I primarily work on Linux, so I put this in my Emacs config:

; Linux mode for C
(setq c-default-style
'((c-mode . "linux") (other . "gnu")))

However, other projects like QEMU have their own style preferences. So here’s what I added to use a different style for that. First, I found the qemu C style defined here. Then, to only use this on some C code, we attach a hook that only overrides the default C style if the filename contains “qemu”, an imperfect but decent-enough test.

(defconst qemu-c-style
'((indent-tabs-mode . nil)
(c-basic-offset . 4)
(tab-width . 8)
(c-comment-only-line-offset . 0)
(c-hanging-braces-alist . ((substatement-open before after)))
(c-offsets-alist . ((statement-block-intro . +)
(substatement-open . 0)
(label . 0)
(statement-cont . +)
(innamespace . 0)
(inline-open . 0)
))
(c-hanging-braces-alist .
((brace-list-open)
(brace-list-intro)
(brace-list-entry)
(brace-list-close)
(brace-entry-open)
(block-close . c-snug-do-while)
;; structs have hanging braces on open
(class-open . (after))
;; ditto if statements
(substatement-open . (after))
;; and no auto newline at the end
(class-close)
))
)
"QEMU C Programming Style")

(c-add-style "qemu" qemu-c-style)

(defun maybe-qemu-style ()
(when (and buffer-file-name
(string-match "qemu" buffer-file-name))
(c-set-style "qemu")))

(add-hook 'c-mode-hook 'maybe-qemu-style)