Emacs auto-save on switch buffer

A couple of ideas.

First, if you find yourself invoking a command like save with a sufficiently high frequency, you might consider a shorter key binding for the command. For example, I also found myself having the same "twitch," so now I use f2 instead of C-x C-s for saving edits.

The function that I bind to f2 saves every unsaved buffer unconditionally. You might find it useful:

(defun force-save-all ()
    "Unconditionally saves all unsaved buffers."
    (interactive)
    (save-some-buffers t))

(global-set-key [f2] 'force-save-all)

Now, on to the main issue. You could try something like this (notice that force-save-all is called):

(defun my-switch-to-buffer (buffer)
    (interactive (list (read-buffer "Switch to buffer: " (cadr buffer-name-history) nil)))
    (force-save-all)
    (switch-to-buffer buffer))

(global-set-key "\C-xb" 'my-switch-to-buffer)

Of course, you could also bind the switch buffer functionality to another key, like a function key, so that it's a one press operation.

I thought that @seth had a great idea about using advice, but I noticed that the ELisp manual suggests that advice not be used for key bindings. I'm not quite sure why this is the case, but that's what the manual suggests FYI.

To expand on Seth's answer, I'd do this:

(defadvice switch-to-buffer (before save-buffer-now activate)
  (when buffer-file-name (save-buffer)))
(defadvice other-window (before other-window-now activate)
  (when buffer-file-name (save-buffer)))
(defadvice other-frame (before other-frame-now activate)
  (when buffer-file-name (save-buffer)))

The check for buffer-file-name avoids saving buffers w/out files. You need to figure out all the entry points you use for switching buffers that you care about (I'd also advise other-window).

I'm kind of new to emacs lisp myself but this works in my testing:

(defadvice switch-to-buffer (before save-buffer-now)
  (save-buffer))

(ad-activate 'switch-to-buffer)

It's kind of annoying though because it's called after EVERY buffer (like scratch). So, consider this answer a hint.

When you want to disable it, you'll need to call:

(ad-disable-advice 'switch-to-buffer 'before 'save-buffer-now)
(ad-activate 'switch-to-buffer)