passing pointer component of derived type into subroutine

[narlytep]

Hi.
One of our users is having a problem and I'm a bit stumped as well. They're trying to pass a pointer component of a derived type into a subroutine and treating it as a normal array at the other end. However the data is ending up as garbage.

Is this legal?

module mod
type deriv
integer :: dummy
real(kind=8), dimension), pointer :: p
end type deriv
type(deriv) :: struct
end module mod

subroutine sub1()
use mod
implicit none

interface
subroutine sub2(t)
real(kind=8), dimension(0:25), intent(in) :: t
end subroutine sub2
end interface

allocate(struct%p(0:25))
! Set values of struct%p here........
!
call sub2(struct%p)
end subroutine sub1

subroutine sub2(t)
real(kind=8), dimension(0:25), intent(in) :: t
print*, t(0), t(1), t(2)
end subroutine sub2

-----------------------------------
Although struct%p contains the value 5.0 throughout (apart from index 0 which holds 0.0), the t array in sub2 holds:

3.2e-324 <denormalised>
3.2e-324 <denormalised>
0
3.2e-324 <denormalised>
3.2e-324 <denormalised>
0
etc.

The memory address for struct%p and t are identical.

Any help appreciated!

 

[xwb]

It shouldn't be a pointer. Try these mods

module mod
  type deriv
     integer :: dummy
[COLOR=red]     real(kind=8), dimension(:) :: p[/color]
  end type deriv
  type(deriv) :: struct
end module mod

subroutine sub1()
  use mod
  implicit none

  interface
    subroutine sub2(t)
[COLOR=red]      real(kind=8), dimension(:), intent(in) :: t[/color]
    end subroutine sub2
  end interface

  allocate(struct%p(0:25))
! Set values of struct%p here........
!
  call sub2(struct%p)
end subroutine sub1

subroutine sub2(t)
[COLOR=red]  real(kind=8), dimension(:), intent(in) :: t[/color]
  print*, t(0), t(1), t(2)
end subroutine sub2

 

[zhouxian]

could you explain more about the difference in using pointer and array in fortran?