这东东好像有很多人写过，不过看了几个都觉得不怎么漂亮，花了点时间实现了下面的函数，用起来还不错。
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; c/c++ header include guard
(defun insert-include-guard ()
  "insert include guard for c and c++ header file.
for file filename.ext will generate:
#ifndef FILENAME_EXT_
#define FILENAME_EXT_

original buffer content

#endif//FILENAME_EXT_
"
  (interactive)
  (setq file-macro
    (concat (replace-regexp-in-string "\\." "_" (upcase (file-name-nondirectory buffer-file-name))) "_"))
  (setq guard-begin (concat "#ifndef " file-macro "\n"
                "#define " file-macro "\n\n"))
  (setq guard-end
    (concat "\n\n#endif//" file-macro "\n"))
  (setq position (point))
  (goto-char (point-min))
  (insert guard-begin)
  (goto-char (point-max))
  (insert guard-end)
  (goto-char (+ position (length guard-begin))))