php常量 define() constant() , defined()
define——定义常量,若定义true，则读取时不区分大小写bool define( string name, mixed value [, bool case_insensitive])
常量只能包含标量数据（boolean，integer，float和 string）。
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.
define("GREETING", "Hello you.", true);
echo GREETING; // outputs "Hello you."
echo Greeting; // outputs "Hello you."
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constant()——读取常量
mixed constant( string name)
define("MAXSIZE", 100);
echo MAXSIZE;
echo constant("MAXSIZE"); // same thing as the previous line
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defined——判断常量是否定义
bool defined( string name)
if (defined('CONSTANT')) {
echo CONSTANT;
}
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预定义常量
__FILE__ 取得文件的物理地址 注：左右各2条下划线
echo __FILE__ //C:\wamp\www\T1\1.php
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