(PHP 4, PHP 5, PHP 7)
defined — 锟斤拷锟侥筹拷锟斤拷锟斤拷频某锟斤拷锟斤拷欠锟斤拷锟斤拷
$name
) : bool锟斤拷锟斤拷锟斤拷锟狡的筹拷锟斤拷锟角凤拷锟窖讹拷锟藉。
Note:
锟斤拷锟斤拷锟揭拷锟斤拷一锟斤拷锟斤拷锟斤拷锟角凤拷锟斤拷冢锟斤拷锟绞癸拷锟� isset()锟斤拷 defined() 锟斤拷锟斤拷锟斤拷锟斤拷 constants 锟斤拷效锟斤拷锟斤拷锟斤拷锟揭拷锟斤拷某锟斤拷锟斤拷锟斤拷锟角凤拷锟斤拷冢锟绞癸拷锟� function_exists()锟斤拷
name锟斤拷锟斤拷锟斤拷锟斤拷锟狡★拷
锟斤拷锟斤拷锟斤拷锟� name 锟侥筹拷锟斤拷锟窖讹拷锟藉，锟斤拷锟斤拷 TRUE锟斤拷未锟斤拷锟斤拷锟津返伙拷 FALSE锟斤拷
Example #1 锟斤拷槌ｏ拷锟�
<?php
/* Note the use of quotes, this is important. This example is checking
* if the string 'TEST' is the name of a constant named TEST */
if (defined('TEST')) {
echo TEST;
}
?>