Emacs global-set-key to C-TAB

Question

I'm trying to set a key-binding to Ctrl+TAB in Emacs. I used the following call:

(global-set-key (read-kbd-macro "C-TAB") 'my-func)

However, whenever I use it, I get a

<C-tab> is undefined

error message. Trying to set the binding to "C-tab" results in an error message.

How can I set my binding to C-TAB?

Answer 1

Instead of using read-kbd-macro, try using the more plain syntax?

;(global-set-key [(control tab)] 'my-func)

Perhaps the plainer syntax will make a difference?

More on read-kbd-macro and global-set-key.

Answer 2

(global-set-key [C-tab] 'my-func)

Answer 3

It's because you are using read-kbd-macro incorrectly. When you see what is bound to a key:

C-h k C-TAB

Emacs tells you:

<C-tab> is undefined.

You need to include the <> in your invocation of read-kbd-macro.

(global-set-key (read-kbd-macro "<C-tab>") 'my-func)

And, I don't know how to generate <C-TAB>, but it's not the same as <C-tab>.

(equal (kbd "<C-TAB>") (kbd "<C-tab>"))
->
nil

Answer 4

Unlike others have suggested, it is a good idea to use kbd (or read-kbd-macro which is basically the same thing) in case you ever want to use the same configuration files in other versions of Emacs; kbd works across several versions of Emacs and XEmacs, where the internal representation of key sequences are different.

(global-set-key (kbd "<C-tab>") 'my-func)

The input format used by read-kbd-macro is documented in the docstring of edmacro-mode:

• The special words RET, SPC, TAB, DEL, LFD, ESC, and NUL represent special control characters. The words must be written in uppercase.

• A word in angle brackets, e.g., <return>, <down>, or <f1>, represents a function key. (Note that in the standard configuration, the function key <return> and the control key RET are synonymous.) You can use angle brackets on the words RET, SPC, etc., but they are not required there.

This is written somewhat unfortunately; the TAB referred to in the first bullet point is the ASCII character for TAB, and adding the Control modifier does something nonsensical to it. When you press Control-Tab, Emacs sees it (via your windowing system; it will not work in a text terminal) as <tab> with a Control modifier, which you can represent as C-<tab> or <C-tab>.

Answer 5

Note that you can also call global-set-key interactively. You can then see the correct binding command with repeat-complex-command (see also KeybindingGuide):

1. M-x: global-set-key
2. Type the key combination you want

3. Use C-x ESC ESC (repeat-complex-command) to see the apropiate command. In your case I get:

   (global-set-key (quote [C-tab]) (quote my-func))