Underline the current line (function inside)

Underline the current line (function inside)

[Jean Louis]

This function is handy to underline the current line:

(defun underline-line ()
  "Underline the current line."
  (interactive)
  (let* ((start (line-beginning-position))
	 (end (line-end-position))
	 (length (- end start)))
    (end-of-line)
    (newline)
    (insert (make-string length ?=))
    (newline)))


When there is a line like this, a key binding or M-x underline-line
===================================================================

does that underlining as above.



Jean

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Re: Underline the current line (function inside)

[Eli Zaretskii]

> Date: Fri, 11 Jun 2021 17:32:26 +0300
> From: Jean Louis <bugs@gnu.support>
> 
> This function is handy to underline the current line:
> 
> (defun underline-line ()
>   "Underline the current line."
>   (interactive)
>   (let* ((start (line-beginning-position))
> 	 (end (line-end-position))
> 	 (length (- end start)))
>     (end-of-line)
>     (newline)
>     (insert (make-string length ?=))
>     (newline)))

This assumes that each character takes 1 column.  That is false in
general, because some characters have zero width on display, and some
others take closer to two columns.

You need to use string-width instead, or count columns instead of
buffer positions.

And, of course, all this assumes fixed-pitch font.

Re: Underline the current line (function inside)

[Jean Louis]

* Eli Zaretskii <eliz@gnu.org> [2021-06-11 17:53]:
> > Date: Fri, 11 Jun 2021 17:32:26 +0300
> > From: Jean Louis <bugs@gnu.support>
> > 
> > This function is handy to underline the current line:
> > 
> > (defun underline-line ()
> >   "Underline the current line."
> >   (interactive)
> >   (let* ((start (line-beginning-position))
> > 	 (end (line-end-position))
> > 	 (length (- end start)))
> >     (end-of-line)
> >     (newline)
> >     (insert (make-string length ?=))
> >     (newline)))
> 
> This assumes that each character takes 1 column.  That is false in
> general, because some characters have zero width on display, and some
> others take closer to two columns.
> 
> You need to use string-width instead, or count columns instead of
> buffer positions.
> 
> And, of course, all this assumes fixed-pitch font.

Thanks.

(defun underline-line ()
  "Underline the current line."
  (interactive)
  (let* ((start (line-beginning-position))
	 (end (line-end-position))
	 (length (string-width (buffer-substring-no-properties start end))))
    (end-of-line)
    (newline)
    (insert (make-string length ?=))
    (newline)))

Re: Underline the current line (function inside)

[Eli Zaretskii]

> Date: Fri, 11 Jun 2021 18:33:45 +0300
> From: Jean Louis <bugs@gnu.support>
> Cc: help-gnu-emacs@gnu.org
> 
> (defun underline-line ()
>   "Underline the current line."
>   (interactive)
>   (let* ((start (line-beginning-position))
> 	 (end (line-end-position))
> 	 (length (string-width (buffer-substring-no-properties start end))))
>     (end-of-line)
>     (newline)
>     (insert (make-string length ?=))
>     (newline)))

Right.  I suggest to try the alternative that uses current-column, it
will allow you to avoid consing a string, and I think will also be
faster.