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cfortran.doc
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cfortran.doc 4.3 */
www-zeus.desy.de/~burow OR anonymous ftp@zebra.desy.de
Burkhard Burow burow@desy.de 1990 - 1998.
cfortran.h : Interfacing C or C++ and FORTRAN
Supports: Alpha and VAX VMS, Alpha OSF, DECstation and VAX Ultrix, IBM RS/6000,
Silicon Graphics, Sun, CRAY, Apollo, HP9000, LynxOS, Convex, Absoft,
f2c, g77, NAG f90, PowerStation Fortran with Visual C++, NEC SX-4,
Portland Group.
C and C++ are generally equivalent as far as cfortran.h is concerned.
Unless explicitly noted otherwise, mention of C implicitly includes C++.
C++ compilers tested include:
SunOS> CC +p +w # Clean compiles.
IRIX> CC # Clean compiles.
IRIX> CC -fullwarn # Still some warnings to be overcome.
GNU> g++ -Wall # Compiles are clean, other than warnings for unused
# cfortran.h static routines.
N.B.: The best documentation on interfacing C or C++ and Fortran is in
the chapter named something like 'Interfacing C and Fortran'
to be found in the user's guide of almost every Fortran compiler.
Understanding this information for one or more Fortran compilers
greatly clarifies the aims and actions of cfortran.h.
Such a chapter generally also addresses issues orthogonal to cfortran.h,
for example the order of array indices, the index of the first element,
as well as compiling and linking issues.
0 Short Summary of the Syntax Required to Create the Interface
--------------------------------------------------------------
e.g. Prototyping a FORTRAN subroutine for C:
/* PROTOCCALLSFSUBn is optional for C, but mandatory for C++. */
PROTOCCALLSFSUB2(SUB_NAME,sub_name,STRING,PINT)
#define SUB_NAME(A,B) CCALLSFSUB2(SUB_NAME,sub_name,STRING,PINT, A,B)
^ - -
number of arguments _____| | STRING BYTE PBYTE BYTEV(..)|
/ | STRINGV DOUBLE PDOUBLE DOUBLEV(..)|
/ | PSTRING FLOAT PFLOAT FLOATV(..)|
types of arguments ____ / | PNSTRING INT PINT INTV(..)|
\ | PPSTRING LOGICAL PLOGICAL LOGICALV(..)|
\ | PSTRINGV LONG PLONG LONGV(..)|
\ | ZTRINGV SHORT PSHORT SHORTV(..)|
| PZTRINGV ROUTINE PVOID SIMPLE |
- -
e.g. Prototyping a FORTRAN function for C:
/* PROTOCCALLSFFUNn is mandatory for both C and C++. */
PROTOCCALLSFFUN1(INT,FUN_NAME,fun_name,STRING)
#define FUN_NAME(A) CCALLSFFUN1(FUN_NAME,fun_name,STRING, A)
e.g. calling FUN_NAME from C: {int a; a = FUN_NAME("hello");}
e.g. Creating a FORTRAN-callable wrapper for
a C function returning void, with a 7 dimensional integer array argument:
[Not supported from C++.]
FCALLSCSUB1(csub_name,CSUB_NAME,csub_name,INTVVVVVVV)
e.g. Creating a FORTRAN-callable wrapper for other C functions:
FCALLSCFUN1(STRING,cfun_name,CFUN_NAME,cfun_name,INT)
[ ^-- BYTE, DOUBLE, FLOAT, INT, LOGICAL, LONG, SHORT, VOID
are other types returned by functions. ]
e.g. COMMON BLOCKs:
FORTRAN: common /fcb/ v,w,x
character *(13) v, w(4), x(3,2)
C:
typedef struct { char v[13],w[4][13],x[2][3][13]; } FCB_DEF;
#define FCB COMMON_BLOCK(FCB,fcb)
COMMON_BLOCK_DEF(FCB_DEF,FCB);
FCB_DEF FCB; /* Define, i.e. allocate memory, in exactly one *.c file. */
e.g. accessing FCB in C: printf("%.13s",FCB.v);
I Introduction
--------------
cfortran.h is an easy-to-use powerful bridge between C and FORTRAN.
It provides a completely transparent, machine independent interface between
C and FORTRAN routines (= subroutines and/or functions) and global data,
i.e. structures and COMMON blocks.
The complete cfortran.h package consists of 4 files: the documentation in
cfortran.doc, the engine cfortran.h, examples in cfortest.c and
cfortex.f/or. [cfortex.for under VMS, cfortex.f on other machines.]
The cfortran.h package continues to be developed. The most recent version is
available via www at http://www-zeus.desy.de/~burow
or via anonymous ftp at zebra.desy.de (131.169.2.244).
The examples may be run using one of the following sets of instructions:
N.B. Unlike earlier versions, cfortran.h 3.0 and later versions
automatically uses the correct ANSI ## or pre-ANSI /**/
preprocessor operator as required by the C compiler.
N.B. As a general rule when trying to determine how to link C and Fortran,
link a trivial Fortran program using the Fortran compilers verbose option,
in order to see how the Fortran compiler drives the linker. e.g.
unix> cat f.f
END
unix> f77 -v f.f
.. lots of info. follows ...
N.B. If using a C main(), i.e. Fortran PROGRAM is not entry of the executable,
and if the link bombs with a complaint about
a missing "MAIN" (e.g. MAIN__, MAIN_, f90_main or similar),
then Fortran has hijacked the entry point to the executable
and wishes to call the rest of the executable via "MAIN".
This can usually be satisfied by doing e.g. 'cc -Dmain=MAIN__ ...'
but often kills the command line arguments in argv and argc.
The f77 verbose option, usually -v, may point to a solution.
RS/6000> # Users are strongly urged to use f77 -qextname and cc -Dextname
RS/6000> # Use -Dextname=extname if extname is a symbol used in the C code.
RS/6000> xlf -c -qextname cfortex.f
RS/6000> cc -c -Dextname cfortest.c
RS/6000> xlf -o cfortest cfortest.o cfortex.o && cfortest
DECFortran> #Only DECstations with DECFortran for Ultrix RISC Systems.
