PHP self-study no00013 constant definition value to determine whether it has been defined

<!--常量定义define(常量名，常量值,true)true表示常量名大小写一样-->
<!--取值有二种，一种直接赋值，另一种用函数constant(常量名)动态获取常量值-->
<!--函数defined(常量名)判定常量是否已定义-->
<?php error_reporting(E_ALL ^ E_NOTICE); //忽略错误
	define("zhaowanshi","myname我的名字");
	echo zhaowanshi;
	echo &#39;<br />';
	echo ZHAOWANSHI;
	echo '<br>';
	
	define("taizhou","浙江台州是我所在的地方",true);
	echo taizhou;
	echo '<br>';
	echo TAIZHOU;
	echo '<br>';
	
	$name = "TAIZHOU";
	echo constant($name);
	echo '<br>';
	echo defined("TAIZHOU");
?>