


In-depth explanation of the php define() function and the usage of the defined() function_PHP Tutorial
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
Case 1
Define a case-sensitive constant:
Specify a constant (case-sensitive):
The output of the code above will be:
The above code will output the following results:
Hello you! How are you today?
Example 2
Case 2
Define a case-insensitive constant:
Specify a constant (case-insensitive):
The output of the code above will be:
The above code will output the following result:
Hello you! How are you today?
The defined() function checks whether a constant exists. The function of the defined() function is to check whether a constant exists.
Returns TRUE if the constant exists, or FALSE otherwise.
If the constant exists, it returns True; if it does not exist, it returns False.
Syntax
Syntax
Parameter Parameter |
Description
|
||||
---|---|---|---|---|---|
name | Required. Specifies the name of the constant to checkRequired parameter. Specify the name of the constant object |
Example
Case
The output of the code above will be:
The above code will output the following result:
1

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