Code Igniter（类stdClass的对象无法转换为字符串）erro

this is my model:

function Countosweb(){
    $sql="SELECT count(*) FROM `os` WHERE `status`='PENDIENTE ASIGNAR TÉCNICO'";
    return $this->db->query($sql)->row();
}

this is my controller:

public function indexp() {
    if((!$this->session->userdata('session_id')) || (!$this->session->userdata('logado'))){
        redirect('mapos/login');
    }
    $this->data['ordensW'] = $this->mapos_model->getOsWeb();
    $this->data['osn']= $this->mapos_model->Countosweb($sql);
    $this->data['ordens'] = $this->mapos_model->getOsAbertas();
    $this->data['produtos'] = $this->mapos_model->getProdutosMinimo();
    $this->data['os'] = $this->mapos_model->getOsEstatisticas();
    $this->data['estatisticas_financeiro'] = $this->mapos_model->getEstatisticasFinanceiro();
    $this->data['menuPainel'] = 'Painel';
    $this->data['view'] = 'mapos/panel';
    //$this->session->set_flashdata('success','mensaje de prueba');
    $this->load->view('tema/alte',$this->data);

}

and this is my view:

<a href="#" class="dropdown-toggle" data-toggle="dropdown">
                <i class="fa fa-bell-o"></i>
                <?php
                if($osn != null){echo '<span class="label label-warning">'.$osn.'</span>';} // this is the line which is occasinating the problem.
                ?>
           </a>

so i got this error:

A PHP ERROR WAS ENCOUNTERED

Severity: 4096

Message: Object of class stdClass could not be converted to string

Filename:tema/alte.php

line Number: 67

Please help to find the problem

PD: excuse me, my english is not very good

thanks all for helping me, i solved it:

i changed this:

<a href="#" class="dropdown-toggle" data-toggle="dropdown">
            <i class="fa fa-bell-o"></i>
            <?php
            if($osn != null){echo '<span class="label label-warning">'.$osn.'</span>';} // this is the line which is occasinating the problem.
            ?>   
</a>

For this:

<a href="#" class="dropdown-toggle" data-toggle="dropdown">
                <i class="fa fa-bell-o"></i>
                <?php
                if($osn != null){
                  foreach($osn as $on){echo'<span class="label label-warning">'.$on.'</span>';} 
                }
                ?>
</a>

you shouldn't use echo to print Object - the return value in ordinary case is object or arrayuse :

 print_r($osn) ; 

to see the output then loop through it or use object [$object_name->item]

I advice you change your function to this as to get the number of rows returned.

function Countosweb(){
    $sql="SELECT * FROM `os` WHERE `status`='PENDIENTE ASIGNAR TÉCNICO'";
    return $this->db->query($sql)->num_rows();
}

Then your html should look like this.

<a href="#" 
   class="dropdown-toggle" 
   data-toggle="dropdown">

   <i class="fa fa-bell-o"></i>
   <?php
       if(isset($osn)){
           echo '<span class="label label-warning">'.$osn.'</span>';
       } // this is the line which is occasinating the problem.
   ?>
</a>