Checks whether a given named constant exists

Descrizione

bool defined ( string $name )

Checks whether the given constant exists and is defined.

Nota:
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().

Elenco dei parametri

name: The constant name.

Valori restituiti

Returns TRUE if the named constant given by name has been defined, FALSE otherwise.

Esempi

Example #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;
}
?>

Vedere anche:

define() - Defines a named constant
constant() - Returns the value of a constant
get_defined_constants() - Restituisve un array associativo con i nomi di tutte le costanti ed i loro valori
function_exists() - Return TRUE if the given function has been defined
The section on Constants