PHP variable scope issue with mysqli - php

Question

I am still learning PHP and I'm trying to get around this error I'm getting.
As per this link my code is correct, but this is my code and this is the error i'm receiving:
$con = mysqli_connect("IP","username","passowrd","dbname");
// Check connection
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
function get_demos(){
$result = mysqli_query($con,"SELECT * FROM demos");
if(!$result)
{
die("Invalid query ".mysqli_error($con));
}
return $result;
}
get_demos();
Warning: mysqli_query() expects parameter 1 to be mysqli, null given in /home/content/83/11483383/html/php/db.php on line 10
Warning: mysqli_error() expects parameter 1 to be mysqli, null given
in /home/content/83/11483383/html/php/db.php on line 13 Invalid query
What am I doing wrong?
Thanks.

Answer 1

You should try like,
$con = mysqli_connect("IP","username","passowrd","dbname");
// Check connection
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
function get_demos($con){
$result = mysqli_query($con,"SELECT * FROM demos");
if(!$result)
{
die("Invalid query ".mysqli_error($con));
}
return $result;
}
get_demos($con);

Answer 2

You are not declaring that a variable $con is already set.
Try this one
$con = mysqli_connect('localhost', 'root', '');
mysqli_select_db($con, 'databse_name_here') or die ('Failed to connect to MySQL: ' . mysqli_connect_error());
function get_demos($con){
$result = mysqli_query($con,"SELECT * FROM users");
if(!$result)
{
die("Invalid query ".mysqli_error($con));
}
return $result;
}
get_demos($con);

Answer 3

You have to pass your connection to your function. if you don't want to do it every time you can use singleton pattern to always have it in scope.
class DBCon {
private static $_instance = null;
private function __construct() {
$_instance = mysqli_connect("IP","username","passowrd","dbname");
// Check connection
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
}
public static function get() {
if(is_null(self::$_instance)) {
self::$_instance = new DBCon();
}
return self::$_instance;
}
}
and use it in your code :
function get_demos(){
$result = mysqli_query(DBCon::get(),"SELECT * FROM demos");
if(!$result)
{
die("Invalid query ".mysqli_error(DBCon::get()));
}
return $result;
}

Answer 4

I figured out the solution after putting the question:
$con = mysqli_connect("IP","username","passowrd","dbname");
// Check connection
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
function get_demos(){
global $con;
$result = mysqli_query($con,"SELECT * FROM demos");
if(!$result)
{
die("Invalid query ".mysqli_error($con));
}
return $result;
}
get_demos();
By adding global $con.