PHP: define - Manual

Description

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

Defines a named constant. See the section on constants for more details.

The name of the constant is given by name; the value is given by value.

The optional third parameter case_insensitive is also available. If the value TRUE is given, then the constant will be defined case-insensitive. The default behaviour is case-sensitive; i.e. CONSTANT and Constant represent different values.

Example 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." ?>

Returns TRUE on success or FALSE on failure.

See also defined(), constant() and the section on Constants.

User Contributed Notes
define

dsan at pml dot ac dot uk
08-Apr-2005 10:17


Just to clarify what 'david at nospam webgroup dot org' said:

${} is actually the syntax for 'variable variables'.

So in this specific case:

Starting with the line:

${MY_CONST} = serialize(array('foo' => 'bar'));

PHP will expand the constant and use it as the name of the variable:

$test = serialize(array('foo' => 'bar'));



So in fact there is no assignment to a constant (which would defy the definition of 'constant') but instead an assignment to a variable named by the _value_ of the constant.

david at nospam webgroup dot org
31-Mar-2005 05:14


To the comment posted by Raphael Crawford Marks:



You're actually manipulating the variable $test.  The value of a constant obviously cannot be changed after it is set: hence the term constant.  Try setting $test to something first, then running your code.  It *WILL* be clobbered.

Raphael Crawford-Marks
10-Mar-2005 01:28


Notes on using serialize to store an array in a constant:



<?php

define('MYCONST','test'); //define constant with junk value

${MYCONST} = serialize(array("foo" => "bar")); //change value to serialized array

echo "constant: ".${MYCONST};

echo "<br>";

$unserialized = unserialize(${MYCONST}); //unserialize

echo "unserialized: ".$unserialized['foo'];

?>



Note that you have to use ${} around the constant name for this to work.

11-Feb-2005 10:45


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

tech at litigationdataservices dot com
25-Jan-2005 03:05


If your oft-used array is already defined, but the key value doesn't start at ['0'], --for example if you need an array of state names conforming to GIS codes, it's far easier to define the array in a low-level class and call it by 



$classname->states[$STATEID];



than it is to try to define it as a constant or use an function to call it later from a free-standing array. It's also useful to do it this way when all you want to do is recall a fixed array value, but don't necessarily want to hit the database just to get it.

technopasta at yahoo dot com dot au
02-Jan-2005 07:55


You can't use arrays in constants, so I came up with this two line function to get around it.



<?php



function const_array($constant) {

  $array = explode(",",$constant);

  return $array;

                         };

?>



So now if you define a constant like



<? define('myconstant','item1,item2,item3') ?>



and then use my function



<? $myarray = const_array(myconstant); ?>



$myarray will now contain an array with 

item1

item2

item3



Hope this is useful for someone...

konstantin #at schukraft #dot org
22-Sep-2003 05:13


Constants MUST evaluate to scalar values only.

You are encouraged to use serialize/unserlialize

to store/retrieve an array in a constant:



define('CONST',serialize(array('a','b','foo'=>'bar')));

var_dump(CONST);

var_dump(unserialize(CONST));

phpnet at trenkner dot de
14-Mar-2003 05:59


---[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
06-Nov-2001 10:45


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 12:41


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.