Mark position from C

Mark position from C

[Po Lu]

Is there a canonical C function to obtain the position of mark?  Right
now, I'm doing this to compare mark against point, which looks wrong.

      && XMARKER (BVAR (current_buffer, mark))->position
      && marker_position (BVAR (current_buffer,
				mark)) == PT)

Re: Mark position from C

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Date: Wed, 15 Feb 2023 19:10:26 +0800
> 
> Is there a canonical C function to obtain the position of mark?  Right
> now, I'm doing this to compare mark against point, which looks wrong.
> 
>       && XMARKER (BVAR (current_buffer, mark))->position
>       && marker_position (BVAR (current_buffer,
> 				mark)) == PT)

marker_position (BVAR (current_buffer, mark)) is it.  Why does it look
wrong to you?

And why do you need the first condition?

And why do you need to access the mark in the first place?  It is rare
for the C code to need that; about the only place where we do it is in
interpreting the 'interactive' codes.

Re: Mark position from C

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

> marker_position (BVAR (current_buffer, mark)) is it.  Why does it look
> wrong to you?

What if the buffer's mark marker does not point into a buffer, or points
into the wrong buffer (is the latter even possible?)

> And why do you need the first condition?

Sorry, that should've been

  XMARKER (BVAR (current_buffer, mark))->buffer

Re: Mark position from C

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: emacs-devel@gnu.org
> Date: Thu, 16 Feb 2023 09:24:36 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > marker_position (BVAR (current_buffer, mark)) is it.  Why does it look
> > wrong to you?
> 
> What if the buffer's mark marker does not point into a buffer

marker_position signals an error in that case.

> or points into the wrong buffer (is the latter even possible?)

What do you mean by "wrong buffer"?

Re: Mark position from C

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

> What do you mean by "wrong buffer"?

Some other buffer, i.e. if someone does this:

  (set-marker (mark-marker) 0 (get-buffer-create "*the wrong buffer*"))

Re: Mark position from C

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: emacs-devel@gnu.org
> Date: Thu, 16 Feb 2023 16:48:58 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > What do you mean by "wrong buffer"?
> 
> Some other buffer, i.e. if someone does this:
> 
>   (set-marker (mark-marker) 0 (get-buffer-create "*the wrong buffer*"))

Did you see what happens if you do that?

Re: Mark position from C

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Po Lu <luangruo@yahoo.com>
>> Cc: emacs-devel@gnu.org
>> Date: Thu, 16 Feb 2023 16:48:58 +0800
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> > What do you mean by "wrong buffer"?
>> 
>> Some other buffer, i.e. if someone does this:
>> 
>>   (set-marker (mark-marker) 0 (get-buffer-create "*the wrong buffer*"))
>
> Did you see what happens if you do that?

Yes... the mark now points to the wrong buffer.

Anyway, I think I've figured this out now.  Thanks.