between -2147483648 and 2147483647.
<b>ncgen3</b> converts <b>long</b> declarations to
<b>long</b> declarations in the output C code and to
<b>INTEGER</b> declarations in output Fortran code.
<b>int</b> and <b>integer</b> are accepted as synonyms for
<b>long</b> in CDL declarations. Now that there are
platforms with 64-bit representations for C longs, it may be
better to use the <b>int</b> synonym to avoid confusion.</p>
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<p>Floats can hold values between about -3.4+38 and 3.4+38.
Their external representation is as 32-bit IEEE normalized
single-precision floating point numbers. <b>ncgen3</b>
converts <b>float</b> declarations to <b>float</b>
declarations in the output C code and to <b>REAL</b>
declarations in output Fortran code. <b>real</b> is accepted
as a synonym for <b>float</b> in CDL declarations.</p>
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<p>Doubles can hold values between about -1.7+308 and
1.7+308. Their external representation is as 64-bit IEEE
standard normalized double-precision floating point numbers.
<b>ncgen3</b> converts <b>double</b> declarations to
<b>double</b> declarations in the output C code and to
<b>DOUBLE PRECISION</b> declarations in output Fortran
code.</p>
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<p><b>CDL Constants</b></p></td>
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<p>Constants assigned to attributes or variables may be of
any of the basic netCDF types. The syntax for constants is
similar to C syntax, except that type suffixes must be
appended to shorts and floats to distinguish them from longs
and doubles.</p>
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<p>A <i>byte</i> constant is represented by a single
character or multiple character escape sequence enclosed in
single quotes. For example,</p></td>
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<p>’a’</p>
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<td width="7%">
</td>
<td width="7%">
<p>// ASCII ‘a’<br>
’\0’</p>
</td>
<td width="7%"></td>
<td width="49%">
</td>
<tr valign="top" align="left">
<td width="21%"></td>
<td width="5%"></td>
<td width="7%"></td>
<td width="7%">
</td>
<td width="7%">
<p>// a zero byte<br>
’\n’</p>
</td>
<td width="49%">
</td>
<tr valign="top" align="left">
<td width="21%"></td>
<td width="5%"></td>
<td width="7%"></td>
<td width="7%">
</td>
<td width="7%">
<p>// ASCII newline character<br>
’\33’</p>
</td>
<td width="49%">
</td>
<tr valign="top" align="left">
<td width="21%"></td>
<td width="5%"></td>
<td width="7%"></td>
<td width="7%">
</td>
<td width="7%">
<p>// ASCII escape character (33 octal)<br>
’\x2b’</p>
</td>
<td width="49%">
</td>
<tr valign="top" align="left">
<td width="21%"></td>
<td width="5%"></td>
<td width="7%"></td>
<td width="7%">
<p>// ASCII plus (2b hex)<br>
’\377’</p>
</td>
<td width="7%"></td>
<td width="49%">
</td>
<tr valign="top" align="left">
<td width="21%"></td>
<td width="5%"></td>
<td width="7%"></td>
<td width="7%">
<p>// 377 octal = 255 decimal, non-ASCII</p>
</td>
<td width="7%"></td>
<td width="49%">
</td>
</table>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="10%"></td>
<td width="89%">
<p>Character constants are enclosed in double quotes. A
character array may be represented as a string enclosed in
double quotes. The usual C string escape conventions are
honored. For example</p></td>
</table>
<!-- TABS -->
<table width="100%" border=0 rules="none" frame="void"
cols="6" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="7%">
<p>"a"</p>
</td>
<td width="7%">
</td>
<td width="7%">
<p>// ASCII ‘a’</p>
</td>
<td width="7%"></td>
<td width="49%">
</td>
<tr valign="top" align="left">
<td width="20%"></td>
<td width="7%">
<p>"Two\nlines\n"</p>
</td>
<td width="7%"></td>
<td width="7%"></td>
<td width="7%">
<p>// a 10-character string with two embedded newlines</p>
</td>
<td width="49%">
</td>
<tr valign="top" align="left">
<td width="20%"></td>
<td width="7%">
<p>"a bell:\007"</p>
</td>
<td width="7%"></td>
<td width="7%"></td>
<td width="7%">
<p>// a string containing an ASCII bell</p>
</td>
<td width="49%">
</td>
</table>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="10%"></td>
<td width="89%">
<p>Note that the netCDF character array "a" would
fit in a one-element variable, since no terminating NULL
character is assumed. However, a zero byte in a character
array is interpreted as the end of the significant
characters by the <b>ncdump</b> program, following the C
convention. Therefore, a NULL byte should not be embedded in
a character string unless at the end: use the <i>byte</i>
