defined

constant

Last updated: Fri, 20 Nov 2009

define

(PHP 4, PHP 5)

define — Defines a named constant

Opis

bool define ( string $name , mixed $value [, bool $case_insensitive = false ] )

Defines a named constant at runtime.

Parametry

name: The name of the constant.
value: The value of the constant; only scalar and null values are allowed. Scalar values are integer, float, string or boolean values. It is possible to define resource constants, however it is not recommended and may cause unpredictable behavior.
case_insensitive: If set to TRUE, the constant will be defined case-insensitive. The default behavior is case-sensitive; i.e. CONSTANT and Constant represent different values.

Zwracane wartości

Zwraca TRUE w przypadku powodzenia, FALSE w przypadku błędu.

Przykłady

Przykład #1 Defining Constants


<?php
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.

define("GREETING", "Hello you.", true);
echo GREETING; // outputs "Hello you."
echo Greeting; // outputs "Hello you."

?>

Zobacz też:

defined() - Checks whether a given named constant exists
constant() - Returns the value of a constant
The section on Constants

defined

constant

Last updated: Fri, 20 Nov 2009

add a note User Contributed Notes
define

bohwaz.net
16-Aug-2009 12:54


Note that define don't care at all about the constant name, you can give everything as a constant name, even if the PHP documentation says that the allowed characters are [a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*



Just try this :



<?php define('anything::()$', 'test'); ?>



You won't be able to access this constant though, it will throw a parse error, either through constant() or define(), but if you do that :



<?php print_r(get_defined_constants()); ?>



You will see that the constant is registered at the end of the array. Yes that's totally useless. But you can try other things that will work with constant() :



<?php define('...', 'test'); echo constant('...'); ?>



Will echo 'test'. Yeah that's a pretty strange behavior.



And please note that defining object constants outside of objets don't work :



<?php

class myObject { }

define('myObject::CONSTANT', 'test');

?>

Anonymous
20-Jul-2009 05:31


My notice to: redeclare define -  it is possible



php -v



--> PHP 5.2.6-3ubuntu4.1 with Suhosin-Patch 0.9.6.2

Zend Engine v2.2.0, Copyright (c) 1998-2008 Zend Technologies

php -r "define('TEST','foo',true);

var_dump(TEST);

define('TEST','bar');

var_dump(TEST);"



string(3) "foo"

string(3) "bar"



greetings

sixd at php dot net
17-Jul-2009 09:24


A note on redefining:



Constants can't be redefined:



$ php -r "define('A', 1); var_dump('A'); define('A', 2); var_dump('A');";

string(1) "A"

PHP Notice:  Constant A already defined in Command line code on line 1

string(1) "A"



But using the case insensitive setting shows that the internal

representation is lower case:



$ php -r "define('A', 1, true); var_dump('A'); define('A', 2); var_dump('A');";

string(1) "A"

string(1) "A"



Note the lower case 'a' in the second define() here:

$ php -r "define('A', 1, true); var_dump('A'); define('a', 2); var_dump('A');"; 

string(1) "A"

PHP Notice:  Constant a already defined in Command line code on line 1

string(1) "A"

danbettles at yahoo dot co dot uk
14-Apr-2009 06:56


define() will define constants exactly as specified.  So, if you want to define a constant in a namespace, you will need to specify the namespace in your call to define(), even if you're calling define() from within a namespace.  The following examples will make it clear.



The following code will define the constant "MESSAGE" in the global namespace (i.e. "\MESSAGE").



<?php

namespace test;

define('MESSAGE', 'Hello world!');

?>



The following code will define two constants in the "test" namespace.



<?php

namespace test;

define('test\HELLO', 'Hello world!');

define(__NAMESPACE__ . '\GOODBYE', 'Goodbye cruel world!');

?>

Aldonio
27-Mar-2009 04:24


This code will define every key of an array, and if its a multidimentional array it will define it as parent_child1_child2_etc.



<?php

function define_array( $array, $keys = NULL )

{

    foreach( $array as $key => $value )

    {

        $keyname = ($keys ? $keys . "_" : "") . $key;

        if( is_array( $array[$key] ) )

            define_array( $array[$key], $keyname );

        else

            define( $keyname, $value );

    }

}

?>

ceo at l-i-e dot com
11-Mar-2009 10:04


In PHP 4.4.9, you cannot use certain names for constants.





Specifically, reserved words such as 'PRINT', 'IF', etc.





