Rebinding C-S-s?

Question

I'm trying to set up C-S-s to run isearch-forward-symbol-at-point, but when I do the obvious step of:

(global-set-key [C-S-s] 'isearch-forward-symbol-at-point)

It doesn't work. It just does a normal incremental search. When I press C-h k, followed by C-S-s (to find out what it's actually doing) emacs tells me:

C-s (**translated from C-S-s**) runs the command isearch-forward (found in
global-map), which is an interactive compiled Lisp function in
‘isearch.el’.

I think my question is "How do I stop C-S-s from being translated so that I can rebind that key sequence to isearch-forward-symbol-at-point?"

(I read up on keymaps and translation a bit, but it's not clear to me which translation keymap I should be changing, or how to change it)(maybe local-/global-unset-key?)

Answer 1

Actually the problem is not the translation: if you had bound the key that you meant to bind, it would have precedence over the translation. The problem is that you didn't bind Ctrl+Shift+S.

There are several syntaxes for keyboard events and it can occasionally get confusing. You can use modifier prefixes like C- for Control and S- for Shift with function keys, but not with characters. Your binding is for a function key whose name is C-S-s, and has no practical effect since there is no such key on your keyboard. For a character, even with modifiers, you need to use a character literal.

(global-set-key [?\C-\S-s] 'isearch-forward-symbol-at-point)

Some modifier+character combinations can be expressed with a string instead of an array of characters, e.g. (global-set-key "\C-s" 'isearch-forward). But strings can only store characters with modifiers that result in another string character: the result has to be an ASCII character, or Meta plus an ASCII character, or a member of an extended character set such as Unicode. Other modifier combinations can be expressed through character constants, but these characters can't be put in strings.

Instead of using a character literal, you can build the key chord using a list containing the modifiers and, at the end, the base key.

(global-set-key [(control shift ?s)] 'isearch-forward-symbol-at-point)

Alternatively, you can use the kbd macro and let it build the key sequence from the usual user-visible syntax. It will figure out that C-S-s means a modified character S and not a function key.

(global-set-key (kbd "C-S-s") 'isearch-forward-symbol-at-point)