I already had this in my .emacs file for c mode. So I added a set variable to support c++ style comments for C, see at the end. But it still doesn't work. any suggestions ? (setq c-default-style "linux-c-mode") (defun linux-c-mode ()   (interactive)   (c-mode)   (setq c-indent-level 8)   (setq c-brace-imaginary-offset 0)   (setq c-brace-offset -8)   (setq c-argdecl-indent 8)   (setq c-label-offset -8)   (setq c-continued-statement-offset 8)   (setq indent-tabs-mode nil)   (setq tab-width 4) ->  (setq comment-start "// ") ->  (setq comment-end " ")) Regards, Maindoor.