3

I have C comments like this:

/******************************************************************************
 *                   Includes                                                 *
 ******************************************************************************/

I want to be able to center within the *'s like this:

/******************************************************************************
 *                                  Includes                                  *
 ******************************************************************************/

I've been unable to do this. If I try M-x narrow-to-region and use M-x center-line, it deletes all the spaces on the right hand side instead of preserving them. Using M-x picture-mode does not improve matters. I tried moving to the fill column using M-x move-to-column hoping it would fill in the spaces, but it stops at the current length in both picture and non-picture mode.

Improve this question
2
  • There's rebox which looks quite powerful. 8 years old, so handle with care. There's rebox2 in melpa. Commented Jun 30, 2020 at 16:38
  • @Juancho does Rebox have any documentation? It looks like you have to set a numeric style for comments, and it's some number, but I can't find the number assignments. I played around it with but couldn't get it to work. Commented Jul 7, 2020 at 13:23

1 Answer 1

Reset to default
0

I never found what I was looking for, so I ended up hacking the center-line elisp code like so:

(defun c-center-comment (&optional nlines)
  "Center the boxed comment point is on, within the width specified by `fill-column'.
This means adjusting the space around the comment enclosed by asterisks (*) so that it equals
the distance between the end of the text and `fill-column'.
The argument NLINES says how many lines to center."
  (interactive "P")
  (if nlines (setq nlines (prefix-numeric-value nlines)))
  (while (not (eq nlines 0))
    (save-excursion
      (let ((lm (current-left-margin))
        line-length)
    (beginning-of-line)
        (delete-char 1)
    (delete-horizontal-space)
    (end-of-line)
        (forward-char -1)
        (delete-char 1)
    (delete-horizontal-space)
    (setq line-length (current-column))
    (if (> (- fill-column lm line-length) 0)
        (progn (indent-line-to
                 (+ lm (/ (- (- fill-column 1) lm line-length) 2)))
              (beginning-of-line)
              (if (< (% (- (- fill-column 1) lm line-length) 2) 1)
                    (delete-char 1))
              (insert-char ?\*)
              (end-of-line)
              (insert-char ?\ (+ lm (/ (- (- fill-column 1) lm line-length) 2)))
              (insert-char ?\*)))))
    (cond ((null nlines)
       (setq nlines 0))
      ((> nlines 0)
       (setq nlines (1- nlines))
       (forward-line 1))
      ((< nlines 0)
       (setq nlines (1+ nlines))
       (forward-line -1)))))

Note that this is very primitive. It assumes the line already starts and ends with an asterisk (change the insert-char commands to modify the character). If you want to center a new line, surround it with any sacrificial character, but I only wrote this for fixing existing comments, not for composing new ones.

Improve this answer

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.