Function CFPreferencesGetAppBooleanValue 

pub unsafe extern "C-unwind" fn CFPreferencesGetAppBooleanValue(
    key: &CFString,
    application_id: &CFString,
    key_exists_and_has_valid_format: *mut u8,
) -> bool

Available on crate feature CFPreferences only.

Safety

key_exists_and_has_valid_format must be a valid pointer or null.