Is there a function in emacs that centers an input text and fills the line with the comment symbol as one would use it for headings in a file?

Question

I want to have a quick way of writing a heading in an arbitrary file. So in Emacs-lisp mode the selction of Heading in a file and a call of the function would result in:

;;;;;;;;;;;;;;;;;;;; Heading ;;;;;;;;;;;;;;;;;;;;

I.e. automatically filling the rest of the line with the comment symbol of the respective mode and the text being centered, surrounded by a space and the comment symbols. I am almost sure there is something alike, somewhere?

Edit: Okay I found the file newcomment.el, which defines comment-styles such as plain, indent, aligned, box etc. Where aligned should be what I am asking for. But how can I get it running?

FWIW, M-x center-line centers one or more lines of text, but without adding the comment chars. — Drew
– Drew, Commented Jul 26, 2018 at 16:04

Maxim Kim · Accepted Answer · 2018-07-25 12:52:53Z

While not exactly what you need but...

You can try comment-box command together with C-u 20 prefix (or whatever number you want):

You can also write your own function to do it (just grab the sources of the comment-box and try to adjust it to remove 1st and last comment lines + add padding you need).

...

Now, I had a look into the source code and here we are (not bullet-proof but):

The function to use:

(defun comment-fill-aligned (arg) "Comment out the current line using fill-column to pad and align with comment chars. For the fill-column set to 80 it should look like: elisp: ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; hello ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; c: /************************************* hello *************************************/ " (interactive "p") (comment-normalize-vars) (let* ((comment-style 'aligned) (beg (line-beginning-position)) (end (line-end-position)) (com-add (/ (- fill-column (- end beg)) 2))) (comment-region beg end (+ comment-add com-add))))

So eval the function and call it interactively with M-x comment-fill-aligned. It works for the current line.

Thanks! I was also working on it but struggling with learning the basics of lisp...I tried to set the comment style to align and the call comment-region, but I guess the lisp syntax is wrong..? (defun comment-for-heading (arg) "Comment selected region and move it to center surounded by comment symbols." (setq comment-style 'aligned) (comment-region ((/ fill-column 2) arg)) (setq comment-style 'indent) ) — stevosn
– stevosn, Commented Jul 25, 2018 at 13:37
it is better to use temporary binding with let form instead of setq here. And for comment-region usage -- you didn't provide correct parameters — Maxim Kim
– Maxim Kim, Commented Jul 25, 2018 at 13:53
I see.. I used your function and tweaked it a bit.. there was a different result for an even or odd number of characters in the line ;-) — stevosn
– stevosn, Commented Jul 25, 2018 at 14:29
I didn't try to make it perfect ;). Your solution most probably has an issue with odd number of characters and c-style comments — Maxim Kim
– Maxim Kim, Commented Jul 25, 2018 at 17:07

stevosn · Accepted Answer · 2018-07-25 14:34:38Z

I adjusted Maxim's code to produce the following function, which accounts for even and odd number of characters present in a line:

(defun comment-fill-aligned (arg) "Comment out the current line using fill-column to pad and align with comment chars." (interactive "p") (comment-normalize-vars) (let* ((comment-style 'aligned) (beg (line-beginning-position)) (end (line-end-position)) (com-add (/ (- fill-column (+ (- end beg) 2)) 2))) (comment-region beg end (+ comment-add com-add)) ) (end-of-line) (if (> (current-column) (+ fill-column 1)) (delete-backward-char 1) () ) (newline))

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Is there a function in emacs that centers an input text and fills the line with the comment symbol as one would use it for headings in a file?

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