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diff --git a/lisp/progmodes/cmacexp.el b/lisp/progmodes/cmacexp.el
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+;; C macro expansion
+;; Copyright (C) 1988 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 1, or (at your option)
+;; any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to
+;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+
+(defvar c-macro-preprocessor "/lib/cpp"
+  "*Command to be used for C preprocessing.")
+
+(defvar c-macro-options nil
+  "*List of options to use in C preprocessing.
+Each string in the list becomes a separate argument to the preprocessor.
+These arguments precede the filename.
+Use the `-I' option here to specify directories for header files.")
+
+(defun c-macro-expand (beg end)
+  "Display the result of expanding all C macros occurring in the region.
+The expansion is entirely correct because it uses the C preprocessor.
+You can use the variables `c-macro-preprocessor' and `c-macro-options'
+to customize how preprocessing is done, or specify header file directories."
+  (interactive "r")
+  (let ((outbuf (get-buffer-create "*Macroexpansion*"))
+        (tempfile "%%macroexpand%%")
+        process
+        last-needed)
+    (save-excursion
+      (set-buffer outbuf)
+      (erase-buffer))
+    (setq process (apply 'start-process "macros" outbuf c-macro-preprocessor
+                         c-macro-options))
+    (set-process-sentinel process '(lambda (&rest x)))
+    (save-restriction
+      (widen)
+      (save-excursion
+        (goto-char beg)
+        (beginning-of-line)
+        (setq last-needed (point))
+        (if (re-search-backward "^[ \t]*#" nil t)
+            (progn
+              ;; Skip continued lines.
+              (while (progn (end-of-line) (= (preceding-char) ?\\))
+                (forward-line 1))
+              ;; Skip the last line of the macro definition we found.
+              (forward-line 1)
+              (setq last-needed (point)))))
+      (write-region (point-min) last-needed tempfile nil 'nomsg)
+      ;; Output comment ender in case last #-directive is inside a comment.
+      ;; Also, terminate any string that we are in.
+      (write-region "*//*\"*/\n" nil tempfile t 'nomsg)
+      (write-region beg end (concat tempfile "x") nil 'nomsg)
+      (process-send-string process (concat "#include \"" tempfile "\"\n"))
+      (process-send-string process "\n")
+      (process-send-string process (concat "#include \"" tempfile "x\"\n"))
+      (process-send-eof process))
+    (while (eq (process-status process) 'run)
+      (accept-process-output))
+    (delete-file tempfile)
+    (delete-file (concat tempfile "x"))
+    (display-buffer outbuf)
+    (save-excursion
+      (set-buffer outbuf)
+      (goto-char (point-max))
+      (forward-line -1)
+      (delete-region (point) (point-max))
+      (re-search-backward "\n# 1 ")
+      (forward-line 2)
+      (while (eolp) (delete-char 1))
+      (delete-region (point-min) (point)))
+    (display-buffer outbuf)))