我在實習中做的練習涉及一個上傳頁面，一個表格頁面，它將輸出數據庫表的記錄和一個數據庫表。問題是，經過巨大的努力使所有連接良好，我遇到了一些麻煩，因為 index.php 頁面應該發送信息并且正在發送數組并保存數組而不是文件。下面是 index.php 頁面的 PHP 代碼： <?phpif (!isset($_POST['Enviar'])):  // This if will search if the $_POST variable already has anything or not.$allowed =  array('txt');   //This array contains the file types which are allowed.$uploadtime = time();$uploadfile = $_FILES['file_to_upload'];include 'db_connection.php';$sql="select * from uploads";$result = $conn->query($sql);$target_dir = "uploads/";   //variable that will save the name of the folder or way where the file will be saved.$target_file = $target_dir . basename($_FILES['file_to_upload']['name']); //NOTICE undefined index: file_to_upload... because it doesn't have any value safe there yet.$goon = 1;  //This variable is used to check if there is any error messages or if the program can go on.$ext = pathinfo( $_FILES["file_to_upload"]["name"], PATHINFO_EXTENSION); // This will use the OS to get the file extension.if(!in_array($ext,$allowed) ) {echo 'Erro: Ficheiro n?o permitido. <br> Por favor, verifique se o formato do ficheiro é txt.';$goon = 0;}   第二段代碼中的字段名稱是數據庫中的名稱。誰能告訴我在 index.php 頁面中收到此錯誤消息有什么問題：注意：第 66 行 C:\xampp\htdocs\16082019\index.php 中的數組到字符串轉換