Mix Fortran77 & C - Collected Slides

Slide 1

1 Title Page

Mix Fortran77 & C - Title Page

Mix Fortran77 & C

R.K. Owen,Ph.D.
KooZ Software

email:rk@owen.sj.ca.us
email:rkowen@nersc.gov

Slide 2

2 Fortran & C

Mix Fortran77 & C - Fortran & C

Fortran :
- Passes by address
- Routine names are case insensitive
- Arrays are column-major
- Strings contain length
C :
- Passes by value
- Names are case sensitive
- Arrays are row-major
- "Strings" are null terminated

Slide 3

2.1 IBM SP2

Mix Fortran77 & C - IBM SP2 F77 & C

Fortran	C	size(bits)
`INTEGER*1`	`signed char`	8
`INTEGER*2`	`short`	16
`INTEGER`	`int`	32
`REAL`	`float`	32
`DOUBLE PRECISION`	`double`	64
`COMPLEX`	2 `float struct`	64
`DOUBLE COMPLEX`	2 `double struct`	128
`SUBROUTINE SUBR( )`	`void subr( )`
`FUNCTION FN( )`	`float fn( )`
`COMMON /CB/data(10)`	?

Slide 4

2.2 CRI C90

Mix Fortran77 & C - Cray F77 & C

Fortran	C	size(bits)
`INTEGER`	`int`	46/64
cft77 -i64	cc -nofastmd
`INTEGER`	`long`	64
`REAL`	`double` or `float`	64
`DOUBLE PRECISION`	`long double`	128
`COMPLEX`	`float complex` or `double complex`	128
`SUBROUTINE SUBR( )`	`void SUBR( )`
`FUNCTION FN( )`	`double FN( )`
`COMMON /CB/data(10)`	`struct common {` `double data[10];` `} CB;`

Slide 5

2.2

Mix Fortran77 & C - F77 & C - more

Note Differences

Cray Y-MP/J90/C90
- Fortran names are UPPERCASE
- C preprocess defines _CRAY
- Special C header to handle Fortran strings
IBM SP2
- Fortran names are lowercase
- C preprocess defines _AIX
- Common blocks from C (?)
- No problem passing strings
Typical Workstation
- Fortran names are generally lowercase and `_' is appended
- Usually no problem passing strings

Slide 6

2.3 Fortran to C

Mix Fortran77 & C - F77 & C example

Fortran calling C function

Fortran Main

 
      PROGRAM F2C
C
      CHARACTER*32 NAME
      INTEGER AGE
      REAL TEMP
C
      NAME = "Knut"
C add null character at end for portable & safe handling by C
      NAME(LEN(NAME):LEN(NAME)) = CHAR(0)
C note that LEN(NAME) = 32 in this case
      AGE = 4
      TEMP = 98.6
      CALL NAMEAGE(NAME, AGE, TEMP)
      END

C Function

 
#include <string.h>
#ifdef _CRAY
#  include <fortran.h>
#  define nameage       NAMEAGE
#else
#  ifndef _AIX
#    define nameage	nameage_
#  endif
#  define _fcd          char *
#  define _fcdtocp(a)   (a)
#  define _fcdlen(a)    strlen(a)
#endif

void nameage(_fcd name, int *age, float *temp) {
        char *cp;
        size_t len;

        cp = _fcdtocp(name);    /* convert to C char* */
        len = _fcdlen(name);

        /* strip trailing blanks */
        while (cp[len-1] == ' ' || cp[len-1] == '\0') --len;
        printf("Hello %.*s, who is %d years old, "
                "has a temperature of %4.1f\n", len, cp, *age, *temp);
}

Compilation Steps

Cray - PVPs - UNICOS
- cc -c f2cfn.c
- cf77 f2c.f f2cfn.o
- (or substitute f90 for cf77)
IBM - SP2 - AIX
- xlc -c f2cfn.c
- xlf f2c.f f2cfn.o
SGI - IRIX
- gcc -c f2cfn.c
- f77 f2c.f f2cfn.o
SUN - SunOS
- gcc -c f2cfn.c
- f77 f2c.f f2cfn.o
PC - Linux
- gcc -c f2cfn.c
- g77 f2c.f f2cfn.o

Slide 7

2.4 C to Fortran

Mix Fortran77 & C - F77 & C example

C calling Fortran subroutine

C Main

 
#include <string.h>
#ifdef _CRAY
#  include <fortran.h>
#  define nameage      NAMEAGE
#else
#  ifndef _AIX
#    define nameage    nameage_
#  endif
#  define _fcd          char *
#  define _cptofcd(a,b) (a)
#  define _fcdlen(a)    strlen(a)
#endif

void nameage(_fcd name, int *nlen, int *age, float *temp);

int main() {
        char *name = "Knut";
        _fcd fp;
        int nlen,age = 4;
        float temp = 98.6;

        nlen = strlen(name);
        fp = _cptofcd(name, nlen);      /* convert to Fortran string */

        nameage(fp, &nlen, &age, &temp);
        return 0;
}

Fortran Subroutine

 
      SUBROUTINE NAMEAGE(NAME, NLEN, AGE, TEMP)
      CHARACTER*(*) NAME
      INTEGER NLEN,AGE
      REAL TEMP
C
      WRITE(6,1000) NAME(1:NLEN),AGE,TEMP
 1000 FORMAT(1X,'Hello ',A,', who is ',I2,
     .      ' years old, has a temperature of ', f4.1)
      RETURN
      END

Compilation Steps

To discover which libraries are necessary for Fortran modules, compile a short Fortran test program and add the -V option (or equivalent) to get a verbose execution listing.

Cray - PVPs - UNICOS
- cf77 -c c2ffn.f
- cc -c c2f.c
- cf77 c2f.o c2ffn.o
- (or substitute f90 for cf77)
IBM - SP2 - AIX
- xlf -c c2ffn.f
- cc c2f.c c2ffn.o -lxlf90 -lxlf -lm
SGI - IRIX
- f77 -c c2ffn.f
- gcc c2f.c c2ffn.o -lF77 -lm -lU77 -lI77 -lisam -lmpc -lc
SUN - SunOS
- f77 -c c2ffn.f
- gcc c2f.c c2ffn.o -L/usr/lang/SC0.0 -lF77 -lm -lc
PC - Linux
- g77 -c c2ffn.f
- gcc -c c2f.c
- g77 c2f.o c2ffn.o

Last Modified:

Brought to you by: R.K. Owen, Ph.D.
This page is http://rkowen.owentrek.com/howto/slides/FandC/ALL.html