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深入php define()函数以及defined()函数的用法详解

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Release: 2016-06-06 20:31:03
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本篇文章是对php中的define()函数以及defined()函数的用法进行了详细的分析介绍,需要的朋友参考下

The define() function defines a constant.
define()函数的作用是:定义一个常量。
Constants are much like variables, except for the following differences:
常量[constant]与变量[variable]有很多相似的地方,因此,很容易混淆;下面,虚拟主机,我们列举一下常量[constant]与变量[variable]之间的不同点:

•A constant's value cannot be changed after it is set
一个常量值在指定之后就不可以更改;
•Constant names do not need a leading dollar sign ($)
设置常量时,服务器空间,不需要在前面加上“$”符号;
•Constants can be accessed regardless of scope
常量可以被所有范围的域访问;
•Constant values can only be strings and numbers
常量的值只能是“字符串[string]”和“数字[number]”;

Syntax
语法

复制代码 代码如下:


define(name,value,case_insensitive)


Parameter
参数 Description
描述

name Required. Specifies the name of the constant to check
必要参数。指定常量对象的名称

Example
案例

复制代码 代码如下:




The output of the code above will be:
上述代码将输出下面的结果:

复制代码 代码如下:


1

,虚拟主机
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