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 'TEST' is the name of a constant named TEST */
if (defined('TEST')) {
    echo TEST;
}
?>

Смотрите также

define() - Defines a named constant
constant() - Returns the value of a constant
get_defined_constants() - Returns an associative array with the names of all the constants and their values
function_exists() - Возвращает TRUE, если данная функция определена
The section on Constants