Dear Andre and Dominique,

I have found that LOC is returning the address of the class container
rather than the _data component for class scalars. See the source
below, which you will recognise! A fix is attached.

Note that the scalar allocate fails with MOLD= and so I substituted SOURCE=.

Cheers

Paul

    class(*), allocatable :: a(:), e ! Change 'e' to an array and
second memcpy works correctly
                                     ! Problem is with loc(e), which
returns the address of the
                                     ! class container.
    allocate (e, source = 99.0)
    allocate (a(2), source = [1.0, 2.0])
    call add_element_poly (a,e)
    select type (a)
      type is (real)
        print *, a
    end select

contains

    subroutine add_element_poly(a,e)
      use iso_c_binding
      class(*),allocatable,intent(inout),target :: a(:)
      class(*),intent(in),target :: e
      class(*),allocatable,target :: tmp(:)
      type(c_ptr) :: dummy

      interface
        function memcpy(dest,src,n) bind(C,name="memcpy") result(res)
          import
          type(c_ptr) :: res
          integer(c_intptr_t),value :: dest
          integer(c_intptr_t),value :: src
          integer(c_size_t),value :: n
        end function
      end interface

      if (.not.allocated(a)) then
        allocate(a(1), source=e)
      else
        allocate(tmp(size(a)),source=a)
        deallocate(a)
        allocate(a(size(tmp)+1),source=e) ! mold gives a segfault
        dummy = memcpy(loc(a(1)),loc(tmp),sizeof(tmp))
        dummy = memcpy(loc(a(size(tmp)+1)),loc(e),sizeof(e))
      end if
    end subroutine
end