defined
(PHP 4, PHP 5)
defined — Checks whether a given named constant exists
说明
bool defined
( string $name
)
Checks whether the given constant exists and is defined.
Note: If you want to see if a variable exists, use isset() as defined() only applies to constants. If you want to see if a function exists, use function_exists().
参数
- name
-
The constant name.
返回值
Returns TRUE if the named constant given by name has been defined, FALSE otherwise.
范例
Example#1 Checking Constants
<?php
/* Note the use of quotes, this is important. This example is checking
* if the string 'CONSTANT' is the name of a constant named CONSTANT */
if (defined('CONSTANT')) {
echo CONSTANT;
}
?>
CDN