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.");
echoCONSTANT;// outputs "Hello world."
echoConstant;// outputs "Constant" and issues a notice.

define("GREETING","Hello you.",true);
echoGREETING;// outputs "Hello you."
echoGreeting;// outputs "Hello you."

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constant()――读取常量

mixedconstant( string name)

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define("MAXSIZE",100);

echoMAXSIZE;
echoconstant("MAXSIZE");// same thing as the previous line

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defined――判断常量是否定义

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booldefined( string name)

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if (defined('CONSTANT')) {
????echoCONSTANT;
}

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预定义常量

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__FILE__?? 取得文件的物理地址?注：左右各2条下划线

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echo __FILE__??? //C:\wamp\www\T1\1.php

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