how to use a variable outside a function - php

Question

i have this initialization file called init.php which I have declared a variable called $db for a mysqli connection. Below is my code.
<?php
ob_start();
session_start();
define('DBHOST', '127.0.0.1');
define('DBUSER', 'root');
define('DBPASSWORD', '');
define('DBNAME', 'mydb');
$db = new mysqli(DBHOST, DBUSER, DBPASSWORD, DBNAME);
if ($db->connect_error) {
header('Location: 404.php');
}
require_once 'functions/User.php';
require_once 'functions/Sanitize.php';
As you can see I required User.php inside the function folder, and on the User.php file i have this code
<?php
function login($idnumber, $username, $password) {
$idnumber = sanitize($idnumber);
$username = sanitize($username);
$password = sanitize($password);
$hashed_password = get_hashed_password($username);
}
function get_hashed_password($username) {
$username = sanitize($username);
$sql = "SELECT `password` FROM `users` WHERE `username` = ?";
$stmt = $db->prepare($sql);
if(!$stmt) {
echo 'invalid sql statement';
}
die();
}
On the get_hashed_password() function i used the variable $db but i got an error message saying
Notice: Undefined variable: db in D:\xampp\htdocs\sample\functions\User.php on line 15
Fatal error: Call to a member function prepare() on a non-object in D:\xampp\htdocs\sample\functions\User.php on line 15
Can someone help me how can I used the variable $db in any of my functions? Thanks in advance!

Answer 1

Call $db as global
function get_hashed_password($username) {
global $db;
//...
}

Answer 2

you can use $GLOBALS inside the function like this
$your_var = "something";
function abc()
{
$your_var = $GLOBALS['your_var'];
}
UPDATE 2 :
function get_hashed_password($username) {
$username = sanitize($username);
$sql = "SELECT `password` FROM `users` WHERE `username` = ?";
$db = $GLOBALS['db'];
$stmt = $db->prepare($sql);
if(!$stmt) {
echo 'invalid sql statement';
}
die();
}