tabs - Getting Emacs to untabify when saving certain file types (and only those file types)

Question

I have the following in my .emacs file:

 (defun c++-mode-untabify ()
   (save-excursion
     (goto-char (point-min))
     (while (re-search-forward "[ ]+$" nil t)
       (delete-region (match-beginning 0) (match-end 0)))
     (goto-char (point-min))
     (if (search-forward "" nil t)
         (untabify (1- (point)) (point-max))))
   nil)

 (add-hook 'c++-mode-hook
           '(lambda ()
              (make-local-hook 'write-contents-hooks)
              (add-hook 'write-contents-hooks 'c++-mode-untabify)))

Mostly ripped off from http://www.jwz.org/doc/tabs-vs-spaces.html. This causes emacs to run untabify on the buffer before saving a C++ file.

The problem is that after I have loaded a C++ file, the untabify hook is being applied to all subsequent file writes, even for buffers of other file types. This means that if I open a C++ file and then edit, say, a tab-delimited text file, the tabs get clobbered when saving the file.

I'm not an elisp guru, but I think the (make-local-hook 'write-contents-hooks) line is trying to make the addition to write-contents-hooks apply only to the local buffer. However, it isn't working, and c++-mode-untabify is in write-contents-hooks for all buffers.

I'm using EmacsW32 22.0 on a Windows XP box. Does anyone have any idea how to make the write-contents-hooks change local to a specific buffer or how to reset it to nil when switching to other, non-C++ buffers?

Answer 1

write-contents-hooks is also obsolete. This is what you're after:

(add-hook 'c++-mode-hook
      '(lambda ()
         (add-hook 'before-save-hook
                   (lambda ()
                     (untabify (point-min) (point-max))))))

This is distilled from what I use, which does a few other things and is abstracted out to work with programming-specific modes:

(defun untabify-buffer ()
  "Untabify current buffer"
  (interactive)
  (untabify (point-min) (point-max)))

(defun progmodes-hooks ()
  "Hooks for programming modes"
  (yas/minor-mode-on)
  (add-hook 'before-save-hook 'progmodes-write-hooks))

(defun progmodes-write-hooks ()
  "Hooks which run on file write for programming modes"
  (prog1 nil
    (set-buffer-file-coding-system 'utf-8-unix)
    (untabify-buffer)
    (copyright-update)
    (maybe-delete-trailing-whitespace)))

(defun delete-trailing-whitespacep ()
  "Should we delete trailing whitespace when saving this file?"
  (save-excursion
    (goto-char (point-min))
    (ignore-errors (next-line 25))
    (let ((pos (point)))
      (goto-char (point-min))
      (and (re-search-forward (concat "@author +" user-full-name) pos t) t))))

(defun maybe-delete-trailing-whitespace ()
  "Delete trailing whitespace if I am the author of this file."
  (interactive)
  (and (delete-trailing-whitespacep) (delete-trailing-whitespace)))

(add-hook 'php-mode-hook 'progmodes-hooks)
(add-hook 'python-mode-hook 'progmodes-hooks)
(add-hook 'js2-mode-hook 'progmodes-hooks)