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It is often useful to move point “temporarily” within a localized portion
of the program, or to switch buffers temporarily. This is called an
excursion, and it is done with the save-excursion special
form. This construct initially remembers the identity of the current
buffer, and its values of point and the mark, and restores them after the
completion of the excursion.
The forms for saving and restoring the configuration of windows are described elsewhere (see Window Configurations, and voir la section Frame Configurations).
The save-excursion 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 (voir la section Nonlocal Exits).
The save-excursion special form is the standard way to switch buffers
or move point within one part of a program and avoid affecting the rest of
the program. It is used more than 4000 times in the Lisp sources of Emacs.
save-excursion does not save the values of point and the mark for
other buffers, so changes in other buffers remain in effect after
save-excursion exits.
Likewise, save-excursion does not restore window-buffer
correspondences altered by functions such as switch-to-buffer. One
way to restore these correspondences, and the selected window, is to use
save-window-excursion inside save-excursion (voir la section Window Configurations).
The value returned by save-excursion is the result of the last form
in body, or nil if no body forms were given.
(save-excursion forms)
≡
(let ((old-buf (current-buffer))
(old-pnt (point-marker))
(old-mark (copy-marker (mark-marker))))
(unwind-protect
(progn forms)
(set-buffer old-buf)
(goto-char old-pnt)
(set-marker (mark-marker) old-mark)))
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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.
Voir la section 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. Voir la section The Mark.
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Ce document a été généré par Eric Reinbold le 13 Octobre 2007 en utilisant texi2html 1.78.