无法连接数据库 MySql

我是PHP PDO的新手，我在配置上编写了以下代码.php

class DBConnect{
    /* defining constants for database connectivity  */
    private $host="127.0.0.1";
    private $user="root";
    private $pass="";
    private $dbname="sms-portal";
    private $dbh;
    private $error;
    public function __construct(){
        // set DSN
        $dsn='mysql:host='.$this->host.'dbname='.$this->dbname;
        //set Options
        $options= array(
            PDO::ATTR_PERSISTENT => true,
            PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
        );
        // Create New PDO instance
        try{
            $this->dbh=new PDO($dsn, $this->user, $this->pass, $options);
            //die("here");
        }
        // Catch any errors here
        catch(PDOException $e){
            $this->error=$e->getMessage();
        }   
    }
}

在处理本地主机并提交新用户注册表时，它向我显示以下警告消息。

Warning: PDO::__construct() [pdo.--construct]: 
php_network_getaddresses: getaddrinfo failed: 
No such host is known. in config.php on line 25
Warning: PDO::__construct() [pdo.--construct]: 
[2002] php_network_getaddresses: getaddrinfo failed: 
No such host is kn (trying to connect via tcp://127.0.0.1dbname=sms-portal:3306) 
    in config.php on line 25