defined

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

Return Values

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

Examples

Example 1353. Checking Constants

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<?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;

}
?>

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Code Examples / Notes » defined

craig

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 :)

ndove

In PHP5, you can actually use defined() to see if an object constant has been defined, like so: <?php class Generic { const WhatAmI = 'Generic'; } if (defined('Generic::WhatAmI')) { echo Generic::WhatAmI; } ?> Thought it may be useful to note. -Nick

joel

If your constants don't show up in your included or required files, then you probably have php safe mode turned on! I ran into this problem, I forgot to turn of safe mode when I was creating a new site.

harald ponce de leon

Beware that some PHP versions return an integer (1 or 0) instead of a boolean. Confirmed PHP versions that return an integer are 4.3.2 and 4.3.4. Relevant bug report: http://bugs.php.net/bug.php?id=27443 This make it impossible to use the following, when the PHP version is not known: if (defined('CONSTANT') === true) { } Relevant commit for PHP 4.3.5 (thanks to Pollita at #php.thinktank): http://cvs.php.net/viewcvs.cgi/Zend/zend_builtin_functions.c? r1=1.124.2.13&r2=1.124.2.14

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connection_aborted
connection_status
connection_timeout
constant
define
defined
die
eval
exit
get_browser
__halt_compiler
highlight_file
highlight_string
ignore_user_abort
pack
php_check_syntax
php_strip_whitespace
show_source
sleep
sys_getloadavg
time_nanosleep
time_sleep_until
uniqid
unpack
usleep