regex - Adding syntax highlighting for a comment section in Emacs

I have the following

(defun add-c-syntax-highlighting ()
  (font-lock-add-keywords nil '(
    ("\\<\\(\\-+\\)"   1 font-lock-warning-face prepend)
    ("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend))))

with

(add-hook 'c-mode-common-hook 'add-c-syntax-highlighting)

Testing on this simple buffer yields seemingly contradictory results:

//FIXME:
//-------------

with only FIXME fontified. What am I doing wrong?

Answer

My crystal ball tells me what you do wrong is copy&paste code you don't understand. Looks like it's feeling sarcastic today, sorry, I promise I'll get a new one soon.

As for your problem, it's the \\< in your regexp, which is a special constructor which matches the beginning of a word, so it can never match in front of a - since words can only start with proper letters or digits.