Next: , Previous: , Up: Positions   [Contents][Index]

29.3 Excursions

It is often useful to move point “temporarily” within a localized portion of the program. This is called an excursion, and it is done with the save-excursion special form. This construct remembers the initial identity of the current buffer, and its values of point and the mark, and restores them after the excursion completes. It is the standard way to move point within one part of a program and avoid affecting the rest of the program, and is used thousands of times in the Lisp sources of Emacs.

If you only need to save and restore the identity of the current buffer, use save-current-buffer or with-current-buffer instead (see Current Buffer). If you need to save or restore window configurations, see the forms described in Window Configurations and in Frame Configurations.

Special Form: save-excursion body…

This special form saves the identity of the current buffer and the values of point and the mark in it, evaluates body, and finally restores the buffer and its saved values of point and the mark. All three saved values are restored even in case of an abnormal exit via throw or error (see Nonlocal Exits).

The value returned by save-excursion is the result of the last form in body, or nil if no body forms were given.

Because save-excursion only saves point and mark for the buffer that was current at the start of the excursion, any changes made to point and/or mark in other buffers, during the excursion, will remain in effect afterward. This frequently leads to unintended consequences, so the byte compiler warns if you call set-buffer during an excursion:

Warning: Use `with-current-buffer' rather than

To avoid such problems, you should call save-excursion only after setting the desired current buffer, as in the following example:

(defun append-string-to-buffer (string buffer)
  "Append STRING to the end of BUFFER."
  (with-current-buffer buffer
      (goto-char (point-max))
      (insert string))))

Likewise, save-excursion does not restore window-buffer correspondences altered by functions such as switch-to-buffer.

Warning: Ordinary insertion of text adjacent to the saved point value relocates the saved value, just as it relocates all markers. More precisely, the saved value is a marker with insertion type nil. See Marker Insertion Types. Therefore, when the saved point value is restored, it normally comes before the inserted text.

Although save-excursion saves the location of the mark, it does not prevent functions which modify the buffer from setting deactivate-mark, and thus causing the deactivation of the mark after the command finishes. See The Mark.

Next: , Previous: , Up: Positions   [Contents][Index]