The define() function defines a constant.
define()函數的作用是：定義一個常量。
Constants are much like variables, except for the following differences:
常量[constant]與變量[variable]有很多相似的地方，因此，很容易混淆；下面，我們列舉一下常量[constant]與變量[variable]之間的不同點：
•A constant's value cannot be changed after it is set
一個常量值在指定之后就不可以更改；
•Constant names do not need a leading dollar sign ($)
設置常量時，不需要在前面加上“$”符號；
•Constants can be accessed regardless of scope
常量可以被所有范圍的域訪問；
•Constant values can only be strings and numbers
常量的值只能是“字符串[string]”和“數字[number]”；
Syntax
語法
define(name,value,case_insensitive)
|
Parameter |
Description |
|---|---|
|
name |
Required. Specifies the name of the constant |
|
value |
Required. Specifies the value of the constant |
|
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) |
Example 1
案例1
Define a case-sensitive constant:
指定一個常量（區分大小寫）：
<?phpdefine("GREETING","Hello you! How are you today?");echo constant("GREETING");?>
The output of the code above will be:
上述代碼將輸出下面的結果：
Hello you! How are you today?
Example 2
案例2
Define a case-insensitive constant:
指定一個常量（不區分大小寫）：
<?phpdefine("GREETING","Hello you! How are you today?",TRUE);echo constant("greeting");?>
The output of the code above will be:
上述代碼將輸出下面的結果：
Hello you! How are you today?
The defined() function checks whether a constant exists.
defined()函數的作用是：檢查一個常量是否存在。
Returns TRUE if the constant exists, or FALSE otherwise.
如果該常量存在，則返回True；如果不存在，則返回False。
Syntax
語法
defined(name)
|
Parameter |
Description |
|---|---|
|
name |
Required. Specifies the name of the constant to check |
Example
案例
<?phpdefine("GREETING","Hello you! How are you today?");echo defined("GREETING");?>
The output of the code above will be:
上述代碼將輸出下面的結果：
1
