Ubuntu Manpage: NCAR Graphics C-binding - Description of how to use the NCAR Graphics C-binding.

NAME

       NCAR Graphics C-binding - Description of how to use the NCAR Graphics C-binding.

SYNOPSIS

       The  NCAR  Graphics C-binding consists of a collection of C routines that allow you to call NCAR Graphics
       Fortran routines from a C program without having to worry about the C to Fortran interface yourself.  For
       detailed  information  about  the  C-binding  for  a  particular routine, please see the man page for the
       corresponding Fortran routine.

       A C-binding has been created for every user entry point in the NCAR Graphics utilities with the exception
       of  some  of  the  obsolete utilities listed below.  A GKS level 0A C-binding has also been created which
       adheres to the ISO/IEC standard.

       From here on, a utility C-binding refers to a C-binding for the NCAR Graphics utilities (AREAS,  CONPACK,
       etc.).

NAMING CONVENTION

       For  all  of the utility user entry points, the name of the C-binding function is the same as the Fortran
       routine name with a "c_" prepended.  For example, the name of  the  C-binding  for  the  CONPACK  routine
       CPBACK is c_cpback.  This naming convention does not apply to the GKS C-bindings.  Instead, the C-binding
       names are more descriptive, like gset_fill_colr_ind which is equivalent to the  Fortran  routine  GSFACI.
       Please  see  the  man  page  for  ncarg_gks_cbind(3NCARG)  the GKS Fortran routine to get the name of the
       corresponding GKS C-binding name.

       The C programming language is case sensitive, so for convenience the utility C-binding  names  and  their
       arguments  are  all  in  lower  case.  In this man page, the Fortran routines and their arguments will be
       referred to in upper-case.

ARGUMENT LISTS

       The argument list of each utility C-binding corresponds with  the  argument  list  of  the  corresponding
       Fortran  routine  except  in  some  cases  where  multi-dimensioned  arrays  and/or character strings are
       involved.  These exceptions will be described in separate sections.

       The C-binding argument list being similar to the Fortran argument list makes using the C-bindings  easier
       for  people who already know the calling sequence of a particular Fortran routine.  For example, the NCAR
       Graphics routine PLCHHQ has the following argument list:

       PLCHHQ(REAL X, REAL Y, CHARACTER CHRS, REAL SZ, REAL ANG, REAL CNTR)

       and the corresponding C-binding c_plchhq has the same type of argument list:

       c_plchhq(float x, float y, char *chrs, float sz, float ang, float cntr)

ARRAYS

One of the exceptions to the utility C-binding argument lists has to do with multi-dimensioned arrays.
In Fortran, arrays are stored in column-major order, while in C they are stored in row-major order. This
means that the subscripts of a multi-dimensioned array need to be switched before passing the array to a
Fortran routine from C.

As an example, the CONPACK routine CPRECT takes as one of its arguments a two-dimensional array, ZDAT.
If the Fortran dimensions of ZDAT are to be 25 x 14, then in the C program you must dimension ZDAT to be
14 x 25 before calling the C-binding c_cprect. The next three arguments of CPRECT describe the array in
question. The first of these three arguments, KZDT, is the first dimension of the array ZDAT as it is
declared in the Fortran calling program. For CPRECT this value would be 25. For the C-binding c_cprect,
however, this argument is the second dimension of the array as declared in the C program. This value
would be 25 as well since the subscripts had to be switched in the C program. The second and third of
these three arguments (MZDT and NZDT) specify the number of elements in each row and column
(respectively) to be contoured. If you only want to contour 20 x 10 of the array ZDAT, then MZDT and
NZDT should be 20 and 10 respectively in CPRECT. For c_cprect, these variables specify the columns and
rows, so again, the values would be 20 and 10 (because the subscripts have to be switched).

CHARACTER STRINGS

       Another  exception  to  the argument lists for the utility C-bindings has to do with routines that return
       character strings.  The NCAR Graphics routines that return strings through the parameter list do not have
       a  string  length  as  part  of their argument lists, so you must pass an extra argument to the C-binding
       which specifies the maximum length of the string.  Also, all input strings passed to the C-bindings  must
       be null-terminated!

       For  example, in the routine PCGETC, you pass a parameter name and it returns the value of that parameter
       which in this case is a string.  The two arguments to PCGETC  are  WHCH  and  CVAL,  where  WHCH  is  the
       parameter  name  and  CVAL  is the string to be returned.  Since the C-binding c_pcgetc needs to know the
       length of cval, an extra argument of type "int" must be passed.  Thus, the arguments for  c_pcgetc  would
       be  whch, cval, and len, where len is the length of cval as it is declared in the C program.  In any case
       of having to add an extra argument for the string length, the extra argument will always be the last  one
       in the list.  If more than one string length argument needs to be added, then each one should be added at
       the end of the argument list in the order that their corresponding strings appear.

       There are some routines like AGDSHN which are defined as character strings themselves.  In this case, the
       user does not need to pass a string length since it is already defined.  But, the string that is returned
       is declared statically, thus it will go away once you call the routine again.  If you need to save  these
       character strings, be sure to copy them to your own local variable.

FUNCTION PROTOTYPES

       The  C-bindings  are  intended  to  be  ANSI C compliant.  To get the correct function prototypes for the
       utility C-bindings, you can include <ncarg/ncargC.h>.  For the GKS C-bindings, include <ncarg/gks.h>.  In
       some cases, it may be necessary to typecast the arguments in the utility C-bindings to get the prototypes
       correct.  For example, the C-bindings do not distinguish between singly and multiply dimensioned  arrays,
       so  if  you are passing a multiply dimensioned float array, you may need to typecast it as a (float *) if
       this is not how it is declared in the main program.

COMPILING YOUR PROGRAM

       To compile your NCAR Graphics C program with the C-bindings, use the NCARG application ncargcc.   ncargcc
       will  take  care of loading in the necessary C/Fortran interface libraries as well as the NCAR Graphics C
       and Fortran libraries.  You will either need to set the  NCARG_ROOT  or  the  NCARG_BIN,  NCARG_LIB,  and
       NCARG_INCLUDE environment variables in order to run ncargcc.  See "man ncargintro" for more information.

       If  you  do not wish to use ncargcc, then you can just run it with no arguments to see what the necessary
       libraries are, and then put this information in your Makefile or whatever else you are using  to  compile
       and  link your program.  Note:  if you have an ANSI C compiler, it is important that you define the macro
       NeedFuncProto on the compile line so that function prototyping is included.

EXAMPLES

       A few examples of C programs that  call  the  NCAR  Graphics  C-bindings  have  been  provided  for  your
       convenience.   You  may  be familiar with the output from these C programs as they were modeled after the
       Fortran programs that you can get with the ncargex command.  To copy any one of these C programs in  your
       directory, and then compile, link, and run it, type:

       ncargex xxxx

       where xxxx is the name of the example you wish to generate.  To see a list of all the C examples, type:

     ncargex -C -list

ncargex uses ncargcc to compile and link the C-binding example programs.

OBSOLETE ROUTINES

       C-bindings have not been provided for user entry points in the following obsolete utilities:

     Conran_family, Conrec_family, Halftone, Isosrfhr, and Pwrite_family.

COPYRIGHT

       Copyright (C) 1987-2002
       University Corporation for Atmospheric Research

       The use of this Software is governed by a License Agreement.