anchor.diff:       ! 'status_message_length': Usable length of 'status_message_c'
        !    buffer.  Recommend at least 100.
        !
  -     ! 'status_message': Returns a message explaining the exit status.
  +     ! 'status_message': Returns a message (null-terminated C string)
  +     !    explaining the exit status.
        !
        ! 'status': Returns the exit status code, one of the
        !    LBFGSB_STATUS_* constants defined in enumeration above.
  
positive.code:     ! Locals
      integer :: length
  
      ! Find the length of the shorter string
      length = min(len(string_f), string_c_length)
      ! Copy no more than 'length' characters
      string_c = string_f(1:length)
      ! Fill rest of string (if any) with nulls
      string_c(length+1:string_c_length) = c_null_char
    end subroutine convert_f_c_string
  
  
negative.code:   ! 'status_message_length_c': Usable length of 'status_message_c'
    !    buffer.  Recommend at least 100.
    !
    ! 'status_message_c': Message (null-terminated C string) explaining
    !    the exit status.
    !
    ! 'debug_c': Output verbosity level where 0 means no output and larger
    !    values mean increasing output.
  