探讨php define()函数及defined()函数使用详解
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,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 ($)
设置常量时,不需要在前面加上“$”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
define(name,value,case_insensitive)
Parameter 参数 |
Description 描述 |
---|---|
name | Required. Specifies the name of the constant 必要参数。指定常量的名称 |
value | Required. Specifies the value of the constant 必要参数。指定常量的值 |
case_insensitive | Optional. Specifies whether the constant name should be case-insensitive. If set to TRUE, the constant will be case-insensitive. Default is FALSE (case-sensitive) 可选参数。指定常量的名称是否是不区分大小写的[case-insensitive]。如果设置为True,则不区分字母大小写;如果设置为False,则区分字母大小写。默认值是:False |
Example 1
案例1
Define a case-sensitive constant:
指定一个常量(区分大小写):
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:
Hello you! How are you today?
Example 2
案例2
Define a case-insensitive constant:
指定一个常量(不区分大小写):
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:
Hello you! How are you today?
The defined() function checks whether a constant exists.
defined()函数的作用是:检查一个常量是否存在。
Returns TRUE if the constant exists, or FALSE otherwise.
如果该常量存在,则返回True;如果不存在,则返回False。
Syntax
语法
复制代码 代码如下:
defined(name)
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:
1

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