In my .emacs i have put following for cuda highlighting:

(setq c-default-style '(("c++" . "linux")
                        (java-mode . "java")
                        (awk-mode . "awk")
                        (other . "gnu")))

(setq c-default-style "k&r"
      c-basic-offset 4)

;; Use C-Mode for CUDA
(add-to-list 'auto-mode-alist '("\\.cu\\'" . c-mode))

Indentation 4 spaces works for c-mode or c files but for cuda files indentation is set to 2 spaces.
Please help me in setting indentation for cuda files to 4 spaces. Thanks!

1 Answer 1


The "gnu" style sets c-basic-offset to 2, so that's where that's coming from.

As you have specific needs for a specific filename extension, I'd probably just define a derived mode to use with auto-mode-alist:

(define-derived-mode cuda-mode c-mode "CUDA"
  "CUDA mode."
  (setq c-basic-offset 4))

(add-to-list 'auto-mode-alist '("\\.cu\\'" . cuda-mode))

You might alternatively call c-set-style in the mode body, for some appropriate style, or even have an empty mode body and add an entry to c-default-style for the new mode, depending on which approach you think will be the easiest to maintain.

Note also that c-basic-offset is automatically buffer-local, so the following isn't doing anything useful for that variable:

(setq c-default-style "k&r"
      c-basic-offset 4)

You could use (setq-default c-basic-offset 4) if you want to, but it's probably sensible to leave the default value alone.

Lastly, ("c++" . "linux") looks to me to be invalid as an entry in the c-default-style alist. That list maps major mode symbols to style names, and "c++" is not a symbol (nor even the name of a major mode symbol). I doubt that entry is doing anything?

  • Thanks @phils for quick reply! I removed the code that I mention in the question and added you code in .emacs. Still indentation for cuda .cu files remains 2 spaces. I wonder why it is not 4 spaces indentation. Please help
    – skaushal
    Commented Aug 9, 2018 at 9:48
  • My suggested code works for me.
    – phils
    Commented Aug 9, 2018 at 11:53
  • Any suggestion to debug this issue?
    – skaushal
    Commented Aug 9, 2018 at 14:44
  • Run emacs -Q to disable non-standard libraries, and then evaluate my suggestion in the *scratch* buffer, and then test and confirm whether or not it works.
    – phils
    Commented Aug 9, 2018 at 21:16
  • If it still doesn't work under emacs -Q, then let me know which version of Emacs you're using. Confirm that the "CUDA" lighter is displayed in the mode line (or that C-h m indicates the *.cu buffer is in cuda-mode), and check what C-h v c-basic-offset shows you (when used in the *.cu buffer).
    – phils
    Commented Aug 9, 2018 at 21:16

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