DECFortran> cc -c -DDECFortran cfortest.c
DECFortran> f77 -o cfortest cfortest.o cfortex.f && cfortest
IRIX xxxxxx 5.2 02282015 IP20 mips
MIPS> # DECstations and Silicon Graphics using the MIPS compilers.
MIPS> cc -o cfortest cfortest.c cfortex.f -lI77 -lU77 -lF77 && cfortest
MIPS> # Can also let f77 drive linking, e.g.
MIPS> cc -c cfortest.c
MIPS> f77 -o cfortest cfortest.o cfortex.f && cfortest
Apollo> # Some 'C compiler 68K Rev6.8' break. [See Section II o) Notes: Apollo]
Apollo> f77 -c cfortex.f && cc -o cfortest cfortest.c cfortex.o && cfortest
VMS> define lnk$library sys$library:vaxcrtl
VMS> cc cfortest.c
VMS> fortran cfortex.for
VMS> link/exec=cfortest cfortest,cfortex
VMS> run cfortest
OSF1 xxxxxx V3.0 347 alpha
Alpha/OSF> # Probably better to let cc drive linking, e.g.
Alpha/OSF> f77 -c cfortex.f
Alpha/OSF> cc -o cfortest cfortest.c cfortex.o -lUfor -lfor -lFutil -lots -lm
Alpha/OSF> cfortest
Alpha/OSF> # Else may need 'cc -Dmain=MAIN__' to let f77 drive linking.
Sun> # Some old cc(1) need a little help. [See Section II o) Notes: Sun]
Sun> f77 -o cfortest cfortest.c cfortex.f -lc -lm && cfortest
Sun> # Some older f77 may require 'cc -Dmain=MAIN_'.
CRAY> cft77 cfortex.f
CRAY> cc -c cfortest.c
CRAY> segldr -o cfortest.e cfortest.o cfortex.o
CRAY> ./cfortest.e
NEC> cc -c -Xa cfortest.c
NEC> f77 -o cfortest cfortest.o cfortex.f && cfortest
VAX/Ultrix/cc> # For cc on VAX Ultrix only, do the following once to cfortran.h.
VAX/Ultrix/cc> mv cfortran.h cftmp.h && grep -v "^#pragma" <cftmp.h >cfortran.h
VAX/Ultrix/f77> # In the following, 'CC' is either 'cc' or 'gcc -ansi'. NOT'vcc'
VAX/Ultrix/f77> CC -c -Dmain=MAIN_ cfortest.c
VAX/Ultrix/f77> f77 -o cfortest cfortex.f cfortest.o && cfortest
LynxOS> # In the following, 'CC' is either 'cc' or 'gcc -ansi'.
LynxOS> # Unfortunately cc is easily overwhelmed by cfortran.h,
LynxOS> # and won't compile some of the cfortest.c demos.
LynxOS> f2c -R cfortex.f
LynxOS> CC -Dlynx -o cfortest cfortest.c cfortex.c -lf2c && cfortest
HP9000> # Tested with HP-UX 7.05 B 9000/380 and with A.08.07 A 9000/730
HP9000> # CC may be either 'c89 -Aa' or 'cc -Aa'
HP9000> # Depending on the compiler version, you may need to include the
HP9000> # option '-tp,/lib/cpp' or worse, you'll have to stick to the K&R C.
HP9000> # [See Section II o) Notes: HP9000]
HP9000> # Users are strongly urged to use f77 +ppu and cc -Dextname
HP9000> # Use -Dextname=extname if extname is a symbol used in the C code.
HP9000> CC -Dextname -c cfortest.c
HP9000> f77 +ppu cfortex.f -o cfortest cfortest.o && cfortest
HP9000> # Older f77 may need
HP9000> f77 -c cfortex.f
HP9000> CC -o cfortest cfortest.c cfortex.o -lI77 -lF77 && cfortest
HP9000> # If old-style f77 +800 compiled objects are required:
HP9000> # #define hpuxFortran800
HP9000> cc -c -Aa -DhpuxFortran800 cfortest.c
HP9000> f77 +800 -o cfortest cfortest.o cfortex.f
f2c> # In the following, 'CC' is any C compiler.
f2c> f2c cfortex.f
f2c> CC -o cfortest -Df2cFortran cfortest.c cfortex.c -lf2c && cfortest
Portland Group $ # Presumably other C compilers also work.
Portland Group $ pgcc -DpgiFortran -c cfortest.c
Portland Group $ pgf77 -o cfortest cfortex.f cfortest.o && cfortest
NAGf90> # cfortex.f is distributed with Fortran 77 style comments.
NAGf90> # To convert to f90 style comments do the following once to cfortex.f:
NAGf90> mv cfortex.f cf_temp.f && sed 's/^C/\!/g' cf_temp.f > cfortex.f
NAGf90> # In the following, 'CC' is any C compiler.
NAGf90> CC -c -DNAGf90Fortran cfortest.c
NAGf90> f90 -o cfortest cfortest.o cfortex.f && cfortest
PC> # On a PC with PowerStation Fortran and Visual_C++
PC> cl /c cftest.c
PC> fl32 cftest.obj cftex.for
GNU> # GNU Fortran
GNU> # See Section VI caveat on using 'gcc -traditional'.
GNU> gcc -ansi -Wall -O -c -Df2cFortran cfortest.c
GNU> g77 -ff2c -o cfortest cfortest.o cfortex.f && cfortest
AbsoftUNIX> # Absoft Fortran for all UNIX based operating systems.
AbsoftUNIX> # e.g. Linux or Next on Intel or Motorola68000.
AbsoftUNIX> # Absoft f77 -k allows Fortran routines to be safely called from C.
AbsoftUNIX> gcc -ansi -Wall -O -c -DAbsoftUNIXFortran cfortest.c
AbsoftUNIX> f77 -k -o cfortest cfortest.o cfortex.f && cfortest
AbsoftPro> # Absoft Pro Fortran for MacOS
AbsoftPro> # Use #define AbsoftProFortran
CLIPPER> # INTERGRAPH CLIX using CLIPPER C and Fortran compilers.
