mysqli_real_escape_string() expects parameter 1 to be mysqli; mysql_result() expects parameter 1 to be resource - mysqli

Question

I'm getting these errors:
Notice: Undefined variable: link in login.php on line 11
Warning: mysqli_real_escape_string() expects parameter 1 to be mysqli,
null given in login.php on line 11
Notice: Undefined variable: link in login.php on line 18
Warning: mysqli_query() expects parameter 1 to be mysqli, null given
in login.php on line 18
Warning: mysql_result() expects parameter 1 to be resource, null given
in login.php on line 19
Here's the code:
<?php
session_start();
$link = mysqli_connect('localhost','root','') or die();
mysqli_select_db($link,'lr') or die();
function sanitize($data) {
return mysqli_real_escape_string($link, $data); <<line 11
}
function user_exists($username) {
$username = sanitize($username);
$query = mysqli_query($link, "SELECT COUNT('user_id') FROM 'users' WHERE 'username' = '$username'"); <<line 18
return (mysql_result($query, 0) ==1) ? true : false; <<line19
}
if (empty($_POST) === false) {
$username = $_POST['username'];
$password = $_POST['password'];
if (empty($username) === true || empty($password) === true) {
$errors[] = 'You need to enter a username and password';
} else if (user_exists($username) === false) {
$errors[] = 'User not found';
}
}
?>
What's the problem?

Answer 1

You need to use $_GLOBALS['link'] inside function.
Like this:
function sanitize($data) {
return mysqli_real_escape_string($_GLOBALS['$link'], $data); <<line 11
}
Same thing inside user_exist function.

Answer 2

Global may have worked to fix the problem, but it's better to pass the variable into the function.
function sanitize($data, $A) {
return mysqli_real_escape_string($A, $data); <<line 11
}
function user_exists($username, $A) {
$username = sanitize($username);
$query = mysqli_query($A, "SELECT COUNT('user_id') FROM 'users' WHERE 'usernam' = '$username'"); <<line 18
return (mysql_result($query, 0) ==1) ? true : false; <<line19
}
if (empty($_POST) === false) {
$username = $_POST['username'];
$password = $_POST['password'];
if (empty($username, $link) === true || empty($password) === true) {
$errors[] = 'You need to enter a username and password';
} else if (user_exists($username, $link) === false) {
$errors[] = 'User not found';
}
}