Customize indentation for Octave-mode

[Shiyuan]

Hi,
    I want to customize the indentation style so that the indentation uses
space instead of tab and each indentation level is 4  more spaces.  I
googled around and tried to use the following codes, but it's not
working--the indentation level seems to be 2 spaces instead of 4 spaces.
Should I use c-basic-offset in that case? Anything I missed? Thank you.

defun octave-my-setting ()
  (setq c-basic-offset 4)
  (setq indent-tabs-mode nil))
(add-hook 'octave-mode-hook 'octave-my-setting)