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Programming in C
Introduction
This section is dedicated to programmers who want to write applications
(or service routines) in the ANSI C programming language. Since the GIPSY
programming environment supports both Fortran and C as programming
languages, there are some restrictions on what type of arguments may be
passed to the routines. Also the module names have some
restrictions since each operating system interfaces C and Fortran
differently.
Function Arguments and Names
Each operating system has different ideas about how to interface Fortran
modules with C modules. Therefore a portable
Fortran to C (and vice
versa) interface was developed at the Kapteyn Institute.
This interface sets a number of
restraints on the types of arguments passed to other service
routines and on the names of servant routines.
Module names
Almost any routine in the GIPSY library is both C callable and Fortran
callable. C programmers append `_c' to the lower case Fortran name.
For example, a Fortran task would start with
`CALL INIT', and a C task with `init_c();'.
Argument Types
The types of arguments which may be passed from one routine to the
other, whether the called routines are written in C or Fortran, are:
Fortran C
----------------- ------
CHARACTER fchar
COMPLEX complex
DOUBLE PRECISION double
INTEGER fint
LOGICAL bool
REAL float
The non-C types in this table are all defined in include file
gipsyc.h, so
each C program or function must include this file (after the standard
C include files but before the definition files).
fint
A fint is an integer which has the same number of bytes as the
Fortran integer. Since C supports three integer types
(short, int,
long) and since the number of bytes occupied by these types is system
dependent, C programmers must use fint for portability reasons.
fint will be one of the following, depending on the operating system:
typedef short fint;
typedef int fint;
typedef long fint;
bool
A bool is also an integer which has the same number of bytes as
the Fortran logical.
complex
A complex is a struct consisting of two floats, one carrying the
real part, the second carrying the imaginary part.
typedef struct { float r; float i; } complex;
fchar
An fchar is a struct equivalent to a Fortran character variable or
constant. fchar carries the address of the first element of the
string and the length of the string. Note that this string is
not null-terminated!
typedef struct { char *a; fint l; } fchar;
Function types
The Fortran routines which correspond with C functions are the
following:
Fortran C
----------------------- -------------------------
SUBROUTINE SS(..) void ss_c(..)
CHARACTER*(*) CC(..) void cc_c(fchar r,..)
COMPLEX CX(..) complex cx_c(..)
DOUBLE PRECISION DD(..) double dd_c(..)
INTEGER II(..) fint ii_c(..)
LOGICAL LL(..) bool ll_c(..)
REAL RR(..) float rr_c(..)
Note that Fortran character functions become voids in C with an extra
argument being the destination of the character function.
Standard C library
Although most operating systems support ANSI C, some of them don't have the
standard C include files and libraries. Therefore the eXtended C
library was developed at the Kapteyn Institute to add the most
important missing functions, or to replace those which are available on
the operation systems but not working according to ANSI C
specifications.
We have tried to supply the C programmer with the most
interesting of those functions. These functions are defined in the
following ANSI C include files.
Note that these include files reside
in $gip_inc, and that they must be included using the
"" notation instead of <>.