Fatal error: Using $this when not in object context in [duplicate] - php

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Fatal error: Using $this when not in object context
(4 answers)
Closed 9 years ago.
i have this class for connect to mysql database using php/mysqli:
class AuthDB {
private $_db;
public function __construct() {
$this->_db = new mysqli(DB_SERVER, DB_USER, DB_PASS, DB_NAME)
or die("Problem connect to db. Error: ". mysqli_error());
}
public function __destruct() {
$this->_db->close();
unset($this->_db);
}
}
now, i have any page for list user :
require_once 'classes/AuthDB.class.php';
session_start();
$this->_db = new AuthDB(); // error For This LINE
$query = "SELECT Id, user_salt, password, is_active, is_verified FROM Users where email = ?";
$stmt = $this->_db->prepare($query);
//bind parameters
$stmt->bind_param("s", $email);
//execute statements
if ($stmt->execute()) {
//bind result columnts
$stmt->bind_result($id, $salt, $pass, $active, $ver);
//fetch first row of results
$stmt->fetch();
echo $id;
}
now, i see this error:
Fatal error: Using $this when not in object context in LINE 6
How to fix this error?!

Answer 1

Like the error says, you can't use $this outside of the class definition. To use $_db outside the class definition, first make it public instead of private:
public $_db
Then, use this code:
$authDb = new AuthDb();
$authDb->_db->prepare($query); // rest of code is the same
--
You have to understand what $this actually means. When used inside a class definition, $this is used to refer to an object of that class. So if you had a function foo inside AuthDB, and you needed to access $_db from within foo, you would use $this to tell PHP that you want the $_db from the same object that foo belongs to.
You might want to read this StackOverflow question: PHP: self vs $this