How can I make emacs highlight lines that go over 80 chars?

Question

I know there are solutions to making emacs show the 80 line column, but I don\'t want that sort of visual disturbance. I\'d just like to make it highlight a line if it\'s ov

Answer 1

Here is some example code which will highlight text that lies beyond column 80 with the current 'warning' face, and a line to enable it for C++ mode.

;; Turn on warn highlighting for characters outside of the 'width' char limit
(defun font-lock-width-keyword (width)
  "Return a font-lock style keyword for a string beyond width WIDTH
   that uses 'font-lock-warning-face'."
  `((,(format "^%s\\(.+\\)" (make-string width ?.))
     (1 font-lock-warning-face t))))

(font-lock-add-keywords 'c++-mode (font-lock-width-keyword 80))

It doesn't highlight the whole line, but I find it is reasonably helpful.