anchor.diff:    ! 'status_message_length_c': Usable length of 'status_message_c'
     !    buffer.  Recommend at least 100.
     !
  -  ! 'status_message_c': Message explaining the exit status.
  +  ! '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.
  
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': Usable length of 'status_message_c'
       !    buffer.  Recommend at least 100.
       !
       ! '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.
  