超越PHP - Exceed PHP: defined

Description

bool defined ( string name)

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

例子 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; } ?>

注: 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().

See also define(), constant(), get_defined_constants(), function_exists(), and the section on Constants.

add a note User Contributed Notes
defined

Craig at chatspike dot net
01-Dec-2003 03:57

This can be useful if you want to protect pages which get included from
outsiders eyes, on your mail page (the page viewable by people) put
define("X", null); then on all your other pages, you can then do
something like:

if (!defined("X")) {
	echo "You
Cannot Access This Script Directly, Have a Nice
Day.";
	exit();
}

And your page is a good as protected :)

add a note