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dongli
Joined: 26 May 2009
Posts: 2
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 Posted: Sun Nov 11, 2012 12:30 am Post subject: Double linked list problem (type is not judged correctly) |
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Dear all,
I would like to implement a generic double linked list in Fortran for saving codes. Here is my prototype, including 3 files:
--------------------------- File 1 ---------------------------
| Code: |
! ----------------------------------------------------------------------------
! Description:
!
! This module provides several basic data structures, e.g. double linked list.
!
! Authors:
!
! Li Dong <dongli@lasg.iap.ac.cn> - 2012-11-11
! ----------------------------------------------------------------------------
module basic_data_structure
implicit none
private
public list_elem_t, list_t
type list_elem_t
class(list_elem_t), pointer :: prev, next
end type list_elem_t
type list_t
integer :: num_elem = 0
class(list_elem_t), pointer :: head, tail
contains
procedure :: append => list_append
procedure :: insert => list_insert
procedure :: final => list_final
end type list_t
contains
! ------------------------------------------------------------------------
! Description:
!
! The following list_* are the type-bound procedures of double linked
! list data structure.
!
! Authors:
!
! Li Dong - <dongli@lasg.iap.ac.cn> - 2012-11-11
! ------------------------------------------------------------------------
subroutine list_append(this, elem)
class(list_t), intent(inout) :: this
class(list_elem_t), intent(out), pointer :: elem
character(50), parameter :: sub_name = "list_append"
allocate(elem)
if (this%num_elem == 0) then
this%head => elem
nullify(this%head%prev)
this%tail => this%head
else
this%tail%next => elem
elem%prev => this%tail
this%tail => elem
end if
nullify(this%tail%next)
this%num_elem = this%num_elem+1
end subroutine list_append
subroutine list_insert(this, existed_elem, elem)
class(list_t), intent(inout) :: this
class(list_elem_t), intent(inout), pointer :: existed_elem
class(list_elem_t), intent(out), pointer :: elem
character(50), parameter :: sub_name = "list_insert"
! TODO: Check existed_elem is allocated.
! TODO: Check existed_elem is one element of this.
allocate(elem)
elem%prev => existed_elem
elem%next => existed_elem%next
if (associated(existed_elem%next)) then
existed_elem%next%prev => elem
existed_elem%next => elem
end if
this%num_elem = this%num_elem+1
end subroutine list_insert
subroutine list_final(this)
class(list_t), intent(inout) :: this
class(list_elem_t), pointer :: elem
integer i
elem => this%head
do i = 1, this%num_elem-1
elem => elem%next
if (associated(elem%prev)) deallocate(elem%prev)
end do
deallocate(this%tail)
end subroutine list_final
end module basic_data_structure
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--------------------------- File 2 ---------------------------
| Code: |
! ----------------------------------------------------------------------------
! Description:
!
! This module manages the model variables.
!
! Authors:
!
! Li Dong <dongli@lasg.iap.ac.cn> - 2012-11-11
! ----------------------------------------------------------------------------
module variable
use basic_data_structure
implicit none
private
public variable_register
public variable_final
public var_t, var_1d_t
integer, parameter :: A_GRID = 1
integer, parameter :: B_GRID = 2
integer, parameter :: C_GRID = 3
type, extends(list_elem_t) :: var_t
character(10) name
character(50) long_name
character(20) units
integer grid_type
end type var_t
type, extends(var_t) :: var_1d_t
real(8), allocatable :: array(:)
end type var_1d_t
type, extends(var_t) :: var_2d_t
real(8), allocatable :: array(:,:)
end type var_2d_t
type(list_t) var_list
contains
! ------------------------------------------------------------------------
! Description:
!
! Register a variable.
!
! Authors:
!
