Function CGGetActiveDisplayList 

pub unsafe extern "C-unwind" fn CGGetActiveDisplayList(
    max_displays: u32,
    active_displays: *mut CGDirectDisplayID,
    display_count: *mut u32,
) -> CGError

Available on crate features CGDirectDisplay and CGError only.

Safety

• active_displays must be a valid pointer or null.
• display_count must be a valid pointer or null.