Function nstd_gui_window_set_icon 

pub unsafe extern "C" fn nstd_gui_window_set_icon(
    window: NSTDWindow,
    img: *const NSTDImage,
) -> c_int

Sets a window’s icon image. Parameters: NSTDWindow window - The window. const NSTDImage *const img - The icon image, null for default. Returns: int errc - Nonzero on error.