Function: hide-ifdef-mode

Toggle features to hide/show #ifdef blocks (Hide-Ifdef mode).
With a prefix argument ARG, enable Hide-Ifdef mode if ARG is
positive, and disable it otherwise. If called from Lisp, enable
the mode if ARG is omitted or nil.

Hide-Ifdef mode is a buffer-local minor mode for use with C and
C-like major modes. When enabled, code within #ifdef constructs
that the C preprocessor would eliminate may be hidden from view.
Several variables affect how the hiding is done:

An association list of defined and undefined symbols for the
current buffer. Initially, the global value of `hide-ifdef-env'
is used.

An association list of defined symbol lists.
Use `hide-ifdef-set-define-alist' to save the current `hide-ifdef-env'
and `hide-ifdef-use-define-alist' to set the current `hide-ifdef-env'
from one of the lists in `hide-ifdef-define-alist'.

Set to non-nil to not show #if, #ifdef, #ifndef, #else, and
#endif lines when hiding.

Indicates whether `hide-ifdefs' should be called when Hide-Ifdef mode
is activated.

Set to non-nil if you want to make buffers read only while hiding.
After `show-ifdefs', read-only status is restored to previous value. Uses keymap `hide-ifdef-mode-map', which is not currently defined. (fn &optional ARG)