php 상수 선언 - define

define에 의해서 선언된 값은 상수로 변경이 불가능하며(상수니까)

$로 변수 식별자 없이 바로 사용이 가능하다.

<?php   define ('YEAR',  3000);   echo YEAR; ?>

[링크 : http://php.net/manual/kr/language.constants.php]

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Performance results

Test performed	Time spent	Memory consumed
Using define()	100%	32.6%
Using class constants	30.2%	100%
Using apc_define_constants()	24.2%	32.0%
Using hidef	13.9%	13.5% (*)

(*) hidef consumes memory during initialization, but this was not taken into account for this test

[링크 : http://shwup.blogspot.com/2010/04/about-constants.html]

    [링크 : http://stackoverflow.com/questions/148185/how-efficient-is-define-in-php]