Incorrect value of region-end in function that calls replace-string

Question

I am writing a function to do replacements on a highlighted region. It appears that while region-end changes after each replace, the value is not correct. That is, it does not point to the last character of the initial highlighted region. I am using CUA. Here is a shortened version of my function.

(defun sql-cln ()
  (interactive)
  (progn
    (replace-string "\"" ""  nil (region-beginning) (region-end))
    (replace-string "\t" ""  nil (region-beginning) (region-end))
    (replace-string "\n" ""  nil (region-beginning) (region-end))
    (replace-regexp " +" " " nil (region-beginning) (region-end))
))

Here's the text I test it on.

   select x.group_id, g.loc_prefix"
            "  from station_group_xref x, station_group g"
            " where x.station_id = $1"
                "   and g.loc_grp = 1"
                "   and x.group_id = g.group_id

Answer 1

The problem is that you're using replace-string and replace-regexp. As the help string warns you, these functions are not meant to be used in a Lisp program. Instead you should run a loop around a search function and replace-match.

The specific difficulty you're facing is that these functions change the point and mark. They set the mark to the beginning of the region that is processed and the point ends up at the end of the last replacement, or at the beginning of the region if there is no replacement.

Setting a variable to the value of (region-end) would not work because these return integers, and the position of the end of the region changes as you make changes inside the region. If you want to make multiple passes, you need a marker. Alternatively, to work on a particular section of the buffer, narrow it to that section.

You can do the replacement in a single pass: search for the disjunction of all the possibilities, and replace accordingly.

(defun sql-cln (beg end)
  (interactive "r")
  (save-restriction
    (narrow-to-region beg end)
    (goto-char (point-min))
    (while (re-search-forward "[\t\n\"]+\\|  +" nil t)
      (replace-match (if (eq (char-after (1- (point))) ?\ ) " " "")))))

or

(defun sql-cln (beg end-pos)
  (interactive "r")
  (let ((end-marker (make-marker))))
    (set-marker end-marker end-pos)
    (goto-char beg)
    (while (re-search-forward "[\t\n\"]+\\|  +" end-marker t)
      (replace-match (if (eq (char-after (1- (point))) ?\ ) " " "")))))