require 相对路径如何定位?

[mooowx]

主页的根目录有index.php
/admin/目录下有admin.php
常用的函数: /functions/myfunction.php
数据库类: /class/db.php
函数需用到数据库类

应该如何引用?

方法一(在最初一个文件引用):
index.php
<?php
require "functions/myfunction.php";
require "class/db.php";
?>

admin.php
<?php
require "../functions/myfunction.php";
require "../class/db.php";
?>

方法二(根据需要引用):
index.php
<?php
require "functions/myfunction.php";
?>
myfunction.php
<?php
require "../class/db.php";
?>
//按上面的写法, index.php有误(除非myfunction.php中改成require "class/db.php";),但下面的admin.php却正常,难道其相对路径只与最初执行的PHP脚本有关?
admin.php
<?php
require "../functions/myfunction.php";
?>
请行家指点一二...

[julychina]

require_once ("functions/myfunction.php");
require_once("class/db.php");