Oddly enough, you get different behaviour for some:





<?php


define('IF', 42);


echo "IF: ", IF, "<hr />\n";


?>





yields PHP Parse error:  syntax error, unexpected T_IF





<?php


define('PRINT', 13);


echo "PRINT: ", PRINT, "<hr />\n";


?>





yields PHP Parse error:  syntax error, unexpected ')'





Not sure if this is still true in PHP 5 or not, but it's worth noting if it is.

Anonymous
09-Mar-2009 09:03


With php 5.30 it is possible to make some "restrictions", in case u use namespaces...

The following function allows only uppercase and, if 3 param isset, gives E_USER_ERROR instead of E_NOTICE:



<?php

namespace bla;



function define($c,$v,$x=false) {

    $c = strtoupper($c);

    if (!defined($c)) {

        // not to use \define here, as the syntax highlighting does not work correctly here...

        return define($c, $v, true);

    } else if ($x == true) {

        trigger_error('setting constant "'.$c.'" is not allowed', E_USER_ERROR);

    }

    return null;

}



define('PHP_VERSION', '1');

define('PHP_VERSION', '1') || trigger_error('constant already defined', E_USER_NOTICE);

define('PHP_VERSION', '1', true);

?>

jv at vip dot ie
09-Mar-2009 12:14


Probably the most efficient way of creating a constant array is to put it in a function like this:





<?php


function my_const_arr()


{


   return array


   (


      'key1' => 'val 1',


      'key2' => 'va' 2


   );


}


?>





Then use at will like so...


<?php $my_const_arr = my_const_arr(); ?>

usuroer dot king at hotmail dot co dot uk
08-Mar-2009 12:15


Referring to "This-Is-A-Test" constant below.



When echoing it the script thinks you performing a series of minus (subtraction) thus since THIS and IS, A, TEST are not defined they are 0 by default. So 0-0-0-0 = 0.



As explained that a hyphen cannot be used within a variable.

downwind at web dot de
02-Feb-2009 04:48


I'm reffering to the note below by mittiprovence.



The described behavior has nothing to do with the fact that there is a constant in the condition.



Comparing a non-numeric string to the integer 0 by using == will return true, since the string will be casted to integer - which will be zero. If your string starts with a number, it will be castet to an integer with the number as value.



To avoid the described behavior, you should use === instead of ==.



Finally, the behavior discribed by mittiprovence is exacly the expected behavior as defined in the manual.



For further information read the manual:



http://www.php.net/manual/en/types.comparisons.php



http://www.php.net/manual/en/language.operators.comparison.php



http://www.php.net/manual/en/language.types.string.php #language.types.string.conversion



<?php



if (0 == "some string") { // is true

echo "0 == 'some string'";

}



if (1 == "some string") { // is false

echo "1 == 'some string'";

}



if (1 == "1 some string") { // is true

echo "1 == '1 some string'";

}



if (0 === "some string") { // is false

echo "0 === 'some string'";

}



?>

eparkerii at carolina dot rr dot com
22-Oct-2008 07:01


Found something interesting.  The following define:





<?php


define("THIS-IS-A-TEST","This is a test");


echo THIS-IS-A-TEST;


?>





Will return a '0'.





Whereas this:





<?php


define("THIS_IS_A_TEST","This is a test");


echo THIS_IS_A_TEST;


?>





Will return 'This is a test'.





This may be common knowledge but I only found out a few minutes ago.





[EDIT BY danbrown AT php DOT net: The original poster is referring to the hyphens versus underscores.  Hyphens do not work in defines or variables, which is expected behavior.]

pistachio
01-Sep-2008 11:41


A better solution to that of thscheer at web dot de, is to simply serialize the array.



for example:



<?php



$fruits = array("apple", "banana", "orange");



define("FRUITS", serialize($fruits));



// Now to use it

$my_fruits = unserialize(FRUITS);



?>



As you can see this is a much simpler and more efficient way to stuff arrays into constants.

jan at webfontein dot nl
27-Jul-2008 12:20


For translating with variables and define, take also a look on the constant() function.