CLIPPER> # N.B. - User, not cfortran.h, is responsible for
CLIPPER> # f77initio() and f77uninitio() if required.
CLIPPER> # - LOGICAL values are not mentioned in CLIPPER doc.s,
CLIPPER> # so they may not yet be correct in cfortran.h.
CLIPPER> # - K&R mode (-knr or Ac=knr) breaks FLOAT functions
CLIPPER> # (see CLIPPER doc.s) and cfortran.h does not fix it up.
CLIPPER> # [cfortran.h ok for old sun C which made the same mistake.]
CLIPPER> acc cfortest.c -c -DCLIPPERFortran
CLIPPER> af77 cfortex.f cfortest.o -o cfortest
By changing the SELECTion ifdef of cfortest.c and recompiling one can try out
a few dozen different few-line examples.
The benefits of using cfortran.h include:
1. Machine/OS/compiler independent mixing of C and FORTRAN.
2. Identical (within syntax) calls across languages, e.g.
C FORTRAN
CALL HBOOK1(1,'pT spectrum of pi+',100,0.,5.,0.)
/* C*/
HBOOK1(1,"pT spectrum of pi+",100,0.,5.,0.);
3. Each routine need only be set up once in its lifetime. e.g.
/* Setting up a FORTRAN routine to be called by C.
ID,...,VMX are merely the names of arguments.
These tags must be unique w.r.t. each other but are otherwise arbitrary. */
PROTOCCALLSFSUB6(HBOOK1,hbook1,INT,STRING,INT,FLOAT,FLOAT,FLOAT)
#define HBOOK1(ID,CHTITLE,NX,XMI,XMA,VMX) \
CCALLSFSUB6(HBOOK1,hbook1,INT,STRING,INT,FLOAT,FLOAT,FLOAT, \
ID,CHTITLE,NX,XMI,XMA,VMX)
4. Source code is NOT required for the C routines exported to FORTRAN, nor for
the FORTRAN routines imported to C. In fact, routines are most easily
prototyped using the information in the routines' documentation.
5. Routines, and the code calling them, can be coded naturally in the language
of choice. C routines may be coded with the natural assumption of being
called only by C code. cfortran.h does all the required work for FORTRAN
code to call C routines. Similarly it also does all the work required for C
to call FORTRAN routines. Therefore:
- C programmers need not embed FORTRAN argument passing mechanisms into
their code.
- FORTRAN code need not be converted into C code. i.e. The honed and
time-honored FORTRAN routines are called by C.
6. cfortran.h is a single ~1700 line C include file; portable to most
remaining, if not all, platforms.
7. STRINGS and VECTORS of STRINGS along with the usual simple arguments to
routines are supported as are functions returning STRINGS or numbers. Arrays
of pointers to strings and values of structures as C arguments, will soon be
implemented. After learning the machinery of cfortran.h, users can expand
it to create custom types of arguments. [This requires no modification to
cfortran.h, all the preprocessor directives required to implement the
custom types can be defined outside cfortran.h]
8. cfortran.h requires each routine to be exported to be explicitly set up.
While is usually only be done once in a header file it would be best if
applications were required to do no work at all in order to cross languages.
cfortran.h's simple syntax could be a convenient back-end for a program
which would export FORTRAN or C routines directly from the source code.
-----
Example 1 - cfortran.h has been used to make the C header file hbook.h,
which then gives any C programmer, e.g. example.c, full and
completely transparent access to CERN's HBOOK library of routines.
Each HBOOK routine required about 3 lines of simple code in
hbook.h. The example also demonstrates how FORTRAN common blocks
are defined and used.
/* hbook.h */
#include "cfortran.h"
:
PROTOCCALLSFSUB6(HBOOK1,hbook1,INT,STRING,INT,FLOAT,FLOAT,FLOAT)
#define HBOOK1(ID,CHTITLE,NX,XMI,XMA,VMX) \
CCALLSFSUB6(HBOOK1,hbook1,INT,STRING,INT,FLOAT,FLOAT,FLOAT, \
ID,CHTITLE,NX,XMI,XMA,VMX)
:
/* end hbook.h */
/* example.c */
#include "hbook.h"
:
typedef struct {
int lines;
int status[SIZE];
float p[SIZE]; /* momentum */
} FAKE_DEF;
#define FAKE COMMON_BLOCK(FAKE,fake)
COMMON_BLOCK_DEF(FAKE_DEF,FAKE);
:
main ()
{
:
HBOOK1(1,"pT spectrum of pi+",100,0.,5.,0.);
/* c.f. the call in FORTRAN:
CALL HBOOK1(1,'pT spectrum of pi+',100,0.,5.,0.)
*/
:
FAKE.p[7]=1.0;
:
}
N.B. i) The routine is language independent.
ii) hbook.h is machine independent.
iii) Applications using routines via cfortran.h are machine independent.
-----
Example 2 - Many VMS System calls are most easily called from FORTRAN, but
cfortran.h now gives that ease in C.
#include "cfortran.h"
PROTOCCALLSFSUB3(LIB$SPAWN,lib$spawn,STRING,STRING,STRING)
#define LIB$SPAWN(command,input_file,output_file) \
CCALLSFSUB3(LIB$SPAWN,lib$spawn,STRING,STRING,STRING, \
command,input_file,output_file)
main ()
{
LIB$SPAWN("set term/width=132","","");
}
Obviously the cfortran.h command above could be put into a header file along
with the description of the other system calls, but as this example shows, it's
not much hassle to set up cfortran.h for even a single call.
-----
Example 3 - cfortran.h and the source cstring.c create the cstring.obj library
which gives FORTRAN access to all the functions in C's system
library described by the system's C header file string.h.
C EXAMPLE.FOR
PROGRAM EXAMPLE
DIMENSION I(20), J(30)
:
CALL MEMCPY(I,J,7)
:
END
/* cstring.c */
#include <string.h> /* string.h prototypes memcpy() */
#include "cfortran.h"
:
FCALLSCSUB3(memcpy,MEMCPY,memcpy,PVOID,PVOID,INT)
:
The simplicity exhibited in the above example exists for many but not all
machines. Note 4. of Section II ii) details the limitations and describes tools
which try to maintain the best possible interface when FORTRAN calls C
routines.
