auto-indenting C++ files upon saving

auto-indenting C++ files upon saving

[Art Werschulz]

Hi.

I am trying to teach my students that they should auto-indent their C++
files before saving, by issuing the commands
  C-x h M-C-\
i.e., 
  (mark-whole-buffer)
  (indent-region)
However, they haven't trained their "muscle memory" to do this, i.e., to
automatically type the sequence 
  C-x M-C-\ C-x C-s
How can this be automated, so that a file gets auto-indented whenever
it's saved?

I thinking of something along the lines of
(setq auto-save-hook
     (lambda 
     (mark-whole-region)
     (indent-region)))
but this didn't seem to work.

Actually, I'd only want this to work in some situations, e.g., a file
whose name matches a certain pattern.  Said pattern would be stored in
some variable.

My emacs-lisp is very weak.  Suggestions?  Thanks!

-- 
Art Werschulz (8-{)}   "Metaphors be with you."  -- bumper sticker
GCS/M (GAT): d? -p+ c++ l++ u+ P++ e--- m* s n+ h f g+ w+ t+ r- 
Net: agw@dsm.fordham.edu http://www.dsm.fordham.edu/~agw
Phone:   Fordham U. (212) 636-6325, Columbia U. (646) 775-6035

Re: auto-indenting C++ files upon saving

[Eric James Michael Ritz]

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Art Werschulz wrote:
> [...]
>
> How can this be automated, so that a file gets auto-indented whenever
> it's saved?
>
> I thinking of something along the lines of
> (setq auto-save-hook
>      (lambda
>      (mark-whole-region)
>      (indent-region)))
> but this didn't seem to work.
>
> Actually, I'd only want this to work in some situations, e.g., a file
> whose name matches a certain pattern.  Said pattern would be stored in
> some variable.
>
> My emacs-lisp is very weak.  Suggestions?  Thanks!

You should be able to add a hook to ‘before-save-hook’ to be called on
save that will indent the file for you.  If you specifically want this
for C++ files then it may be easier to check the current major mode to
see if it is in c++-mode, compared to trying to match against file
names for C++ files.  Maybe something like this?

(add-hook 'before-save-hook
          (lambda ()
            (when (eq 'c++-mode (buffer-local-value 'major-mode (current-buffer)))
              (mark-whole-buffer)
              (indent-region))))

I’m not very confident about my Emacs Lisp either, so there may be a
better way to have save-related hooks for specific modes :)

- --
Eric James Michael Ritz
Cyber Sprocket Labs
(843) 225-3830
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Re: auto-indenting C++ files upon saving

[Andreas Politz]

Eric James Michael Ritz <Eric@cybersprocket.com> writes:

> Art Werschulz wrote:
>> [...]
>>
>> How can this be automated, so that a file gets auto-indented whenever
>> it's saved?
>>
>> I thinking of something along the lines of (setq auto-save-hook
>>      (lambda (mark-whole-region) (indent-region)))
>> but this didn't seem to work.
>>
>> Actually, I'd only want this to work in some situations, e.g., a file
>> whose name matches a certain pattern.  Said pattern would be stored
>> in some variable.
>>
>> My emacs-lisp is very weak.  Suggestions?  Thanks!
>
> You should be able to add a hook to ‘before-save-hook’ to be called on
> save that will indent the file for you.  If you specifically want this
> for C++ files then it may be easier to check the current major mode to
> see if it is in c++-mode, compared to trying to match against file
> names for C++ files.  Maybe something like this?
>
> (add-hook 'before-save-hook
>           (lambda ()
>             (when (eq 'c++-mode (buffer-local-value 'major-mode
>             (current-buffer)))
>               (mark-whole-buffer) (indent-region))))
>
> I’m not very confident about my Emacs Lisp either, so there may be a
> better way to have save-related hooks for specific modes :)
>


I think it's better style to use a buffer-local hook.

(defun c++-indent-buffer-maybe ()
  (when (and (string-match
              "\\(foo\\|bar\\)\\.cpp\\'"
              (buffer-file-name))
             (y-or-n-p "Indent buffer before saving ?"))
    (indent-region (point-min)
                   (point-max))))

(defun my-c++-hook ()
  (add-hook 'before-save-hook 'c++-indent-buffer-maybe nil t))

Here the last argument `t' makes the hook local to the buffer.

(add-hook 'c++-mode-hook 'my-c++-hook)

-ap

Re: auto-indenting C++ files upon saving

[Richard Riley]

Art Werschulz <agw@dsm.fordham.edu> writes:

> Hi.
>
> I am trying to teach my students that they should auto-indent their C++
> files before saving, by issuing the commands
>   C-x h M-C-\
> i.e., 
>   (mark-whole-buffer)
>   (indent-region)
> However, they haven't trained their "muscle memory" to do this, i.e., to
> automatically type the sequence 
>   C-x M-C-\ C-x C-s
> How can this be automated, so that a file gets auto-indented whenever
> it's saved?

As a point of contention, I don't think you should do this when you
save. When you save you should be saving what you see. Students should
be indenting as they go.

Another reason is that people often save periodically anyway as they
edit - it would really annoy me if suddenly the program took it on
itself to re-indent the block I was working on.

As for putting it on auto-save this is even worse - it can auto-save
while you are typing and cause significant disruption.

>
> I thinking of something along the lines of
> (setq auto-save-hook
>      (lambda 
>      (mark-whole-region)
>      (indent-region)))
> but this didn't seem to work.

Is mark-whole-region a function?

>
> Actually, I'd only want this to work in some situations, e.g., a file
> whose name matches a certain pattern.  Said pattern would be stored in
> some variable.
>
> My emacs-lisp is very weak.  Suggestions?  Thanks!

At the minimum if you want auto-save-hook (I dont think its a good idea)
you should save your point etc (save-excursion) before doing the rest.

regards,

r.

Re: auto-indenting C++ files upon saving

[Torsten Mueller]

Richard Riley <rileyrgdev@gmail.com> schrieb:

> > How can this be automated, so that a file gets auto-indented
> > whenever it's saved?
>
> As a point of contention, I don't think you should do this when you
> save. When you save you should be saving what you see. Students
> should be indenting as they go.

I agree with this completely. For me it would be horror to get noticed
that any automatic process in the background modified my sources and I
cannot control it. If this really has to be done for any reason I
would prefer if this would happen in front of my eyes while I'm
editing. (Indeed I'm also not a fan of this, I want the text to be
what I type in, not what any dumb tool thinks it should be.)

T.M.