How to handle issues in log-in?

[eluser]miwrath[/eluser]
Hey guys, this is my problem on my project about logging-in...

the problem is if i input 'correct' username & password...it can log in...nothings wrong...
BUT if i input my username & my password with a blank space...it can log in.

Now the thing is, I want this issue to solve...that users cannot log-in without using exact
data they have to input...i want to solve the spaces issue...

Please help me with this one...

I appreciate positive responses from all of the members...(:

this is my user_model code:

Code:

function User_model()
    {
        parent::Model();
    }
    
    function check_login($username, $password)
    {
        //login_checker
      
              
        $query_str = "SELECT * FROM users WHERE username = ? and password = ?";
        
        $result = $this->db->query($query_str, array($username, $password));
        
          
       if ($result->num_rows() == 1)
        {    

           return $result->row(0)->teach_id;
        }
        else
        {
            return false;
        }
      
        
    }

this is my controller codes:

Code:

function login()
        {
            $this->load->helper('security');
            $this->form_validation->set_rules('username', 'Username', 'trim|required|max_length[30]|alpha_numeric|xss_clean');  
            $this->form_validation->set_rules('password', 'Password', 'trim|required|max_length[10]|alpha_numeric|xss_clean');  
                                
                    
            if ($this->form_validation->run() == FALSE)
            {
                $this->load->view('view_registrar');
            }
            else
            {
               // echo 'You are great!';
                //process the input and login the user;
                
                $username = $_POST['username'];
                $username = $this->input->post('username');
                $password = $_POST['password'];
                $password = $this->input->post('password');
                
               //extract($_POST);
            
               $teach_id = $this->User_model->check_login($username, $password);
              
               if (! $teach_id)
               {
                   //login failed error
                  
                   $this->session->set_flashdata('login_error', TRUE);
                  
                   redirect('index.php');
               }
               else
               {
                   //login

                   $this->session->set_userdata(array(
                                           'logged_in' => TRUE,
                                           'teach_id' => $teach_id
                                                     ));
                  
                   redirect('index.php/registrar/main_page');
                  
               }