function log_validation()
{
$this->form_validation->set_rules('username', '用户名', 'required');
$this->form_validation->set_rules('password', '密码', 'required');
$this->form_validation->set_message('required', "%s 不能为空!");
if($this->form_validation->run() === FALSE)//若输入错误则继续停留在登录界面
{
$this->load->view('log/login');
}
else
{//输入成功则继续判断是否是有效的用户
...
}