Документация PHP
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defined
(PHP 4, PHP 5)
defined — Checks whether a given named constant exists
Описание
bool defined ( string $name )
Checks whether the given constant exists and is defined.
Замечание: 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().
Список параметров
- name
-
The constant name.
Возвращаемые значения
Returns TRUE if the named constant given by name has been defined, FALSE otherwise.
Примеры
Пример #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;
}
?>
Смотрите также
- define()
- constant()
- get_defined_constants()
- function_exists()
- The section on Constants