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Sun Studio 12: Fortran Programming Guide

11.3.6 Structures

C and Fortran 95 derived types can be passed to each other’s routines as long as the corresponding elements are compatible.( f95 accepts legacy STRUCTURE statements.)

Table 11–8 Passing Legacy FORTRAN 77 STRUCTURE Records

Fortran calls C  

C calls Fortran  

 

STRUCTURE /POINT/
REAL X, Y, Z
END STRUCTURE
RECORD /POINT/ BASE
EXTERNAL FLIP
...
CALL FLIP( BASE )
...

------------------------------

struct point {
    float x,y,z;
};
void flip_( struct point *v )
{
    float t;
    t = v -> x;
    v -> x = v -> y;
    v -> y = t;
    v -> z = -2.*(v -> z);
}


struct point {
    float x,y,z;
};
void fflip_ ( struct point *) ;
...
struct point d;
struct point *ptx = &d;
...
fflip_ (ptx);
...

------------------------------

SUBROUTINE FFLIP(P)
  STRUCTURE /POINT/
    REAL X,Y,Z
  END STRUCTURE
  RECORD /POINT/ P
  REAL T
  T = P.X
  P.X = P.Y
  P.Y = T
  P.Z = -2.*P.Z
  ...

Note that Fortran 77 (VAX) structures always have the same alignment as C structures on all platforms. However, the alignment changes between platforms.

Table 11–9 Passing Fortran 95 Derived Types

Fortran 95 calls C  

C calls Fortran 95  

 

TYPE point
  SEQUENCE
  REAL :: x, y, z
END TYPE point
TYPE (point) base
EXTERNAL flip
...
CALL flip( base)
...

------------------------------

struct point {
    float x,y,z;
};
void flip_( struct point *v )
{<
    float t;
    t = v -> x;
    v -> x = v -> y;
    v -> y = t;
    v -> z = -2.*(v -> z);
}


struct point {
  float x,y,z;
};
extern void fflip_ (
     struct point *) ;
...
struct point d;
struct point *ptx = &d;
...
fflip_ (ptx);
...

------------------------------

SUBROUTINE FFLIP( P )
    TYPE POINT
     SEQUENCE
     REAL :: X, Y, Z
    END TYPE POINT
    TYPE (POINT) P
    REAL :: T
    T = P%X
    P%X = P%Y
    P%Y = T
    P%Z = -2.*P%Z
    ...

Note that the Fortran 95 standard requires the SEQUENCE statement in the definition of the derived type to insure that storage sequence order be preserved by the compiler.

The components of a numeric sequence type are aligned on word (4-byte) boundaries on all platforms by default. This matches the alignment of C structures on x86 platforms, but differs from the alignment of C structures on SPARC platforms. Use the -aligncommon option to change the alignment of numeric sequence types to match C structures. Use -aligncommon=8 to match 32–bit SPARC C structures, -aligncommon=16 to match 64–bit SPARC.

Derived types not explicitly declared with SEQUENCE have the same alignment as C structures on SPARC platforms, but differ on x86 platforms. This alignment cannot be changed with a compiler option.