CODEWITHSUNDEEP
pointersfortran
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Reputation: 417

One pointer for different types Fortran

I'am trying to write a procedure, which store addresses of user arrays for further processing. Problem is encapsulated in this test program:

program test_ptr
    real(4), target, allocatable :: i4(:,:)
    real(8), target, allocatable :: i8(:,:)
    real(4), pointer :: p(:,:)

    allocate(i4(2,2))
    allocate(i8(2,2))

    p => i4 ! ok
    p => i8 ! compile error
end

The compiler suggests making different pointers for different types. But I don't want to create separate pointers for real(4) and real(8). I'am trying to make generic and compact solution and have one pointer for different types of data. Is it possible?

Upvotes: 1

Views: 638

Answers (2)

Vladimir F Героям слава
Vladimir F Героям слава

Reputation: 60008

If you really want to store adresses I would be careful with polymorphism. Pointers to polymorphic variables often point to a descriptor which has different address than the real data. Consider using type(c_ptr) defined in the iso_c_binding module and the function c_loc() to obtain the address. It doesn't have to be used only for interfacing to C, there are couple of places where it is handy in pure Fortran.

Upvotes: 2

francescalus
francescalus

Reputation: 32366

It is possible to do this using (unlimited) polymorphism for p.

program test_ptr
  implicit none

  real(kind(0.)), target :: r4(2,2)
  real(kind(0d0)), target :: r8(2,2)

  class(*), pointer :: p(:,:)

  ! some assignments, etc.

  if (...some crazy condition...) then
    p => r4
  else
    p => r8
  end if

  select type (p)
    type is (real(kind(0.)))
      print *, p
    type is (real(kind(0d0)))
      print *, p
  end select

end program

Pay particular attention to the select type for when later using p.

Upvotes: 5

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