! Li Dong <dongli@lasg.iap.ac.cn> - 2012-11-11
! ------------------------------------------------------------------------
subroutine variable_register(name, var)
character(*), intent(in) :: name
class(var_t), intent(inout), pointer :: var
character(50), parameter :: sub_name = "variable_register"
select type (var)
type is (var_1d_t)
print *, "---> Register a 1D variable """//trim(name)//"""."
type is (var_2d_t)
print *, "---> Register a 2D variable """//trim(name)//"""."
type is (var_t)
print *, "---> Oh, no!"
class default
print *, "---> Unknown variable type """//trim(name)//"""."
end select
call var_list%append(var)
! -------------------------------> PROBLEM IS HERE
select type (var)
type is (var_1d_t)
print *, "---> Register a 1D variable """//trim(name)//"""."
type is (var_2d_t)
print *, "---> Register a 2D variable """//trim(name)//"""."
type is (var_t)
print *, "---> Oh, no!"
class default
print *, "---> Unknown variable type """//trim(name)//"""."
end select
end subroutine variable_register
! ------------------------------------------------------------------------
! Description:
!
! Clean the registered variables.
!
! Authors:
!
! Li Dong <dongli@lasg.iap.ac.cn> - 2012-11-11
! ------------------------------------------------------------------------
subroutine variable_final()
character(50), parameter :: sub_name = "variable_final"
call var_list%final()
end subroutine variable_final
end module variable
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--------------------------- File 3 ---------------------------
| Code: |
program test_variable
use variable
implicit none
type(var_1d_t), pointer :: a
call variable_register("a", a)
call variable_final()
end program test_variable
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The running result is:
| Code: |
MacBook-Pro:sandbox dongli$ ./test_variable
---> Register a 1D variable "a".
---> Unknown variable type "a".
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Why after appending a list, the type of "var" is changed into a type that is unknown?
Any help is appreciated!
Li |
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dongli
Joined: 26 May 2009
Posts: 2
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| Posted: Sun Nov 11, 2012 6:22 pm Post subject: |
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| I think the problem is the allocate(elem), where elem is declared as a class(list_elem_t), pointer. Fortran loses the memory that elem is a type of type(var_1d_t). So we can not make list manage the memory, but the user. |
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mleair
Joined: 19 Jul 2004
Posts: 67
Location: Portland Group
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| Posted: Thu Nov 15, 2012 11:16 am Post subject: RE: doubly linked list |
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Hi Dongli,
Your allocate statement in list_append() creates an instance of list_elem_t not var_1d_t. By definition, an allocate statement will default to the declared type unless you use F2003's typed allocation or sourced allocation. Therefore, in this case, the type of elem in list_append() will be list_elem_t.
A quick fix would be to remove the allocate(elem) statement in list_append() and add a typed allocation statement before the call to append() in variable_register():
| Code: | allocate(var_1d_t::var)
call var_list%append(var) |
You could also incorporate this into the select type statement prior to the call to append() in variable_register():
| Code: |
select type (v=>var)
type is (var_1d_t)
allocate(var_1d_t::var)
print *, "---> Register a 1D variable """//trim(name)//"""."
type is (var_2d_t)
allocate(var_2d_t::var)
print *, "---> Register a 2D variable """//trim(name)//"""."
type is (var_t)
print *, "---> Oh, no!"
class default
print *, "---> Unknown variable type """//trim(name)//"""."
end select
call var_list%append(var) |
Note that the select type statement now uses an associate-name called "v" and a selector called "var" (i.e., select type(v=>var) versus select type(var) ). We need to use both an associate-name and a selector so we allocate the pointer "var", not the associate-name "var".
If the list_append() procedure had access to the var_1d_t and var_2d_t types (they're defined in the second file, not the first file), then you could move the select type and allocate statement into the list_append() procedure.
You could also use a wrapper routine in the second file that performs the select type/allocation prior to the call to list_append().
Finally, there's a PGI Insider article that covers generic linked lists. Feel free to check it out for other ideas on how to implement linked lists in Fortran. Below is the link to the article:
http://www.pgroup.com/lit/articles/insider/v3n2a2.htm
-Mark |
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