php常量，php常量有哪些
php常量，php常量有哪些
define() 函数用于定义常量。一个常量一旦被定义，就不能再改变或者取消定义。
定义常量的例子：
<?php
define("CONSTANT", "码农教程");
echo CONSTANT;
?>运行
常量名和其它任何 PHP 标签遵循同样的命名规则。合法的常量名以字母或下划线开始，后面跟着任何字母，数字或下划线。
常量默认为大小写敏感，按照惯例常量标识符总是大写的，在脚本执行期间该值不能改变。
定义常量和定义变量的区别：
- 常量前面没有美元符号（$）
- 常量只能用 define() 函数定义，而不能通过赋值语句
- 常量可以不用理会变量范围的规则而在任何地方定义和访问
- 常量一旦定义就不能被重新定义或者取消定义
- 常量的值只能是标量
PHP内置了大量预定义常量，具体可参看PHP手册。
原文地址：http://www.manongjc.com/php/php_constant.html
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