i want to save checkboxes values in entity reference checkboxes field with node_save :
   $form['wrapperrr']['id_offre'] = array(         '#title' => t('Liste des Offres'),         '#type' => 'checkboxes',         '#options' => $optionsoffres,      ); 
and into the submit button :
$node->field_entity_reference['und'][]['value'] =$form_state['values']['wrapperrr']['id_offre'];