cc-imenu-c-prototype-macro-regexp

cc-imenu-c-prototype-macro-regexp is a variable defined in `cc-menus.el'.
Its value is

nil

Documentation:
RE matching macro names used to conditionally specify function prototypes.

For example:

#ifdef __STDC__
#define _P(x) x
#else
#define _P(x) /*nothing*/
#endif

int main _P( (int argc, char *argv[]) )

A sample value might look like: `\(_P\|_PROTO\)'.