program testoptional
    interface
        subroutine testsub(*,B,*,A,D,C,E,F)
            integer, optional :: C
            integer, optional :: E
        end subroutine
    end interface

    call testsub(200,2,200,1,4,3,5,6)

    call testsub(200,2,200,1,D=4,F=3)

200 print *, "hello, world!"
end program testoptional

subroutine testsub(*,B,*,A,D,C,E,F) !<<<<< 16,1,16,5,2,1,3,0,5,4,6,7,pass
    integer, optional :: C
    integer, optional :: E
end subroutine

subroutine testsub2
    interface
        subroutine testsub(*,B,*,A,D,C,E,F)
            integer, optional :: C
            integer, optional :: E
        end subroutine
    end interface

    call testsub(300,2,300,1,D=20,C=5,E=30,F=2)

300 print *, "world, hello!!"

end subroutine