Provided by: netcdf-bin_4.6.2-1build1_amd64 bug

NAME

       ncgen3  - From a CDL file generate a netCDF classic or 64 bit classicfile, a C program, or
       a Fortran program

SYNOPSIS

       ncgen3 [-b] [-c] [-f] [-k kind_of_file] [-x] [-n] [-o netcdf_filename] input_file

DESCRIPTION

       ncgen3 generates either a netCDF file, or C or Fortran source  code  to  create  a  netCDF
       file.   The input to ncgen3 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  ncgen3,  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.

       ncgen3  may be used with the companion program ncdump to perform some simple operations on
       netCDF files.  For example, to rename a dimension in a netCDF file, use ncdump  to  get  a
       CDL  version  of  the netCDF file, edit the CDL file to change the name of the dimensions,
       and use ncgen3 to generate the corresponding netCDF file from the edited CDL file.

OPTIONS

       -b     Create a (binary) netCDF file.  If the -o option is absent,  a  default  file  name
              will be constructed from the netCDF name (specified after the netcdf keyword in the
              input) by appending the `.nc'  extension.   If  a  file  already  exists  with  the
              specified name, it will be overwritten.

       -c     Generate  C  source  code  that  will  create  a  netCDF  file  matching the netCDF
              specification.  The C source code is written to standard output.

       -f     Generate Fortran source code that will create a netCDF  file  matching  the  netCDF
              specification.  The Fortran source code is written to standard output.

       -o netcdf_file
              Name  for  the binary netCDF file created.  If this option is specified, it implies
              the "-b" option.  (This option is necessary because netCDF files cannot be  written
              directly to standard output, since standard output is not seekable.)

       -k kind_of_file
              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.

       -x     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.

EXAMPLES

       Check the syntax of the CDL file `foo.cdl':

              ncgen3 foo.cdl

       From the CDL file `foo.cdl', generate an equivalent binary netCDF file named `x.nc':

              ncgen3 -o x.nc foo.cdl

       From the CDL  file  `foo.cdl',  generate  a  C  program  containing  the  netCDF  function
       invocations necessary to create an equivalent binary netCDF file named `x.nc':

              ncgen3 -c -o x.nc foo.cdl

USAGE

   CDL Syntax Summary
       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.)

              netcdf foo {  // an example netCDF specification in CDL

              dimensions:
                   lat = 10, lon = 5, time = unlimited ;

              variables:
                   long    lat(lat), lon(lon), time(time);
                   float   Z(time,lat,lon), t(time,lat,lon);
                   double  p(time,lat,lon);
                   long    rh(time,lat,lon);

                   // variable attributes
                   lat:long_name = "latitude";
                   lat:units = "degrees_north";
                   lon:long_name = "longitude";
                   lon:units = "degrees_east";
                   time:units = "seconds since 1992-1-1 00:00:00";
                   Z:units = "geopotential meters";
                   Z:valid_range = 0., 5000.;
                   p:_FillValue = -9999.;
                   rh:_FillValue = -1;

              data:
                   lat   = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90;
                   lon   = -140, -118, -96, -84, -52;
              }

       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.

       A CDL description consists of three  optional  parts:  dimensions,  variables,  and  data,
       beginning  with the keyword dimensions:, variables:, and data, respectively.  The variable
       part may contain variable declarations and attribute assignments.

       A netCDF dimension 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 unlimited size, which  means  a  variable
       using this dimension can grow to any length (like a record number in a file).

       A variable 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 attributes (see below) as well as data values.  The name, data type,
       and shape of a variable are specified by its declaration in the variable 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.

       A  netCDF attribute 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).

       In CDL, an attribute is designated by a variable and attribute name, separated by `:'.  It
       is possible to assign global 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.

       The  names  for  CDL  dimensions,  variables, and attributes must begin with an alphabetic
       character or `_', and subsequent characters may be alphanumeric or `_' or `-'.

       The optional data 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.

   Primitive Data Types
              char characters
              byte 8-bit data
              short     16-bit signed integers
              long 32-bit signed integers
              int  (synonymous with long)
              float     IEEE single precision floating point (32 bits)
              real (synonymous with float)
              double    IEEE double precision floating point (64 bits)

       Except  for  the  added  data-type  byte  and  the lack of unsigned, 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.

       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.  ncgen3
       converts byte declarations  to  char  declarations  in  the  output  C  code  and  to  the
       nonstandard BYTE declaration in output Fortran code.

       Shorts  can  hold  values between -32768 and 32767.  ncgen3 converts short declarations to
       short declarations in the output C code and to the nonstandard  INTEGER*2  declaration  in
       output Fortran code.

       Longs   can  hold  values  between  -2147483648  and  2147483647.   ncgen3  converts  long
       declarations to long declarations in the output C code  and  to  INTEGER  declarations  in
       output  Fortran  code.   int  and  integer  are  accepted  as  synonyms  for  long  in CDL
       declarations.  Now that there are platforms with 64-bit representations for  C  longs,  it
       may be better to use the int synonym to avoid confusion.

       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.  ncgen3 converts  float
       declarations to float declarations in the output C code and to REAL declarations in output
       Fortran code.  real is accepted as a synonym for float in CDL declarations.

       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.  ncgen3
       converts double declarations to double declarations in the output C  code  and  to  DOUBLE
       PRECISION declarations in output Fortran code.

   CDL Constants
       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.

       A byte constant is represented by a single character or multiple character escape sequence
       enclosed in single quotes.  For example,
               'a'      // ASCII `a'
               '\0'          // a zero byte
               '\n'          // ASCII newline character
               '\33'         // ASCII escape character (33 octal)
               '\x2b'   // ASCII plus (2b hex)
               '\377'   // 377 octal = 255 decimal, non-ASCII

       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
              "a"       // ASCII `a'
              "Two\nlines\n" // a 10-character string with two embedded newlines
              "a bell:\007"  // a string containing an ASCII bell
       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 ncdump program, following  the
       C  convention.  Therefore, a NULL byte should not be embedded in a character string unless
       at the end: use the byte 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.

       short integer constants are intended for representing 16-bit signed quantities.  The  form
       of  a  short  constant  is  an  integer  constant with an `s' or `S' appended.  If a short
       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:
              -2s  // a short -2
              0123s     // octal
              0x7ffs  //hexadecimal

       Long  integer  constants are intended for representing 32-bit signed quantities.  The form
       of a long constant is an ordinary integer constant, although it is acceptable to append an
       optional  `l'  or  `L'.   If  a long 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 long constants include:
              -2
              1234567890L
              0123      // octal
              0x7ff          // hexadecimal

       Floating  point  constants  of  type float are appropriate for representing floating point
       data with about seven significant digits of precision.  The form of a  float  constant  is
       the  same  as  a  C  floating point constant with an `f' or `F' appended.  For example the
       following are all acceptable float constants:
              -2.0f
              3.14159265358979f   // will be truncated to less precision
              1.f

       Floating point constants of type double are appropriate for  representing  floating  point
       data with about sixteen significant digits of precision.  The form of a double 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 double constants:
              -2.0
              3.141592653589793
              1.0e-20
              1.d

BUGS

       The  programs generated by ncgen3 when using the -c or -f 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.

       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.

       NetCDF and CDL do not yet support a type corresponding to a 64-bit integer.