Sample configuration to match the coding style in use.

In .emacs:

(custom-set-variables
 '(c-basic-indent 4)
 '(safe-local-variable-values
   (quote
    ((c-set-offset
      (quote innamespace)
      0)
     (c-set-style . "CC-MODE"))))
)
;; no indent in namespace
(defun my-c-setup ()
   (c-set-offset 'innamespace [0]))
(add-hook 'c++-mode-hook 'my-c-setup)


In .dir-local.el:

((nil . ((indent-tabs-mode . t)
         (tab-width . 4)
         (fill-column . 80)))
 (c-mode . ((c-basic-offset . 4)
            (c-set-style . "CC-MODE")))
 (c++-mode . ((c-basic-offset . 4)
              (c-set-style . "CC-MODE")))
 )