-----
II Using cfortran.h
-------------------
The user is asked to look at the source files cfortest.c and cfortex.f
for clarification by example.
o) Notes:
o Specifying the Fortran compiler
cfortran.h generates interfaces for the default Fortran compiler. The default
can be overridden by defining,
. in the code, e.g.: #define NAGf90Fortran
OR . in the compile directive, e.g.: unix> cc -DNAGf90Fortran
one of the following before including cfortran.h:
NAGf90Fortran f2cFortran hpuxFortran apolloFortran sunFortran
IBMR2Fortran CRAYFortran mipsFortran DECFortran vmsFortran
CONVEXFortran PowerStationFortran AbsoftUNIXFortran
SXFortran pgiFortran AbsoftProFortran
This also allows crosscompilation.
If wanted, NAGf90Fortran, f2cFortran, DECFortran, AbsoftUNIXFortran,
AbsoftProFortran and pgiFortran must be requested by the user.
o /**/
cfortran.h (ab)uses the comment kludge /**/ when the ANSI C preprocessor
catenation operator ## doesn't exist. In at least MIPS C, this kludge is
sensitive to blanks surrounding arguments to macros.
Therefore, for applications using non-ANSI C compilers, the argtype_i,
routine_name, routine_type and common_block_name arguments to the
PROTOCCALLSFFUNn, CCALLSFSUB/FUNn, FCALLSCSUB/FUNn and COMMON_BLOCK macros
--- MUST NOT --- be followed by any white space characters such as
blanks, tabs or newlines.
o LOGICAL
FORTRAN LOGICAL values of .TRUE. and .FALSE. do not agree with the C
representation of TRUE and FALSE on all machines. cfortran.h does the
conversion for LOGICAL and PLOGICAL arguments and for functions returning
LOGICAL. Users must convert arrays of LOGICALs from C to FORTRAN with the
C2FLOGICALV(array_name, elements_in_array); macro. Similarly, arrays of LOGICAL
values may be converted from the FORTRAN into C representation by using
F2CLOGICALV(array_name, elements_in_array);
When C passes or returns LOGICAL values to FORTRAN, by default cfortran.h
only makes the minimal changes required to the value. [e.g. Set/Unset the
single relevant bit or do nothing for FORTRAN compilers which use 0 as FALSE
and treat all other values as TRUE.] Therefore cfortran.h will pass LOGICALs
to FORTRAN which do not have an identical representation to .TRUE. or .FALSE.
This is fine except for abuses of FORTRAN/77 in the style of:
logical l
if (l .eq. .TRUE.) ! (1)
instead of the correct:
if (l .eqv. .TRUE.) ! (2)
or:
if (l) ! (3)
For FORTRAN code which treats LOGICALs from C in the method of (1),
LOGICAL_STRICT must be defined before including cfortran.h, either in the
code, "#define LOGICAL_STRICT", or compile with "cc -DLOGICAL_STRICT".
There is no reason to use LOGICAL_STRICT for FORTRAN code which does not do (1).
At least the IBM's xlf and the Apollo's f77 do not even allow code along the
lines of (1).
DECstations' DECFortran and MIPS FORTRAN compilers use different internal
representations for LOGICAL values. [Both compilers are usually called f77,
although when both are installed on a single machine the MIPS' one is usually
renamed. (e.g. f772.1 for version 2.10.)] cc doesn't know which FORTRAN
compiler is present, so cfortran.h assumes MIPS f77. To use cc with DECFortran
define the preprocessor constant 'DECFortran'.
e.g. i) cc -DDECFortran -c the_code.c
or ii) #define DECFortran /* in the C code or add to cfortran.h. */
MIPS f77 [SGI and DECstations], f2c, and f77 on VAX Ultrix treat
.eqv./.neqv. as .eq./.ne.. Therefore, for these compilers, LOGICAL_STRICT is
defined by default in cfortran.h. [The Sun and HP compilers have not been
tested, so they may also require LOGICAL_STRICT as the default.]
o SHORT and BYTE
They are irrelevant for the CRAY where FORTRAN has no equivalent to C's short.
Similarly BYTE is irrelevant for f2c and for VAX Ultrix f77 and fort. The
author has tested SHORT and BYTE with a modified cfortest.c/cfortex.f on all
machines supported except for the HP9000 and the Sun.
BYTE is a signed 8-bit quantity, i.e. values are -128 to 127, on all machines
except for the SGI [at least for MIPS Computer Systems 2.0.] On the SGI it is
an unsigned 8-bit quantity, i.e. values are 0 to 255, although the SGI 'FORTRAN
77 Programmers Guide' claims BYTE is signed. Perhaps MIPS 2.0 is dated, since
the DECstations using MIPS 2.10 f77 have a signed BYTE.
To minimize the difficulties of signed and unsigned BYTE, cfortran.h creates
the type 'INTEGER_BYTE' to agree with FORTRAN's BYTE. Users may define
SIGNED_BYTE or UNSIGNED_BYTE, before including cfortran.h, to specify FORTRAN's
BYTE. If neither is defined, cfortran.h assumes SIGNED_BYTE.
o CRAY
The type DOUBLE in cfortran.h corresponds to FORTRAN's DOUBLE PRECISION.
The type FLOAT in cfortran.h corresponds to FORTRAN's REAL.
On a classic CRAY [i.e. all models except for the t3e]:
( 64 bit) C float == C double == Fortran REAL
(128 bit) C long double == Fortran DOUBLE PRECISION
Therefore when moving a mixed C and FORTRAN app. to/from a classic CRAY,
either the C code will have to change,
or the FORTRAN code and cfortran.h declarations will have to change.
DOUBLE_PRECISION is a cfortran.h macro which provides the former option,
i.e. the C code is automatically changed.
DOUBLE_PRECISION is 'long double' on classic CRAY and 'double' elsewhere.