Example : 



<?php 

define('PAYMENT_IDEAL',"iDEAL Payment ( NL only )");

define('PAYMENT_MASTERCARD',"Mastercard Payment ( international )");



$payparam='MASTERCARD';



echo constant("PAYMENT_$payparam");



// output : 

// Mastercard Payment ( international )

?>

thscheer at web dot de
20-Jun-2008 09:18


How to define an array as constant with define?



there is a simple way to define an array of values as constant...



just 



define ("constant-name","value1,value2,value3,value4");



$t_array = preg_split('/,/', constant(constant-name), -1, PREG_SPLIT_NO_EMPTY);



var_dump($t_array);



array(4) { [0]=> string(6) "value1" [1]=> string(6) "value2" [2]=> string(6) "value3" [3]=> string(6) "value4" } 



Now you can iterate over the array defined as constant ...

ceo at l-i-e dot com
05-May-2008 03:30


I'm not sure if it's version dependent, but apparently this works:

define('APPLICATION_NOW', time());



This can be quite handy for time-dependent code...



You can then do:

class foo {

  $private now = APPLICATION_NOW;

}



and have a consistent time-stamp across the application, which is nice.



Works for me in 5.2.5



I didn't think it worked before...

jason@sitehatchery dot com
25-Apr-2008 06:28


You can store your constant as the value of a variable like this:



$variable=VARIABLE;



To access the constant, do this:  constant($variable).



Beware: if your variable changes, then you loose your reference to the constant - but the constant itself will not change.



I've found this especially useful for storing the constant string   (i.e. VARIABLE) in a database.

rayro at gmx dot de
15-Sep-2007 09:53


just a note to the previous post by e s lin d sey at g mail dot co m:



Well as u said, it is not the best workaround. To resolve this "Problem" without getting incredible loss of performance, you are able to make the use of "variable functions" like "variable variables":



<?php

$def = 'constant';

$string = <<<END

    This is PHP running on<br />

    {$def('PHP_OS')}

END;

var_dump($string);

?>



In this example we make use of the "constant" function which is builtin, and it will output:



string(37) " This is PHP running on

WINNT"



Tested on PHP 5...

Best regards

e s lin d sey at g mail dot co m
13-Aug-2007 08:38


Constants can't be referenced from within quotes or (more importantly IMHO) from within HEREDOC syntax. This is a huge drawback in my opinion. Here's two of my workarounds:



<?php



//PHP5 only -- more efficient

$constarray = get_defined_constants(true);

foreach($constarray['user'] as $key => $val)

    eval(sprintf('$_CONSTANTS[\'%s\'] = \'%s\';', addslashes($key), addslashes($val)));



//PHP4+ -- less efficient because it defines (potentially) hundreds of unnecessary constants

foreach(get_defined_constants() as $key => $val)

    eval(sprintf('$_CONSTANTS[\'%s\'] = \'%s\';', addslashes($key), addslashes($val)));



?>



Now you can refer to your defined constants using the $_CONSTANTS array. Note that because this is NOT a superglobal, a few caveats apply:



<?php



//run code snippet here to define $_CONSTANTS in global scope...



$mv = $_CONSTANTS['FOO']; //works



function my_function1()

{

    $mv = $_CONSTANTS['BAR']; //doesn't work! not defined!

}



function my_function2()

{

    global $_CONSTANTS;

    $mv = $_CONSTANTS['BAR']; //ah, this works!

}



?>



I realize this is not ideal, either for performance or for convenience of being able to refer to constants without regard to scope, but it is a workaround that works. Depending on your application, it may be easier to shift your paradigm a bit and use the following method instead, declaring your constants as variables first:



<?php



//first, define our constants...

$_CONSTANTS['FOO'] = 'bar';

$_CONSTANTS['BAR'] = 'foo';



//now, turn them into real constants...

foreach($_CONSTANTS as $key => $val)

    define($key, $val);



//now, you can use either format to refer to a constant

print($_CONSTANTS['FOO']);   //prints 'bar'

print(FOO);                  //prints 'bar'

print("$_CONSTANTS['FOO']"); //prints 'bar'

                             //prints 'blah bar blah'

print <<<EOF

  blah {$_CONSTANTS['FOO']} blah

EOF;



?>



Hope this helps some of you out there, I know being able to utilize my constants in HEREDOC helped me a ton!

smifffy at smith-net dot org dot uk
25-Jul-2007 11:23


a basic function to auto assign a numeric value that increase by itself each time - used in some permission style scripts



<?php

function define_bitwise($constant_name, $reset = False)

{

    static $bitwise_next = 1;



    if ( $reset === True )

    {

        $bitwise_next = 1;

    }



    define($constant_name, $bitwise_next);

        

    $bitwise_next += $bitwise_next;

}

?>



when reset it set to True, resets that value to 1 and starts afresh

creeves at dja dot com
19-Jul-2007 01:59


Intersting to note:



I found this in php5 on windows 



If you try to unset a constant (which you cant but maybe you have a Jr. programmer or something).  The error message that is thrown is:



<?php

define ("SOME_CONSTANT", true);

unset (SOME_CONSTANT);

?>



Parse error: parse error, unexpected ')', expecting T_PAAMAYIM_NEKUDOTAYIM

nl-x at bita dot nl
09-Jul-2007 05:34


Watch out. You can define a new constant with the name NULL with define("NULL","FOO");. But you must use the function constant("NULL"); to get it's value. NULL without the function call to the constant() function will still retrieve the special type NULL value.

