Variable: c-insert-tab-function
c-insert-tab-function is a customizable variable defined in
cc-vars.el.gz.
Value
insert-tab
Documentation
Function used when inserting a tab for M-x c-indent-command (c-indent-command).
Only used when c-tab-always-indent indicates a real tab character
should be inserted. Value must be a function taking no arguments.
The default, insert-tab, inserts either a tab or the equivalent
number of spaces depending on the value of indent-tabs-mode(var)/indent-tabs-mode(fun).
Source Code
;; Defined in /usr/src/emacs/lisp/progmodes/cc-vars.el.gz
(defcustom c-insert-tab-function 'insert-tab
"Function used when inserting a tab for \\[c-indent-command].
Only used when `c-tab-always-indent' indicates a `real' tab character
should be inserted. Value must be a function taking no arguments.
The default, `insert-tab', inserts either a tab or the equivalent
number of spaces depending on the value of `indent-tabs-mode'."
:type 'function
:group 'c)