DOUBLE_PRECISION thus corresponds to FORTRAN's DOUBLE PRECISION
on all machines, including classic CRAY.
On a classic CRAY with the fortran compiler flag '-dp':
Fortran DOUBLE PRECISION thus is also the faster 64bit type.
(This switch is often used since the application is usually satisfied by
64 bit precision and the application needs the speed.)
DOUBLE_PRECISION is thus not required in this case,
since the classic CRAY behaves like all other machines.
If DOUBLE_PRECISION is used nonetheless, then on the classic CRAY
the default cfortran.h behavior must be overridden,
for example by the C compiler option '-DDOUBLE_PRECISION=double'.
On a CRAY t3e:
(32 bit) C float == Fortran Unavailable
(64 bit) C double == C long double == Fortran REAL == Fortran DOUBLE PRECISION
Notes:
- (32 bit) is available as Fortran REAL*4 and
(64 bit) is available as Fortran REAL*8.
Since cfortran.h is all about more portability, not about less portability,
the use of the nonstandard REAL*4 and REAL*8 is strongly discouraged.
- Fortran DOUBLE PRECISION is folded to REAL with the following warning:
'DOUBLE PRECISION is not supported on this platform. REAL will be used.'
Similarly, Fortran REAL*16 is mapped to REAL*8 with a warning.
This behavior differs from that of other machines, including the classic CRAY.
FORTRAN_REAL is thus introduced for the t3e,
just as DOUBLE_PRECISION is introduced for the classic CRAY.
FORTRAN_REAL is 'double' on t3e and 'float' elsewhere.
FORTRAN_REAL thus corresponds to FORTRAN's REAL on all machines, including t3e.
o f2c / g77
f2c and g77 by default promote REAL functions to double. As of December 9,
2005, the Debian package of cfortran supports this behavior, so the f2c -R
option must *NOT* be used to turn this promotion off.
o f2c
[Thanks to Dario Autiero for pointing out the following.]
f2c has a strange feature in that either one or two underscores are appended
to a Fortran name of a routine or common block,
depending on whether or not the original name contains an underscore.
S.I. Feldman et al., "A fortran to C converter",
Computing Science Technical Report No. 149.
page 2, chapter 2: INTERLANGUAGE conventions
...........
To avoid conflict with the names of library routines and with names that
f2c generates,
Fortran names may have one or two underscores appended. Fortran names are
forced to lower case (unless the -U option described in Appendix B is in
effect); external names, i.e. the names of fortran procedures and common
blocks, have a single underscore appended if they do not contain any
underscore and have a pair of underscores appended if they do contain
underscores. Thus fortran subroutines names ABC, A_B_C and A_B_C_ result
in C functions named abc_, a_b_c__ and a_b_c___.
...........
cfortran.h is unable to change the naming convention on a name by name basis.
Fortran routine and common block names which do not contain an underscore
are unaffected by this feature.
Names which do contain an underscore may use the following work-around:
/* First 2 lines are a completely standard cfortran.h interface
to the Fortran routine E_ASY . */
PROTOCCALLSFSUB2(E_ASY,e_asy, PINT, INT)
#define E_ASY(A,B) CCALLSFSUB2(E_ASY,e_asy, PINT, INT, A, B)
#ifdef f2cFortran
#define e_asy_ e_asy__
#endif
/* Last three lines are a work-around for the strange f2c naming feature. */
o gfortran
gfortran behaves similarly to f2c and g77, EXCEPT that it does NOT by default
promote REAL functions to double. Therefore you should use -DgFortran instead
of -Dg77Fortran or -Df2cFortran to let cfortran.h know about this difference.
o NAG f90
The Fortran 77 subset of Fortran 90 is supported. Extending cfortran.h to
interface C with all of Fortran 90 has not yet been examined.
The NAG f90 library hijacks the main() of any program and starts the user's
program with a call to: void f90_main(void);
While this in itself is only a minor hassle, a major problem arises because
NAG f90 provides no mechanism to access command line arguments.
At least version 'NAGWare f90 compiler Version 1.1(334)' appended _CB to
common block names instead of the usual _. To fix, add this to cfortran.h:
#ifdef old_NAG_f90_CB_COMMON
#define COMMON_BLOCK CFC_ /* for all other Fortran compilers */
#else
#define COMMON_BLOCK(UN,LN) _(LN,_CB)
#endif
o RS/6000
Using "xlf -qextname ...", which appends an underscore, '_', to all FORTRAN
external references, requires "cc -Dextname ..." so that cfortran.h also
generates these underscores.
Use -Dextname=extname if extname is a symbol used in the C code.
The use of "xlf -qextname" is STRONGLY ENCOURAGED, since it allows for
transparent naming schemes when mixing C and Fortran.
o HP9000
Using "f77 +ppu ...", which appends an underscore, '_', to all FORTRAN
external references, requires "cc -Dextname ..." so that cfortran.h also
generates these underscores.
Use -Dextname=extname if extname is a symbol used in the C code.
The use of "f77 +ppu" is STRONGLY ENCOURAGED, since it allows for
transparent naming schemes when mixing C and Fortran.
At least one release of the HP /lib/cpp.ansi preprocessor is broken and will
go into an infinite loop when trying to process cfortran.h with the
## catenation operator. The K&R version of cfortran.h must then be used and the
K&R preprocessor must be specified. e.g.
HP9000> cc -Aa -tp,/lib/cpp -c source.c
The same problem with a similar solution exists on the Apollo.
An irrelevant error message '0: extraneous name /usr/include' will appear for
each source file due to another HP bug, and can be safely ignored.
e.g. 'cc -v -c -Aa -tp,/lib/cpp cfortest.c' will show that the driver passes
'-I /usr/include' instead of '-I/usr/include' to /lib/cpp
On some machines the above error causes compilation to stop; one must then use
K&R C, as with old HP compilers which don't support function prototyping.
cfortran.h has to be informed that K&R C is to being used, e.g.
