defined

(PHP 4, PHP 5, PHP 7)
Checks whether a given named constant exists
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().

Parameters:
name

The constant name.

Returns:

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

Examples:
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;
}
?>

See also:

define() -

constant() -

get_defined_constants() -

function_exists() -

Constants -

doc_php
2016-02-24 16:06:11
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