Function fltk::app::set_raw_callback

pub unsafe fn set_raw_callback<W>(
    widget: &mut W, 
    data: *mut c_void, 
    cb: Option<fn(_: WidgetPtr, _: *mut c_void)>
) where
    W: WidgetExt, 

Set a widget callback using a C style API

Safety

The function involves dereferencing externally provided raw pointers