defined()

(PHP 4, PHP 5, PHP 7)

检查某个名称的常量是否存在

说明

检查该名称的常量是否已定义。

如果你要检查一个变量是否存在，请使用isset()。defined()函数仅对constants有效。如果你要检测某个函数是否存在，使用function_exists()。

参数

常量的名称。

返回值

如果名称$name的常量已定义，返回TRUE；未定义则返回FALSE。

范例

检查常量

参见

• define()定义一个常量
• constant()返回一个常量的值
• get_defined_constants()返回所有常量的关联数组，键是常量名，值是常量值
• function_exists()如果给定的函数已经被定义就返回 TRUE
• 章节Constants

My preferred way of checking if a constant is set, and if it isn't - setting it (could be used to set defaults in a file, where the user has already had the opportunity to set their own values in another.)

Dan.

You can use the late static command "static::" withing defined as well. This example outputs - as expected - "int (2)"

Dont forget to put the name of your constant into single quotation mark. You will not get an error or a warning.