add_post_meta($post_id, $meta_key, $meta_value,$unique);

//为ID为1的文章添加_postviews自定义字段，值为99
add_post_meta(1, "_postviews", "99");
var_dump(get_post_meta(1));echo"<br />";
//为ID为1的文章添加_postviews自定义字段，值为999，并允许重复自定义字段名称
add_post_meta(1, "_postviews", 999,false);
var_dump(get_post_meta(1));echo"<br />";

array(1) {
 ["_postviews"]=>
 array(1) {
  [0]=>
  string(2) "99"
 }
}

array(1) {
 ["_postviews"]=>
 array(2) {
  [0]=>
  string(2) "99"
  [1]=>
  string(3) "999"
 }
}


//不允许重复自定义字段的代码
add_post_meta(1, "_postviews", "996",true);
var_dump(get_post_meta(1));echo"<br />";
add_post_meta(1, "_postviews", "997",true);
var_dump(get_post_meta(1));echo"<br />";
array(1) {
 ["_postviews"]=>
 array(1) {
  [0]=>
  string(3) "996"
 }
}


array(1) {
 ["_postviews"]=>
 array(1) {
  [0]=>
  string(3) "996"
 }
}

<?php
 add_meta_box( $id, $title, $callback, $post_type, $context, $priority, $callback_args );
 ?>

function add_xz_box (){//添加设置区域的函数
add_meta_box('xz_box_1', 'add_meta_box 测试', 'xz_box_1','post','side','high',array('str1','str2'));
};
//在'add_meta_boxes'挂载 add_xz_box 函数
add_action('add_meta_boxes','add_xz_box');
 
 
function xz_box_1($post,$boxargs){//显示设置区域的回调函数
 echo"add_meta_box 测试";
};