define

(PHP 4, PHP 5)

define — Defines a named constant

Описание

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

Defines a named constant at runtime.

Список параметров

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.

case_insensitive

If set to TRUE, the constant will be defined case-insensitive. The default behaviour is case-sensitive; i.e. CONSTANT and Constant represent different values.

Возвращаемые значения

Возвращает TRUE в случае успешного завершения или FALSE в случае возникновения ошибки.

Примеры

Пример #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."

?>

Смотрите также

Коментарии

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 )
?>
2008-07-27 08:20:05
http://php5.kiev.ua/manual/ru/function.define.html
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.]
2008-10-22 15:01:16
http://php5.kiev.ua/manual/ru/function.define.html
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!');
?>
2009-04-14 14:56:37
http://php5.kiev.ua/manual/ru/function.define.html
The value of a constant can be the value of another constant.

<?php

define
("NEW_GOOD_NAME_CONSTANT""I have a value");
define("OLD_BAD_NAME_CONSTANT"NEW_GOOD_NAME_CONSTANT);

echo 
NEW_GOOD_NAME_CONSTANT// current
echo OLD_BAD_NAME_CONSTANT// legacy

?>
2010-03-25 21:15:19
http://php5.kiev.ua/manual/ru/function.define.html
Автор:
This is obvious, but easy to forget: if you include a file, the include file can only make use of constants already defined. For example:

<?php
define
("VEG","cabbage");
require(
"another file");
define("FRUIT","apple");

// "another file":
echo VEG// cabbage
echo FRUIT// FRUIT
?>
2011-03-01 15:24:13
http://php5.kiev.ua/manual/ru/function.define.html
To clear up a few thing:
Integers with 0 in front work. But since PHP (and many other languages) handle them as octal values, they're only allowed a range of 0-7:

<?php
 define
('GOOD_OCTAL'0700);
 
define('BAD_OCTAL'0800);

 print 
GOOD_OCTAL;
 print 
'<br>';
 print 
BAD_OCTAL;
?>

Result:
448
0

---------------------------------------

Furthermore, 

writing the constant name without the quotation-marks (as mentioned in the notes) throws an E_NOTICE and should be avoided!

<?php
 define
(TEST'Throws an E_NOTICE');
?>

Result:
Notice: Use of undefined constant TEST - assumed 'TEST'
2011-07-06 04:32:03
http://php5.kiev.ua/manual/ru/function.define.html
Be aware that if "Notice"-level error reporting is turned off, then trying to use a constant as a variable will result in it being interpreted as a string, if it has not been defined.

I was working on a program which included a config file which contained:

<?php
define
('ENABLE_UPLOADS'true);
?>

Since I wanted to remove the ability for uploads, I changed the file to read:

<?php
//define('ENABLE_UPLOADS', true);
?>

However, to my surprise, the program was still allowing uploads. Digging deeper into the code, I discovered this:

<?php
if ( ENABLE_UPLOADS ):
?>

Since 'ENABLE_UPLOADS' was not defined as a constant, PHP was interpreting its use as a string constant, which of course evaluates as True.
2015-02-22 05:11:45
http://php5.kiev.ua/manual/ru/function.define.html
I think worth mentioning is that define() appears to ignore invalid constant names.
One immediate implication of this seem to be that if you use an invalid constant name you have to use constant() to access it and obviously that you can't use the return value from define() to tell you whether the constant name used is invalid or not.

For example:
$name = '7(/!§%';
var_dump(define($name, "hello")); // outputs bool(true)
var_dump(constant($name)); // outputs string(5) "hello"
2016-02-13 13:35:38
http://php5.kiev.ua/manual/ru/function.define.html
Php 7 - Define: "Defines a named constant at runtime. In PHP 7, array values are also accepted."

But prior PHP 7, you can maybe do this, to pass an array elsewhere using define:

$to_define_array = serialize($array);
define( "DEFINEANARRAY", $to_define_array );

... and so ...

$serialized = DEFINEANARRAY; // passing directly the defined will not work
      $our_array = unserialize($serialized); 

print_r($our_array);
2016-09-05 23:46:51
http://php5.kiev.ua/manual/ru/function.define.html
Автор:
There's an undocumented side-effect of setting the third parameter to true (case-insensitive constants): these constants can actually be "redefined" as case-sensitive, unless it's all lowercase (which you shouldn't define anyway).

The fact is that case-sensitive constants are stored as is, while case-insensitive constants are stored in lowercase, internally. You're still allowed to define other constants with the same name but capitalized differently (except for all lowercase).

<?php
 
// "echo CONST" prints 1, same as "echo const", "echo CoNst", etc.
 
define('CONST'1true);
  echo CONST; 
// Prints 1

 
define('CONST'2);
  echo CONST; 
// Prints 2
 
echo CoNsT; // Prints 1
 
echo const; // Prints 1

  // ** PHP NOTICE: Constant const already defined ** 
 
define('const'3);
  echo const; 
// Prints 1
 
echo CONST; // Prints 2
?>

Why would you use this?

