我正在尝试编写一个简单的代码，该代码采用一些具有相同父抽象类的对象，将它们存储到二进制文件中并读回它们。
我的代码如下所示：
module m
implicit none
type :: container
class(a), allocatable :: item
end type container
type, abstract :: a
character(20), public :: obj_type
integer, public :: num
contains
procedure :: write_impl => write_a
procedure :: read_impl => read_a
generic :: write(unformatted) => write_impl
generic :: read(unformatted) => read_impl
end type a
type, extends(a) :: b
integer, public :: num2
contains
procedure :: write_impl => write_b
procedure :: read_impl => read_b
end type b
type, extends(a) :: c
end type c
contains
subroutine write_a(this, unit, iostat, iomsg)
class(a), intent(in) :: this
integer, intent(in) :: unit
integer, intent(out) :: iostat
character(*), intent(inout) :: iomsg
write(unit, iostat=iostat, iomsg=iomsg) this%num
end subroutine write_a
subroutine read_a(this, unit, iostat, iomsg)
class(a), intent(inout) :: this
integer, intent(in) :: unit
integer, intent(out) :: iostat
character(*), intent(inout) :: iomsg
read(unit, iostat=iostat, iomsg=iomsg) this%num
end subroutine read_a
subroutine write_b(this, unit, iostat, iomsg)
class(b), intent(in) :: this
integer, intent(in) :: unit
integer, intent(out) :: iostat
character(*), intent(inout) :: iomsg
write(unit, iostat=iostat, iomsg=iomsg) this%num, this%num2
end subroutine write_b
subroutine read_b(this, unit, iostat, iomsg)
class(b), intent(inout) :: this
integer, intent(in) :: unit
integer, intent(out) :: iostat
character(*), intent(inout) :: iomsg
read(unit, iostat=iostat, iomsg=iomsg) this%num, this%num2
end subroutine read_b
end module m
program mwe
use m
implicit none
class(a), allocatable :: o1, o2, o3, o4
class(container), allocatable :: arr(:)
integer :: i, arr_size, tmp
character(20) :: str_tmp
o1 = b('b', 1, 2)
o2 = c('c', 3)
allocate(arr(2))
arr(1)%item = o1
arr(2)%item = o2
select type(t => o1)
type is(b)
write(*,*) t%num, t%num2
end select
select type(t => arr(1)%item)
type is(b)
write(*,*) t%num, t%num2
end select
write(*,*) 'Write into binary'
! WRITE size
open(123, file='test5.dat', form='unformatted')
write(123) SIZE(arr)
do i=1,2
write(123) arr(i)%item%obj_type
if(arr(i)%item%obj_type .eq. 'b') then
select type(t => arr(i)%item)
type is(b)
write(123) t
end select
else if(arr(i)%item%obj_type .eq. 'c') then
select type(t => arr(i)%item)
type is(c)
write(123) t
end select
end if
end do
close(123)
write(*,*) 'Read from binary'
open(123, file='test5.dat', form='unformatted')
read(123) arr_size
write(*,*) 'array size: ', arr_size
do i=1,2
read(123) str_tmp
write(*,*) str_tmp
if(allocated(o3)) deallocate(o3)
if(str_tmp .eq. 'b') then
allocate(b :: o3)
select type(t => o3)
type is(b)
read(123) t
write(*,*) t%num, t%num2 ! BAD OUTPUT
end select
else if(str_tmp .eq. 'c') then
allocate(c :: o3)
select type(t => o3)
type is(c)
read(123) t
write(*,*) t%num
end select
end if
end do
end program mwe
问题是，读取o1- 它的类型是b，即这个对象有两个组件 -num和num2. 我存储它，我自然希望读取的值与写入的值相同。
但是我得到了与在 Fortran 数组中被删除的变量中描述的相同的奇怪行为？. 在那个问题中，它是由初始化数组时的错误赋值语法引起的，但在这种情况下，我完全不知道为什么我的输出看起来像这样：
1 2
1 2
Write into binary
Read from binary
array size: 2
b
1 0
c
3
下面的值b显然应该是 1 和 2，而不是 1 和 0。我做错了什么？