data type instead for byte arrays that contain the zero
byte. NetCDF and CDL have no string type, but only
fixed-length character arrays, which may be
multi-dimensional.</p>
<!-- INDENTATION -->
<p><i>short</i> integer constants are intended for
representing 16-bit signed quantities. The form of a
<i>short</i> constant is an integer constant with an
‘s’ or ‘S’ appended. If a
<i>short</i> constant begins with ‘0’, it is
interpreted as octal, except that if it begins with
‘0x’, it is interpreted as a hexadecimal
constant. For example:</p></td>
</table>
<!-- TABS -->
<table width="100%" border=0 rules="none" frame="void"
cols="5" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="7%">
<p>-2s</p>
</td>
<td width="7%">
<p>// a short -2</p>
</td>
<td width="7%"></td>
<td width="57%">
</td>
<tr valign="top" align="left">
<td width="20%"></td>
<td width="7%">
<p>0123s</p>
</td>
<td width="7%"></td>
<td width="7%">
<p>// octal</p>
</td>
<td width="57%">
</td>
</table>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="79%">
<p>0x7ffs //hexadecimal</p></td>
</table>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="10%"></td>
<td width="89%">
<p><i>Long</i> integer constants are intended for
representing 32-bit signed quantities. The form of a
<i>long</i> constant is an ordinary integer constant,
although it is acceptable to append an optional
‘l’ or ‘L’. If a <i>long</i>
constant begins with ‘0’, it is interpreted as
octal, except that if it begins with ‘0x’, it is
interpreted as a hexadecimal constant. Examples of valid
<i>long</i> constants include:</p></td>
</table>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="79%">
<pre>-2
1234567890L
</pre>
</td>
</table>
<!-- TABS -->
<table width="100%" border=0 rules="none" frame="void"
cols="6" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="7%">
<p>0123</p>
</td>
<td width="7%">
</td>
<td width="7%">
<p>// octal</p>
</td>
<td width="7%"></td>
<td width="49%">
</td>
<tr valign="top" align="left">
<td width="20%"></td>
<td width="7%">
<p>0x7ff</p>
</td>
<td width="7%"></td>
<td width="7%">
</td>
<td width="7%">
<p>// hexadecimal</p>
</td>
<td width="49%">
</td>
</table>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="10%"></td>
<td width="89%">
<p>Floating point constants of type <i>float</i> are
appropriate for representing floating point data with about
seven significant digits of precision. The form of a
<i>float</i> constant is the same as a C floating point
constant with an ‘f’ or ‘F’
appended. For example the following are all acceptable
<i>float</i> constants:</p></td>
</table>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="79%">
<pre>-2.0f
</pre>
</td>
</table>
<!-- TABS -->
<table width="100%" border=0 rules="none" frame="void"
cols="5" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="7%">
<p>3.14159265358979f</p>
</td>
<td width="22%"></td>
<td width="7%">
<p>// will be truncated to less precision</p>
</td>
<td width="42%">
</td>
</table>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="79%">
<p>1.f</p></td>
</table>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="10%"></td>
<td width="89%">
<p>Floating point constants of type <i>double</i> are
appropriate for representing floating point data with about
sixteen significant digits of precision. The form of a
<i>double</i> constant is the same as a C floating point
constant. An optional ‘d’ or ‘D’ may
be appended. For example the following are all acceptable
<i>double</i> constants:</p></td>
</table>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="79%">
<pre>-2.0
3.141592653589793
1.0e-20
1.d
</pre>
</td>
</table>
<a name="BUGS"></a>
<h2>BUGS</h2>
<!-- INDENTATION -->
<table width="100%" border=0 rules="none" frame="void"
cols="2" cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="10%"></td>
<td width="89%">
<p>The programs generated by <b>ncgen3</b> when using the
<b>-c</b> or <b>-f</b> use initialization statements to
store data in variables, and will fail to produce compilable
programs if you try to use them for large datasets, since
the resulting statements may exceed the line length or
number of continuation statements permitted by the
compiler.</p>
<!-- INDENTATION -->
<p>The CDL syntax makes it easy to assign what looks like an
array of variable-length strings to a netCDF variable, but
the strings will simply be concatenated into a single array
of characters, since netCDF cannot represent an array of
variable-length strings in one netCDF variable.</p>
<!-- INDENTATION -->
<p>NetCDF and CDL do not yet support a type corresponding to
a 64-bit integer.</p>
</td>
</table>
<hr>
</body>
</html>
