Ah. I never use C++, so I wouldn't know. =)
From looking at the source of cc-mode, though, try adding the hook to c-mode-common-hook instead of c-mode-hook. That hook is being run by all modes in cc-mode: c-mode, c++-mode, objc-mode and java-mode.
To find out the current style, type C-: c-indentation-style RET.