How to tell emacs to open .h file in C++ mode?

Question

What lines should I add to my _emacs (on Windows) file to have it open .h files in C++ mode? The default is C mode.

Answer 1

Since I use both C and C++ regularly, I wrote this function to try and "guess" whether a .h file is meant to be C or C++

;; function decides whether .h file is C or C++ header, sets C++ by
;; default because there's more chance of there being a .h without a
;; .cc than a .h without a .c (ie. for C++ template files)
(defun c-c++-header ()
  "sets either c-mode or c++-mode, whichever is appropriate for
header"
  (interactive)
  (let ((c-file (concat (substring (buffer-file-name) 0 -1) "c")))
    (if (file-exists-p c-file)
        (c-mode)
      (c++-mode))))
(add-to-list 'auto-mode-alist '("\\.h\\'" . c-c++-header))

And if that doesn't work I set a key to toggle between C and C++ modes

;; and if that doesn't work, a function to toggle between c-mode and
;; c++-mode
(defun c-c++-toggle ()
  "toggles between c-mode and c++-mode"
  (interactive)
  (cond ((string= major-mode "c-mode")
         (c++-mode))
        ((string= major-mode "c++-mode")
         (c-mode))))

It's not perfect, there might be a better heuristic for deciding whether a header is C or C++ but it works for me.