HP9000> cc -D__CF__KnR -c source.c
o AbsoftUNIXFortran
By default, cfortran.h follows the default AbsoftUNIX/ProFortran and prepends _C
to each COMMON BLOCK name. To override the cfortran.h behavior
#define COMMON_BLOCK(UN,LN) before #including cfortran.h.
[Search for COMMON_BLOCK in cfortran.h for examples.]
o Apollo
On at least one release, 'C compiler 68K Rev6.8(168)', the default C
preprocessor, from cc -A xansi or cc -A ansi, enters an infinite loop when
using cfortran.h. This Apollo bug can be circumvented by using:
. cc -DANSI_C_preprocessor=0 to force use of /**/, instead of '##'.
AND . The pre-ANSI preprocessor, i.e. use cc -Yp,/usr/lib
The same problem with a similar solution exists on the HP.
o Sun
Old versions of cc(1), say <~1986, may require help for cfortran.h applications:
. #pragma may not be understood, hence cfortran.h and cfortest.c may require
sun> mv cfortran.h cftmp.h && grep -v "^#pragma" <cftmp.h >cfortran.h
sun> mv cfortest.c cftmp.c && grep -v "^#pragma" <cftmp.c >cfortest.c
. Old copies of math.h may not include the following from a newer math.h.
[For an ancient math.h on a 386 or sparc, get similar from a new math.h.]
#ifdef mc68000 /* 5 lines Copyright (c) 1988 by Sun Microsystems, Inc. */
#define FLOATFUNCTIONTYPE int
#define RETURNFLOAT(x) return (*(int *)(&(x)))
#define ASSIGNFLOAT(x,y) *(int *)(&x) = y
#endif
o CRAY, Sun, Apollo [pre 6.8 cc], VAX Ultrix and HP9000
Only FORTRAN routines with less than 15 arguments can be prototyped for C,
since these compilers don't allow more than 31 arguments to a C macro. This can
be overcome, [see Section IV], with access to any C compiler without this
limitation, e.g. gcc, on ANY machine.
o VAX Ultrix
vcc (1) with f77 is not supported. Although:
VAXUltrix> f77 -c cfortex.f
VAXUltrix> vcc -o cfortest cfortest.c cfortex.o -lI77 -lU77 -lF77 && cfortest
will link and run. However, the FORTRAN standard I/O is NOT merged with the
stdin and stdout of C, and instead uses the files fort.6 and fort.5. For vcc,
f77 can't drive the linking, as for gcc and cc, since vcc objects must be
linked using lk (1). f77 -v doesn't tell much, and without VAX Ultrix manuals,
the author can only wait for the info. required.
fort (1) is not supported. Without VAX Ultrix manuals the author cannot
convince vcc/gcc/cc and fort to generate names of routines and COMMON blocks
that match at the linker, lk (1). i.e. vcc/gcc/cc prepend a single underscore
to external references, e.g. NAME becomes _NAME, while fort does not modify the
references. So ... either fort has prepend an underscore to external
references, or vcc/gcc/cc have to generate unmodified names. man 1 fort
mentions JBL, is JBL the only way?
o VAX VMS C
The compiler 'easily' exhausts its table space and generates:
%CC-F-BUGCHECK, Compiler bug check during parser phase .
Submit an SPR with a problem description.
At line number 777 in DISK:[DIR]FILE.C;1.
where the line given, '777', includes a call across C and FORTRAN via
cfortran.h, usually with >7 arguments and/or very long argument expressions.
This SPR can be staved off, with the simple modification to cfortran.h, such
that the relevant CCALLSFSUBn (or CCALLSFFUNn or FCALLSCFUNn) is not
cascaded up to CCALLSFSUB14, and instead has its own copy of the contents of
CCALLSFSUB14. [If these instructions are not obvious after examining cfortran.h
please contact the author.]
[Thanks go to Mark Kyprianou (kyp@stsci.edu) for this solution.]
o Mips compilers
e.g. DECstations and SGI, require applications with a C main() and calls to
GETARG(3F), i.e. FORTRAN routines returning the command line arguments, to use
two macros as shown:
:
CF_DECLARE_GETARG; /* This must be external to all routines. */
:
main(int argc, char *argv[])
{
:
CF_SET_GETARG(argc,argv); /* This must precede any calls to GETARG(3F). */
:
}
The macros are null and benign on all other systems. Sun's GETARG(3F) also
doesn't work with a generic C main() and perhaps a workaround similar to the
Mips' one exists.
o Alpha/OSF
Using the DEC Fortran and the DEC C compilers of DEC OSF/1 [RT] V1.2 (Rev. 10),
Fortran, when called from C, has occasional trouble using a routine received as
a dummy argument.
e.g. In the following the Fortran routine 'e' will crash when it tries to use
the C routine 'c' or the Fortran routine 'f'.
The example works on other systems.
C FORTRAN /* C */
integer function f() #include <stdio.h>
f = 2 int f_();
return int e_(int (*u)());
end
int c(){ return 1;}
integer function e(u) int d (int (*u)()) { return u();}
integer u
external u main()
e=u() { /* Calls to d work. */
return printf("d (c ) returns %d.\n",d (c ));
end printf("d (f_) returns %d.\n",d (f_));
/* Calls to e_ crash. */
printf("e_(c ) returns %d.\n",e_(c ));
printf("e_(f_) returns %d.\n",e_(f_));
}
Solutions to the problem are welcomed!
A kludge which allows the above example to work correctly, requires an extra
argument to be given when calling the dummy argument function.
i.e. Replacing 'e=u()' by 'e=u(1)' allows the above example to work.
o The FORTRAN routines are called using macro expansions, therefore the usual
caveats for expressions in arguments apply. The expressions to the routines may
be evaluated more than once, leading to lower performance and in the worst case
bizarre bugs.
o For those who wish to use cfortran.h in large applications. [See Section IV.]
This release is intended to make it easy to get applications up and running.
This implies that applications are not as efficient as they could be:
- The current mechanism is inefficient if a single header file is used to
describe a large library of FORTRAN functions. Code for a static wrapper fn.
is generated in each piece of C source code for each FORTRAN function
specified with the CCALLSFFUNn statement, irrespective of whether or not the
function is ever called.
