PHP 析构函数显示错误？

Question

我的类中连接到数据库的析构函数中显示错误，我尝试删除析构函数中的变量，但它也显示错误。这是代码:

class DB_CONNECT {
    function __construct() {
        $this->connect();
        echo "connected succesfully";
    }
    function __destruct() {
        $this->close();
    }

    function connect() {
        require_once __DIR__ . '/db_config.php';

        $con = mysqli_connect(DB_SERVER, DB_USER, DB_PASSWORD, DB_DATABASE) 
                or die(mysqli_error());
        if($con){
            echo "connected succesfully";
        }
        return $con;
    }

    function close() {
        mysqli_close($con);
    }
}

并且有错误消息:

mysqli_close() expects parameter 1 to be mysqli

Answer 1

在连接方法中，您没有将 mysqli 对象分配给实例变量。

在__destruct中，$con未定义/NULL，这解释了错误消息。

require_once __DIR__ . '/db_config.php';

class DB_CONNECT {
    private $conn;
    function __construct() {
        $this->connect();
    }

    function __destruct() {
        $this->close();
    }

    function connect() {
        $this->conn = mysqli_connect(DB_SERVER, DB_USER, DB_PASSWORD, DB_DATABASE) 
                          or die(mysqli_error());
        echo "connected succesfully";
    }

    function close() {
        mysqli_close($this->conn);
    }
}