This one goes to the XFree86 development team:
there's a mistake in the mentioned manpage, where it states that
XF86VidModeGetAllModeLines returns a pointer to an array of XF86...ModeInfo
structures, (and thus the parameter is declared as XF86..ModeInfo **. The
real situation is that is returns a pointer to an array of _pointers_ to
mode info structures, and the function prototype has *** (as opposed to
**) in <X11/extensions/xf86vmode.h>.
P.S. please excuse me if I misspelled the function name, the structure
name or the include file name -- I'm on a different machine now. But I
hope the info given is enough to find the thing.