- Code for several static utility routines internal to cfortran.h is placed
into any source code which #includes cfortran.h. These routines should
probably be in a library.
i) Calling FORTRAN routines from C:
--------------------------------
The FORTRAN routines are defined by one of the following two instructions:
for a SUBROUTINE:
/* PROTOCCALLSFSUBn is optional for C, but mandatory for C++. */
PROTOCCALLSFSUBn(ROUTINE_NAME,routine_name,argtype_1,...,argtype_n)
#define Routine_name(argname_1,..,argname_n) \
CCALLSFSUBn(ROUTINE_NAME,routine_name,argtype_1,...,argtype_n, \
argname_1,..,argname_n)
for a FUNCTION:
PROTOCCALLSFFUNn(routine_type,ROUTINE_NAME,routine_name,argtype_1,...,argtype_n)
#define Routine_name(argname_1,..,argname_n) \
CCALLSFFUNn(ROUTINE_NAME,routine_name,argtype_1,...,argtype_n, \
argname_1,..,argname_n)
Where:
'n' = 0->14 [SUBROUTINE's ->27] (easily expanded in cfortran.h to > 14 [27]) is
the number of arguments to the routine.
Routine_name = C name of the routine (IN UPPER CASE LETTERS).[see 2.below]
ROUTINE_NAME = FORTRAN name of the routine (IN UPPER CASE LETTERS).
routine_name = FORTRAN name of the routine (IN lower case LETTERS).
routine_type = the type of argument returned by FORTRAN functions.
= BYTE, DOUBLE, FLOAT, INT, LOGICAL, LONG, SHORT, STRING, VOID.
[Instead of VOID one would usually use CCALLSFSUBn.
VOID forces a wrapper function to be used.]
argtype_i = the type of argument passed to the FORTRAN routine and must be
consistent in the definition and prototyping of the routine s.a.
= BYTE, DOUBLE, FLOAT, INT, LOGICAL, LONG, SHORT, STRING.
For vectors, i.e. 1 dim. arrays use
= BYTEV, DOUBLEV, FLOATV, INTV, LOGICALV, LONGV, SHORTV,
STRINGV, ZTRINGV.
For vectors of vectors, i.e. 2 dim. arrays use
= BYTEVV, DOUBLEVV, FLOATVV, INTVV, LOGICALVV, LONGVV, SHORTVV.
For n-dim. arrays, 1<=n<=7 [7 is the maximum in Fortran 77],
= BYTEV..nV's..V, DOUBLEV..V, FLOATV..V, INTV..V, LOGICALV..V,
LONGV..V, SHORTV..V.
N.B. Array dimensions and types are checked by the C compiler.
For routines changing the values of an argument, the keyword is
prepended by a 'P'.
= PBYTE, PDOUBLE, PFLOAT, PINT, PLOGICAL, PLONG, PSHORT,
PSTRING, PSTRINGV, PZTRINGV.
For EXTERNAL procedures passed as arguments use
= ROUTINE.
For exceptional arguments which require no massaging to fit the
argument passing mechanisms use
= PVOID.
The argument is cast and passed as (void *).
Although PVOID could be used to describe all array arguments on
most (all?) machines , it shouldn't be because the C compiler
can no longer check the type and dimension of the array.
argname_i = any valid unique C tag, but must be consistent in the definition
as shown.
Notes:
1. cfortran.h may be expanded to handle a more argument type. To suppport new
arguments requiring complicated massaging when passed between Fortran and C,
the user will have to understand cfortran.h and follow its code and mechanisms.
To define types requiring little or no massaging when passed between Fortran
and C, the pseudo argument type SIMPLE may be used.
For a user defined type called 'newtype', the definitions required are:
/* The following 7 lines are required verbatim.
'newtype' is the name of the new user defined argument type.
*/
#define newtype_cfV( T,A,B,F) SIMPLE_cfV(T,A,B,F)
#define newtype_cfSEP(T, B) SIMPLE_cfSEP(T,B)
#define newtype_cfINT(N,A,B,X,Y,Z) SIMPLE_cfINT(N,A,B,X,Y,Z)
#define newtype_cfSTR(N,T,A,B,C,D,E) SIMPLE_cfSTR(N,T,A,B,C,D,E)
#define newtype_cfCC( T,A,B) SIMPLE_cfCC(T,A,B)
#define newtype_cfAA( T,A,B) newtype_cfB(T,A) /* Argument B not used. */
#define newtype_cfU( T,A) newtype_cfN(T,A)
/* 'parameter_type(A)' is a declaration for 'A' and describes the type of the
parameter expected by the Fortran function. This type will be used in the
prototype for the function, if using ANSI C, and to declare the argument used
by the intermediate function if calling a Fortran FUNCTION.
Valid 'parameter_type(A)' include: int A
void (*A)()
double A[17]
*/
#define newtype_cfN( T,A) parameter_type(A) /* Argument T not used. */
/* Before any argument of the new type is passed to the Fortran routine, it may
be massaged as given by 'massage(A)'.
*/
#define newtype_cfB( T,A) massage(A) /* Argument T not used. */
An example of a simple user defined type is given cfortex.f and cfortest.c.
Two uses of SIMPLE user defined types are [don't show the 7 verbatim #defines]:
/* Pass the address of a structure, using a type called PSTRUCT */
#define PSTRUCT_cfN( T,A) void *A
#define PSTRUCT_cfB( T,A) (void *) &(A)
/* Pass an integer by value, (not standard F77 ), using a type called INTVAL */
#define INTVAL_cfN( T,A) int A
#define INTVAL_cfB( T,A) (A)
[If using VAX VMS, surrounding the #defines with "#pragma (no)standard" allows
the %CC-I-PARAMNOTUSED messages to be avoided.]
Upgrades to cfortran.h try to be, and have been, backwards compatible. This
compatibility cannot be offered to user defined types. SIMPLE user defined
types are less of a risk since they require so little effort in their creation.
If a user defined type is required in more than one C header file of interfaces
to libraries of Fortran routines, good programming practice, and ease of code
maintenance, suggests keeping any user defined type within a single file which
is #included as required. To date, changes to the SIMPLE macros were introduced
in versions 2.6, 3.0 and 3.2 of cfortran.h.
