Cannot modify header

[eluser]fuji2009[/eluser]
Hello i don t understand, i want create an alert just before redirect my page so i try this :

Code:

function desinscrire($event_id){
        $this->load->model('evenement_model');
        $user_login_id = $this->session->userdata('id');
        $this->evenement_model->desinscription_events($user_login_id,$event_id);
        $this->evenement_model->desinscription_valid_events($user_login_id,$event_id);
        echo"[removed]alert('ok')[removed]";
        redirect($_SERVER['HTTP_REFERER']);
    }

but i have this error :

Code:

A PHP Error was encountered
Severity: Warning

Message: Cannot modify header information - headers already sent by (output started at /home/lovemeet/www/siteweb/application/controllers/evenements.php:746)

Filename: helpers/url_helper.php

Line Number: 565

Code:

ligne 746 is : echo"[removed]alert('ok')[removed]";

Why don t work ?


[removed] = < script > without space
Thank you