In emacs, how to disable comment auto-indent in C/C++?

Question

Sometimes I want to have temporary comments fully left justified on a line `(//)` or a block of lines `/* */`. However, `CC Mode` overrides this by auto-indenting upon typing the second key. In general, I like auto-indent for keywords, etc, but I would prefer it to be disabled for comments. (update: ie. I want to disable the way comment indentation is triggered by the c-electric- key-bindings, but comments should still indent normally othewise) I've tried putting these lines in `.emacs`, but it doesn't prevent the behaviour. ``` (c-electric-slash nil) (c-electric-star nil) ```

Accepted Answer

Short answer:

```
(eval-after-load 'cc-mode
  '(progn
     (define-key c-mode-base-map "/" 'self-insert-command)
     (define-key c-mode-base-map "*" 'self-insert-command)))
```

Here's how I go about it:

Find out the function bound to `/`: `C-h k /`

It says "/ runs the command c-electric-slash, which is an interactive compiled Lisp function in 'cc-cmds.el'".

(If you don't see the link to `cc-cmds.el`, then you don’t have the elisp sources installed. Assuming you're not on Windows, you can use your system’s package manager to install the `emacs-el` package and try again.)

Follow that link to open `cc-cmds.el`. Searching for `c-electric-slash` doesn't find anything other than the function definition, so the keys aren't bound in this file. Searching in `cc-mode.el` from this directory reveals:

```
(define-key c-mode-base-map "/" 'c-electric-slash)
```

Now we know the name of the "keymap" in which to override the `/` keybinding.

If you add something like this to your init file, you'll probably get an error on startup:

```
(define-key c-mode-base-map "/" 'self-insert-command)
```

...because your init file is loaded before cc-mode.el is, and `c-mode-base-map` is undefined. So we use `eval-after-load` (as at the top of my answer). The first argument, `'cc-mode`, has to match the `provide` statement at the very end of cc-mode.el. If you don't know what the `progn` means, do `C-h f progn`.

If you like this style of learning/discovering Emacs, you might consider reading my "How to learn Emacs".

In emacs, how to disable comment auto-indent in C/C++?

Solution

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