2. Routine_name is the name of the macro which the C programmer will use in
order to call a FORTRAN routine. In theory Routine_name could be any valid and
unique name, but in practice, the name of the FORTRAN routine in UPPER CASE
works everywhere and would seem to be an obvious choice.
3. <BYTE|DOUBLE|FLOAT|INT|LOGICAL|LONG|SHORT><V|VV|VVV|...>
cfortran.h encourages the exact specification of the type and dimension of
array parameters because it allows the C compiler to detect errors in the
arguments when calling the routine.
cfortran.h does not strictly require the exact specification since the argument
is merely the address of the array and is passed on to the calling routine.
Any array parameter could be declared as PVOID, but this circumvents
C's compiletime ability to check the correctness of arguments and is therefore
discouraged.
Passing the address of these arguments implies that PBYTEV, PFLOATV, ... ,
PDOUBLEVV, ... don't exist in cfortran.h, since by default the routine and the
calling code share the same array, i.e. the same values at the same memory
location.
These comments do NOT apply to arrays of (P)S/ZTRINGV. For these parameters,
cfortran.h passes a massaged copy of the array to the routine. When the routine
returns, S/ZTRINGV ignores the copy, while PS/ZTRINGV replaces the calling
code's original array with copy, which may have been modified by the called
routine.
4. (P)STRING(V):
- STRING - If the argument is a fixed length character array, e.g. char ar[8];,
the string is blank, ' ', padded on the right to fill out the array before
being passed to the FORTRAN routine. The useful size of the string is the same
in both languages, e.g. ar[8] is passed as character*7. If the argument is a
pointer, the string cannot be blank padded, so the length is passed as
strlen(argument). On return from the FORTRAN routine, pointer arguments are not
disturbed, but arrays have the terminating '\0' replaced to its original
position. i.e. The padding blanks are never visible to the C code.
- PSTRING - The argument is massaged as with STRING before being passed to the
FORTRAN routine. On return, the argument has all trailing blanks removed,
regardless of whether the argument was a pointer or an array.
- (P)STRINGV - Passes a 1- or 2-dimensional char array. e.g. char a[7],b[6][8];
STRINGV may thus also pass a string constant, e.g. "hiho".
(P)STRINGV does NOT pass a pointer, e.g. char *, to either a 1- or a
2-dimensional array, since it cannot determine the array dimensions.
A pointer can only be passed using (P)ZTRINGV.
N.B. If a C routine receives a character array argument, e.g. char a[2][3],
such an argument is actually a pointer and my thus not be passed by
(P)STRINGV. Instead (P)ZTRINGV must be used.
- STRINGV - The elements of the argument are copied into space malloc'd, and
each element is padded with blanks. The useful size of each element is the same
in both languages. Therefore char bb[6][8]; is equivalent to character*7 bb(6).
On return from the routine the malloc'd space is simply released.
- PSTRINGV - Since FORTRAN has no trailing '\0', elements in an array of
strings are contiguous. Therefore each element of the C array is padded with
blanks and strip out C's trailing '\0'. After returning from the routine, the
trailing '\0' is reinserted and kill the trailing blanks in each element.
- SUMMARY: STRING(V) arguments are blank padded during the call to the FORTRAN
routine, but remain original in the C code. (P)STRINGV arguments are blank
padded for the FORTRAN call, and after returning from FORTRAN trailing blanks
are stripped off.
5. (P)ZTRINGV:
- (P)ZTRINGV - is identical to (P)STRINGV,
except that the dimensions of the array of strings is explicitly specified,
which thus also allows a pointer to be passed.
(P)ZTRINGV can thus pass a 1- or 2-dimensional char array, e.g. char b[6][8],
or it can pass a pointer to such an array, e.g. char *p;.
ZTRINGV may thus also pass a string constant, e.g. "hiho".
If passing a 1-dimensional array, routine_name_ELEMS_j (see below) must be 1.
[Users of (P)ZTRINGV should examine cfortest.c for examples.]:
- (P)ZTRINGV must thus be used instead of (P)STRINGV whenever sizeof()
can't be used to determine the dimensions of the array of string or strings.
e.g. when calling FORTRAN from C with a char * received by C as an argument.
- There is no (P)ZTRING type, since (P)ZTRINGV can pass a 1-dimensional
array or a pointer to such an array, e.g. char a[7], *b;
If passing a 1-dimensional array, routine_name_ELEMS_j (see below) must be 1.
- To specify the numbers of elements,
routine_name_ELEMS_j and routine_name_ELEMLEN_j must be defined as shown below
before interfacing the routine with CCALLSFSUBn, PROTOCCALLSFFUNn, etc.
#define routine_name_ELEMS_j ZTRINGV_ARGS(k)
[..ARGS for subroutines, ..ARGF for functions.]
or
#define routine_name_ELEMS_j ZTRINGV_NUM(l)
Where: routine_name is as above.
j [1-n], is the argument being specifying.
k [1-n], the value of the k'th argument is the dynamic number
of elements for argument j. The k'th argument must be
of type BYTE, DOUBLE, FLOAT, INT, LONG or SHORT.
l the number of elements for argument j. This must be an
integer constant available at compile time.
i.e. it is static.
- Similarly to specify the useful length, [i.e. don't count C's trailing '\0',]
of each element:
#define routine_name_ELEMLEN_j ZTRINGV_ARGS(m)
[..ARGS for subroutines, ..ARGF for functions.]
or
#define routine_name_ELEMLEN_j ZTRINGV_NUM(q)
Where: m [1-n], as for k but this is the length of each element.
q as for l but this is the length of each element.
6. ROUTINE
The argument is an EXTERNAL procedure.
When C passes a routine to Fortran, the language of the function must be
specified as follows: [The case of some_*_function must be given as shown.]
When C passes a C routine to a Fortran:
FORTRAN_ROUTINE(arg1, .... ,
C_FUNCTION(SOME_C_FUNCTION,some_c_function),
...., argn);