A third party plugin might attempt to define a constant for which you already set a value. If it's fine for them to set the new value, assuming you cannot edit the plugin, you could define your constant case-insensitive. You can still access the original value, if needed, by using any capitalization other than the one the plugin uses. As a matter of fact, I can't think of another case where you would want a case-insensitive constant...
2017-04-15 23:33:44
http://php5.kiev.ua/manual/ru/function.define.html
Автор:
With php 7 you can now define arrays. 

consider the following code:
<?php

define
"EXPLENATIVES", [=> "Foo Bar"=> "Fehw Bahr"=> "Foo Bahr"=> "Fooh Bar"=> "Fooh Bhar"=> "Foo Barr"=> "Foogh Bar"=> "Fehw Barr"=> "Fu bar"10 => "Foo Bahr"11 => "Phoo Bar"12 => "Foo Bawr"13 => "Phooh Baughr"14 => "Foogan Bargan"15 => "Foo Bahre"16 => "Fu Bahar"17 => "Fugh Bar"18 => "Phou Baughr"]);

//set up define methods using mixed values; both array and non-array values
define("NAVBTNS", [EXPLENATIVES"Nouns""Verbs""Adjectives"]);

//function to create a dropdown menu using the EXPLENATIVES array $btn=EXPLENATIVES=assoc_array

function construct_navbar_buttons(){
   
   
$btns '<ul class="nav navbar-nav">';
                       
    foreach(
NAVBTNS as $button => $btn){
        if(
is_array($btn)){
           
$btns .= '<li class="dropdown">
                        <a class="dropdown-toggle" data-toggle="dropdown" href="?id='
.$btn.'">
                            <i class="glyphicon glyphicon-user"></i> You Dare Say? <i class="glyphicon glyphicon-collapse-down"></i>
                        </a>
                        <ul class="dropdown-menu dropdown-user">'
;
            foreach(
EXPLENATIVES as $key => $button){
               
$btns .= '<li><a href="#">'.$button.'</a></li>';
            }
           
$btns .= '</ul>';
        }else{   
           
$btns .= '<li><a href="#">'.$btn.'</a></li>';
        }
    }
   
   
$btns .= '</ul>';
    return 
$btns;
}           

Love this new implementation!

?>
2017-04-16 12:45:53
http://php5.kiev.ua/manual/ru/function.define.html
Not sure why the docs omit this, but when attempting to define() a constant that has already been defined, it will fail, trigger an E_NOTICE and the constant's value will remain as it was originally defined (with the new value ignored).

(Guess that's why they're called "constants".)
2017-06-08 06:10:58
http://php5.kiev.ua/manual/ru/function.define.html
You can define constants with variable names (works also with constant values or variables or array values or class properties and so on - as long it's a valid constant name).

<?php
   
   
# Define a constant and set a valid constant name as string value
   
define("SOME_CONSTANT""NEW_CONSTANT");
   
   
# Define a second constant with dynamic name (the value from SOME_CONSTANT)
   
define(SOME_CONSTANT"Some value");
   
   
# Output
   
echo SOME_CONSTANT// prints "NEW_CONSTANT"
   
echo "<br>";
    echo 
NEW_CONSTANT// prints "Some value"
   
   
?>

Needless to say that you'll lose your IDE support for refactoring and highlighting completely for such cases.
No clue why someone would / could actually use this but i thought it's worth mentioning.
2018-09-18 12:29:56
http://php5.kiev.ua/manual/ru/function.define.html
Автор:
It may be worth stating that a define function must be executed before its global constant is referenced.

Example:

Abc();
define("TEST", 23);
function Abc()
    {
    echo TEST;
    } // Abc

This code fails with a Notice-level message. TEST is treated here as being the string "TEST".
2019-07-19 18:03:39
http://php5.kiev.ua/manual/ru/function.define.html
A namespace constant can be defined using the define function, the constant defined this way is not global.

<?php
   
namespace WuXiancheng;
   
\define('China\Sichuan\Guangan\Yuechi\ZIP'638300);
    echo 
ZIP//Use of undefined constant ZIP
   
echo \China\Sichuan\Guangan\Yuechi\ZIP// 638300
?>
2020-03-22 02:34:27
http://php5.kiev.ua/manual/ru/function.define.html
If you happen to name your constant the same as a function name (either a built-in function or a user-defined one), PHP can handle this correctly based on context. For example:

<?php
function myfunc() {
   return 
'function output';
}

define('MYFUNC''constant value');

// note that function names are NOT case-sensitive
// so calling MYFUNC() is the same as calling myfunc()

echo 'MYFUNC(): ' MYFUNC() . ', MYFUNC: ' MYFUNC;
?>

Output:
MYFUNC(): function output, MYFUNC: constant value
2021-10-06 23:05:21
http://php5.kiev.ua/manual/ru/function.define.html
Since version 8 or 8.1, beat me if I recall any type of class 
as defined constant value is perfectly valid. 

Should You use it, I wouldn't know. 
Most probably, referencing with such instances will fail badly. 
But it might come handy for public and readonly classes. 

<?php

  define 
('ClassInstance'
  new class extends 
\My\OtherClass {
   
    private 
bool $toggle false;
    private 
float $real 1.2345;
    private ?
string $obj null;
   
    public function 
__construct() {
       
$this-> privatemethod();
    }

    private function 
privatemethod() {
       
$this-> obj var_export ($thistrue);   
    }   
 
  });

?>
2023-04-30 03:33:49
http://php5.kiev.ua/manual/ru/function.define.html

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