Mix Fortran77 & C - Collected Slides

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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

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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

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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)	?

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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;

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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

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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

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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