$expression = $this->input->get('search');
$posts_count = $this->Posts_model->search_count($expression);
// set it to page so pagination know which value to update
$query_string_segment = 'page';

// in case it\'s disabled
$config['enable_query_strings'] = TRUE;

// Setting this config to TRUE will add existing query string arguments back into the URL after the URI segment and before the suffix
$config[‘reuse_query_string’] = TRUE;

$this->_initPagination("/posts/search", $posts_count, $query_string_segment);