Call to a member function validate() on a non-object using own library

That's not what the manual says!

PHP Code:

$CI =& get_instance();

$CI->load->helper('url');
$CI->load->library('session');
$CI->config->item('base_url');
etc. 


I am talking about pure PHP nothing related to CI..

Here is working example of your first post class

PHP Code:

class Generate_token  
{
    public function __construct()
        {
            $this->CI =& get_instance();
        }
      
    public function generate()
        {
            $raw_random_bytes = mcrypt_create_iv(6, MCRYPT_DEV_URANDOM);
            $encoded_random_bytes = base64_encode($raw_random_bytes);
            $token = strtr(trim($encoded_random_bytes, '='), array('+' => '-', '/' => '_'));
            if($this->validate($token)==$token)
                {
                    return true;
                }
        }
    public function validate($token)
        {
            $sql = "SELECT id FROM url_tokens WHERE short_url = ?";
            $query = $this->CI->db->query($sql, array($token));
            if($query->num_rows==0)
                {
                    return $token;
                }
            else
                {
                    $this->generate();
                }    
        }    
} 


When you are in Class you can call methods from the same class using $this->methodname()
When you are in class and want to call method from some class loaded with CI you can use $this->CI->classs->method name() but first inside class constructor you have to set $this->CI to get instance of CI..

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