I'd like to know if it is possible the buffer is saved at the exact moment of modification; at the instant of the key up event.
I had the same requirement and auto-save feature of emacs hasn't worked well for me because it can't addadvice to c functions. So, I wrote a package real-auto-save for that. It is available on melpa.
You can install it by
M-x package-install RET real-auto-save
and in your config you can add
(require 'real-auto-save) (add-hook 'prog-mode-hook 'real-auto-save-mode) (setq real-auto-save-interval 1) ;; in seconds
After every second, if your buffer is modified, it will be saved automatically.
If you specifically want to save after key up event, you can write a lisp function for that.
You can enable
auto-save-mode, so Emacs automatically saves your current buffer in a different file. Then, add this function to
auto-save-hook to also write it directly on the actual file you are editing:
(defun save-buffer-if-visiting-file (&optional args) "Save the current buffer only if it is visiting a file" (interactive) (if (and (buffer-file-name) (buffer-modified-p)) (save-buffer args))) (add-hook 'auto-save-hook 'save-buffer-if-visiting-file)
According to the Emacs manual on auto-save control:
The variable auto-save-interval specifies how many characters there are between auto-saves. By default, it is 300. Emacs doesn’t accept values that are too small: if you customize auto-save-interval to a value less than 20, Emacs will behave as if the value is 20.
So, if you want Emacs to save for every key press, change
(setq auto-save-interval 1)