simple pointer problem

[ya0037]

Dears,

I have a strange problem which I do not understand what is it.
Based on pointers definition the simple code which I wrote below should work, but it does not please help me.

module all
contains
subroutine deall(a)
  integer, pointer :: a
  integer, pointer :: curr => null()
  curr => a
  if (associated(curr)) then
     deallocate(curr)
     nullify(curr)
  endif
end subroutine deall
end module

program test
  use all
  implicit none
  integer, pointer :: a=>null()
  integer, pointer :: b=>null()
  allocate(a)
  a=10
  print*,associated(a)
  call deall(a)
  print*,associated(a)
End Program test

the subroutine can not deallocate the pointer which according to text book should be the case
please help me in this regard.

cheers,

 

[xwb]

You've got what is known in Computer Science as a dangling reference. Basically whatever a was pointing to has been deallocated but a doesn't know about it. That is why languages like C# and Java have introduced reference counting: it is to avoid such problems (but you're not out of the woods - there are other problems)

subroutine deall(curr)
  integer, pointer :: curr
  integer, pointer :: dangling
  dangling => curr
  if (associated(curr)) then
     deallocate(curr)
     nullify(curr)
  endif
  print *, 'current  is ', associated(curr)
  print *, 'dangling is ', associated(dangling)
end subroutine deall