Handling Integer Pointers

Integer pointers (also known as Cray*-style pointers) are not the same as Fortran 90 pointers, but are instead like C pointers. Integer pointers are 4-byte INTEGER quantities on IA-32 systems, and 8-byte INTEGER quantities on Intel®EM64T and Itanium®-based systems.

Passing Integer Pointers

When passing an integer pointer to a routine written in another language:

• The argument should be declared in the non-Fortran routine as a pointer of the appropriate data type.

• The argument passed from the Fortran routine should be the integer pointer name, not the pointee name.

For example:

! Fortran main program.
INTERFACE
  SUBROUTINE Ptr_Sub (p)
 !DEC$ ATTRIBUTES C, ALIAS:'Ptr_Sub' :: Ptr_Sub
     INTEGER (KIND=INT_PTR_KIND()) p
  END SUBROUTINE Ptr_Sub
END INTERFACE
REAL A(10), VAR(10)
POINTER (p, VAR) ! VAR is the pointee
                ! p is the integer pointer
p = LOC(A)
CALL Ptr_Sub (p)
WRITE(*,*) 'A(4) = ', A(4)
END
!
//C subprogram
void Ptr_Sub (float *p)
{
 p[3] = 23.5;
}

On Intel® EM64T and Itanium-based systems, the declaration for p in the INTERFACE block is equivalent to INTEGER(8) p and on IA-32 systems, it is equivalent to INTEGER (4) p.

When the main Fortran program and C function are built and executed, the following output appears:

A(4) = 23.50000

Receiving Pointers

When receiving a pointer from a routine written in another language:

• The argument should be declared in the non-Fortran routine as a pointer of the appropriate data type and passed as usual.

• The argument received by the Fortran routine should be declared as an integer pointer name, and the POINTER statement should associate it with a pointee of the appropriate data type (matching the data type of the passing routine). When inside the Fortran routine, use the pointee to set and access what the pointer points to. The pointer must be passed by value.

For example:

! Fortran subroutine.
SUBROUTINE Iptr_Sub (p)
!DEC$ ATTRIBUTES C, ALIAS:'Iptr_Sub' :: Iptr_Sub
  integer VAR(10)
  POINTER (p, VAR)
  OPEN (8, FILE='STAT.DAT')
  READ (8, *) VAR(4) ! Read from file and store the
                     ! fourth element of VAR      
END SUBROUTINE Iptr_Sub
!
//C main program
extern void Iptr_Sub(int *p);
main ( void ) {   int a[10];
Iptr_Sub (&a[0]);
printf("a[3] = %i\n", a[3]);
}

When the main C program and Fortran subroutine are built and executed, the following output appears if the STAT.DAT file contains 4:

   a[3] = 4