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Warning : mysqli_prepare() expects parameter 1 to be mysqli, null

What I have tried:


if(empty($username_err) && empty($password_err)){

global $link;
$sql = "SELECT id, username, password FROM users WHERE username = ?";

error line
if($stmt = mysqli_prepare($link, $sql))

And here is config.php

class dbConfig {
private $serverName = 'localhost';
private $userName = 'root';
private $password = '';
private $dbName = 'dg_db';
protected $conn;

public function __construct()

$link = mysqli_connect('localhost','root','','dg_db');


$dsn ="mysql:host={$this->serverName}; userName={$this->userName}; charset=utf8";
$this->conn = new PDO($dsn, $this->userName, $this->password, $options);


catch(PDOException $e)
echo "Connection Error: ".$e->getMessage();


Warning : mysqli_prepare() expects parameter 1 to be mysqli, null

I am stuck of this
Updated 17-May-21 21:16pm
Mohibur Rashid 18-May-21 3:19am    
yeah, your $link is null. You need to initiate $link. . Follow the example #1. Procedure style.

Never store passwords in clear text - it is a major security risk. There is some information on how to do it here: Password Storage: How to do it.[^] - the code is in C#, but the text explains why you do this. For PHP, there are built in methods for hashing passwords:[^]

And remember: if this is web based and you have any European Union users then GDPR applies and that means you need to handle passwords as sensitive data and store them in a safe and secure manner. Text is neither of those and the fines can be .... um ... outstanding. In December 2018 a German company received a relatively low fine of €20,000 for just that.
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Either you forgot to call __construct or the call to mysqli_connect failed for some reason. But since you do not check to see whether it succeeded any failure there will go unrealised.
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