Type or Class for a Pointer in a Linked List in Fortran -

i confused usage of type , class in defining linked list type bound procedure in fortran. following simple program causes segmentation fault in get_num_nodes function. however, if change declaration of pointer next class type, program ends normally.

the segmentation fault occurs when build ifort (version 14.0.2). if build gfortran (version 4.8.4 , 7.2.0), both cases of class , type end normally.

what wrong using class in declaring next pointer? how can understand problem? or, wrong in different part of code?

tll.f90

module tll   implicit none   private    public llnode, add_node_at_head    type llnode      private      integer                                  :: idx      !type(llnode),                   pointer :: next => null()      ! .. using declaration type works.      class(llnode),                   pointer :: next => null()      ! .. declaration class causes segmentation fault       ! ifort.     contains      procedure :: get_num_nodes   end type llnode  ! ================================================================ contains ! ================================================================    ! ****************************************************************   subroutine add_node_at_head(p_head, idx_arg)   ! ****************************************************************     type(llnode),     pointer, intent(inout) :: p_head     integer,                   intent(in)    :: idx_arg     !     type(llnode),  pointer :: p_new_head      write(*,*) 'entered add_node_at_head..'      allocate(p_new_head)     p_new_head%idx = idx_arg     p_new_head%next => p_head     p_head => p_new_head      write(*,*) '.. leaving add_node_at_head'    end subroutine add_node_at_head      ! ****************************************************************   function get_num_nodes(self) result(num_nodes)   ! ****************************************************************     integer                            :: num_nodes     class(llnode), target, intent(in)  :: self     !     class(llnode), pointer     :: p_node      write(*,*) 'entered get_num_nodes ..'      num_nodes = 0     p_node => self     while (associated(p_node))         num_nodes = num_nodes+1        p_node => p_node%next     end      write(*,*) '.. leaving get_num_nodes'    end function get_num_nodes   end module tll 

main.f90

program main   use tll, : llnode, add_node_at_head   implicit none    type(llnode),  pointer  :: p_head=>null()   integer                 :: num_nodes    call add_node_at_head(p_head, 10)   num_nodes= p_head%get_num_nodes()    write(*,*) 'num_nodes=', num_nodes    write(*,*) 'normal end.'  end program main 

compilation , execution:

$ ifort -c tll.f90 $ ifort -c main.f90 $ ifort -o exe main.o tll.o $ ./exe   entered add_node_at_head..  .. leaving add_node_at_head  entered get_num_nodes .. forrtl: severe (174): sigsegv, segmentation fault occurred image              pc                routine            line        source              exe                000000000046df09  unknown               unknown  unknown exe                000000000046c7de  unknown               unknown  unknown exe                000000000043e3b2  unknown               unknown  unknown exe                0000000000422fc3  unknown               unknown  unknown exe                0000000000402a3b  unknown               unknown  unknown libpthread.so.0    00002b8fdbb48330  unknown               unknown  unknown exe                00000000004026d2  unknown               unknown  unknown exe                0000000000402402  unknown               unknown  unknown exe                0000000000402336  unknown               unknown  unknown libc.so.6          00002b8fdbd77f45  unknown               unknown  unknown exe                0000000000402229  unknown               unknown  unknown $