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Re: auto-indenting C++ files upon saving

From: Andreas Politz
Subject: Re: auto-indenting C++ files upon saving
Date: Fri, 19 Feb 2010 19:11:15 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)

Eric James Michael Ritz <address@hidden> 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
             (y-or-n-p "Indent buffer before saving ?"))
    (indent-region (point-min)

(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)


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