c mysql封装类

<?php
class MySQLDB {
    private $host;
    private $username;
    private $password;
    private $dbname;
    private $pdo;

    public function __construct($host, $username, $password, $dbname) {
        $this->host = $host;
        $this->username = $username;
        $this->password = $password;
        $this->dbname = $dbname;
        $this->connect();
    }

    private function connect() {
        try {
            $dsn = "mysql:host={$this->host};dbname={$this->dbname}";
            $this->pdo = new PDO($dsn, $this->username, $this->password);
            $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch (PDOException $e) {
            die("Connection failed: " . $e->getMessage());
        }
    }

    public function query($sql) {
        try {
            $stmt = $this->pdo->query($sql);
            return $stmt->fetchAll(PDO::FETCH_ASSOC);
        } catch (PDOException $e) {
            die("Query failed: " . $e->getMessage());
        }
    }

    public function close() {
        $this->pdo = null;
    }
}

// 使用示例
$db = new MySQLDB('localhost', 'root', 'password', 'testdb');
$result = $db->query('SELECT * FROM users');
print_r($result);
$db->close();
?>