我是PHP新手。我有这段代码，我想传递在函数中定义的名为$sum的全局变量post_order to功能update_custom_meta. 还是没有运气。我做错了什么？提前感谢您！

function post_order() {
    $args = array(
        \'type\' => \'shop_order\',
        \'status\' => \'processing\',//zmienić//zmienić na completed
        \'return\' => \'ids\',
        \'date_created\' => ( date("F j, Y", strtotime( \'-2 days\' ) ) ),
    );

    $orders_ids = wc_get_orders( $args );

    foreach ($orders_ids as $order_id) {
        $order = new WC_Order( $order_id );
        $items = $order->get_items();
        global $sum;
        foreach ( $items as $item ) {
            $product_id = $item->get_product_id();
            if($product_id == $_GET[\'post\']) {
                $product_qty = $item->get_quantity();
                $sum += $product_qty;
            }
        }
    }
}    

add_action(\'init\', \'post_order\'); 

function update_custom_meta() {
    global $post_id;
    echo $sum;
    $custom_value = $_POST[\'auto_restock_value\'] - $sum;
    update_post_meta($post_id, \'auto_restock_value\', $custom_value);
    //get_post_meta($post -> ID, \'daily_restock_amount\', true);
    update_post_meta($post_id, \'_stock\', $custom_value);
}

function update_cart_stock() {
    global $post_id;
    //echo get_post_meta($post_id, \'total_sales\', true);
    update_post_meta($post_id, \'_stock\', $custom_value);
}

add_action( \'save_post\', \'update_custom_meta\' , 10, 2 );