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後就不可以更改;
•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
復制代碼 代碼如下:
define(name,value,case_insensitive)
Example 1
案例1
Define a case-sensitive constant:
指定一個常量(區分大小寫):
復制代碼 代碼如下:
<?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:
復制代碼 代碼如下:
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):
復制代碼 代碼如下:
<?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:
復制代碼 代碼如下:
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
復制代碼 代碼如下:
defined(name)
Example
案例
復制代碼 代碼如下:
<?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:
復制代碼 代碼如下:
1