user logout

<nav class="navbar navbar-default">
  <div class="container-fluid">
    <!-- Brand and toggle get grouped for better mobile display -->
    <div class="navbar-header">
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
        <span class="sr-only">Toggle navigation</span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </button>

      <?=anchor (base_url(),'Alfatihmart', ['class'=> 'navbar-brand'])?>
    </div>

    <!-- Collect the nav links, forms, and other content for toggling -->
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
      <?php if($this->session->userdata('username')) :?>
      <ul class="nav navbar-nav navbar-right">
       <li>
          <?php echo 'You Are:' .$this->session->userdata('username') ;?>
        </li>
      </ul>
        <li>
          <?php echo anchor('logout', 'Logout');?>
        </li>
      </ul>
    <?php endif; ?>
    </div><!-- /.navbar-collapse -->
  </div><!-- /.container-fluid -->
</nav>