Within a class there is no problem, as const NULL="Foo"; will be accessible as myClass::NULL.

stangelanda at arrowquick dot com
01-Jan-2007 02:59


An improvement on the function from bobbykjack at yahoo dot co dot uk on the concept by richard dot quadling at bandvulc dot co dot uk:

<?php

function adefine($constant_name, $value=null) {

    static $increment = 0; // 1 for bitmask



    if (is_null($value)) {

        define($constant_name, ++$increment); // $increment=$increment<<1 for bitmask

    } else {

        define($constant_name, $value);

        if (is_numeric($value)) {

            $increment = $value;

        }

    }

}

?>

If you pass it a second argument it defines it normally, and resets the increment if the value is numeric.  This way the function can replace define, and you can reset the counter for a new set of constants.

<?php

adefine ('RULE_CALLBACK_FORMAT', 1); // 1

adefine ('RULE_CHANGE_CALLBACK_ON_ERROR'); // 2

adefine ('RULE_CHANGE_COMPARE_DATE'); // 3

adefine('KEYWORD', 'hodgepodge'); // hodgepodge <-- defined normally

adefine ('RULE_CHANGE_ON_DATE'); // 4



adefine ('ERROR_DESC', 1); // 1 <-- Counter reset

adefine ('ERROR_EXPECTED_RESULT'); // 2

?>

12-Feb-2005 04:45


Better pack with define() for all who really miss Java package management:



Use this "manifest.php" on very first script start or copy it to your config.somehow.php.



<?php

$__packages = array(

    "org.ilove.java.more",

    "org.ilove.python.too",

    "net.php.isok"

);



define("C_IS_WINDOWS", false);

define("C_DIR", (C_IS_WINDOWS ? "\\" : "/"));

define("C_PATH_ROOT", str_replace("/", C_DIR, $_SERVER["DOCUMENT_ROOT"]).C_DIR);

define("C_PATH_CORE", C_PATH_ROOT."core".C_DIR);

define("C_PATH_CLASS", C_PATH_CORE."classes".C_DIR);

define("C_APPLICATION_BASE", C_PATH_CORE.C_DIR."application".C_DIR);



$total_packages = 0;

$i = sizeof($__packages);

while($i-- > 0) {

    $tokens = explode(".", $__packages[$i]);

    $j = sizeof($tokens);

    while($j-- > 0) {

        $token = strtolower(trim($tokens[$j]));

        if(strlen($token) > 0 && !defined($token)) {

            define($token, ($j == 0 ? C_PATH_CLASS : "").$tokens[$j].C_DIR);

            $total_packages++;

        }

    }

}

define("C_PACKAGE_COUNT", $total_packages);

?>



With restrictions on non-package constants, you now can call your files like that:



<?php



require_once org.ilove.java.more."Than.php";



?>



Regards

Robi

phpnet at trenkner dot de
14-Mar-2003 11:59


---[Editor's Note]---


As of PHP 5.0.0 this is possible. You can define class-only constants, which can be called like Foo::Constant1 from the outside


---[End Note]---





Please keep in mind that 





class AClass {


  define ("Const1", "Value1");


  ... }





didn't work. You have to make all your constant definitions before you open the class. So





define ("Const1", "Value1");


class AClass {


  ... }





would be correct.

radovan dot biciste at managestar dot com
07-Nov-2001 04:45


Wonder how to work with variable which name is stored in a constant? 


Here it is:


<?php


define("VAR_NAME","test");


// assigning value


${VAR_NAME} = "value";


// getting value back


echo ${VAR_NAME};


?>

ste at opk dot no
29-Aug-2001 05:41


To use a constant to show an element of an array inside a string:


define ('C', 0); print ("element 0: {$a[C]}");


The { & } around the variable signals that what's inside should be treated as a variable and not a string.


Note that 'print ("a constant:{C}");' wont work as ZERO is a constant.

add a note

defined

constant

Last updated: Fri, 20 Nov 2009