在发布上获取自定义post类型元

我正在研究以下代码。为什么发布帖子时无法获得”自定义帖子”元信息？我尝试了这个：

function get_cpt_meta($post_ID) {
 $post = get_post($post_ID);
 $meta = get_post_custom(); 
         $mfname = $meta['f_name'][0];
         $mlname = $meta['l_name'][0];
         echo $mfname. " " . $mlname;
}
add_action('publish_book', 'get_cpt_meta');

和

function get_cpt_meta($post_ID) {
 $post = get_post($post_ID);
 $meta = get_post_custom($post); 
         $mfname = $meta['f_name'][0];
         $mlname = $meta['l_name'][0];
         echo $mfname. " " . $mlname;
}
add_action('publish_book', 'get_cpt_meta');

#1

请看以下内容：

function get_cpt_meta($post_id){
  $f_name = get_post_meta($post_id, 'f_name');
  $l_name = get_post_meta($post_id, 'l_name');
  echo $mfname. " " . $mlname;      
}
add_action('save_post', 'get_cpt_meta', 11, 1);