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'];