Why do I have to strongly rotate the pointer twice

CHNzyf · January 19, 2021, 2:41am

embeddedt · January 19, 2021, 2:54am

kisvegabor · January 19, 2021, 2:30pm

These functions store their result in a pointer called res. But in this case, the result has const void * type. So a pointer to it has const void ** type.

Take a look at the very similar _lv_style_get_color() function:

github.com

lvgl/lvgl/blob/011f105038212fff7b4aeec9a81ea0a0da7ded0b/src/lv_core/lv_style.c#L621-L640


int16_t _lv_style_get_color(const lv_style_t * style, lv_style_property_t prop, void * v_res)
{
    lv_color_t * res = (lv_color_t *)v_res;
    if(style == NULL) return -1;
    if(style->map == NULL) return -1;
    int32_t id = get_property_index(style, prop);
    if(id < 0) {
        return -1;
    }
    else {
        _lv_memcpy_small(res, &style->map[id + sizeof(lv_style_property_t)], sizeof(lv_color_t));
        lv_style_attr_t attr_act;
        attr_act = get_style_prop_attr(style, id);

        lv_style_attr_t attr_goal;
        attr_goal = (prop >> 8) & 0xFF;

        return LV_STYLE_ATTR_GET_STATE(attr_act) & LV_STYLE_ATTR_GET_STATE(attr_goal);
    }
}