php: get hostname.php

<?php
function get_host() {
    if ($host = $_SERVER['HTTP_X_FORWARDED_HOST'])
    {
        $elements = explode(',', $host);
        $host = trim(end($elements));
    }
    else
    {
        if (!$host = $_SERVER['HTTP_HOST'])
        {
            if (!$host = $_SERVER['SERVER_NAME'])
            {
                $host = !empty($_SERVER['SERVER_ADDR']) ? $_SERVER['SERVER_ADDR'] : '';
            }
        }
    }
    // Remove port number from host
    $host = preg_replace('/:\d+$/', '', $host);
    return trim($host);
}

I've got an error like this.

I've got an error like this.

Try to var_dump your $_SERVER and look for the variable. However this code is very old, and I wouldn't do it this way nowadays ;)