Handling Compaq Fortran Pointers

Compaq Fortran (integer) pointers are not the same as Fortran 90 pointers, but are instead like C pointers. On ia32 systems, Compaq Fortran pointers are 4-byte INTEGER quantities. On ia64 systems, Compaq Fortran pointers are 8-byte INTEGER quantities.

When passing a Compaq Fortran 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 Compaq Fortran pointer name, not the pointer-based variable name.
  For example, on ia32 systems:

   ! Fortran main program.
        INTERFACE
           SUBROUTINE Ptr_Sub (p)
           !DEC$ ATTRIBUTES C, ALIAS:'_Ptr_Sub' :: Ptr_Sub
              INTEGER p
           END SUBROUTINE Ptr_Sub
        END INTERFACE
        REAL A(10), VAR(10)
        POINTER (p, VAR) ! VAR is the pointer-based
                         ! variable, p is the int.
        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 ia64 systems, the alias name for Ptr_Sub should not have a leading underscore, as follows:

     !DEC$ ATTRIBUTES C, ALIAS:'Ptr_Sub' :: Ptr_Sub
  

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

     A(4) = 23.50000
  

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 a Compaq Fortran pointer name, then the POINTER statement should associate it with a pointer-based variable of the appropriate data type (matching the data type of the passing routine). When inside the Fortran routine, use the pointer-based variable to set and access what the pointer points to.

For example, on ia32 systems:

 ! 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]);
 }

   !DEC$ ATTRIBUTES C, ALIAS:'Iptr_Sub' :: Iptr_Sub

   a[3] = 4