define
Определяет именованную константу во время выполнения.
Список параметров
Замечание:
Возможно определить константы с помощью функции define() зарезервированными или даже некорректными именами, значения которых могут быть (только) получены через функцию constant() . Однако, делать это не рекомендуется.
Значение константы. В PHP 5 value должно быть скалярным значением ( int , float , string , bool или null ). В PHP 7 также возможно использовать тип array .
Хотя возможно определить константы с типом resource , не рекомендуется это делать, поскольку может привести к непредсказуемому поведению.
Если параметр установлен как true , то константа будет определена без учёта регистра. По умолчанию константа чувствительна к регистру, то есть CONSTANT и Constant представляют разные значения.
Начиная с PHP 7.3.0, определение нечувствительных к регистру констант объявлено устаревшим. Начиная с PHP 8.0.0, допустимым значением является только false , передача true вызовет предупреждение.
Замечание:
Нечувствительные к регистру константы хранятся в нижнем регистре.
Возвращаемые значения
Возвращает true в случае успешного выполнения или false в случае возникновения ошибки.
Список изменений
| Версия | Описание |
|---|---|
| 8.0.0 | Передача true в case_insensitive теперь выдаёт ошибку уровня E_WARNING . Передача false всё ещё разрешена. |
| 7.3.0 | Параметр case_insensitive объявлен устаревшим и будет удалён в версии 8.0.0. |
| 7.0.0 | Допустимы значения типа array . |
Примеры
Пример #1 Определение констант
define ( «CONSTANT» , «Hello world.» );
echo CONSTANT ; // выводит «Hello world.»
echo Constant ; // выводит «Constant» и выдаёт уведомление.
define ( «GREETING» , «Hello you.» , true );
echo GREETING ; // выводит «Hello you.»
echo Greeting ; // выводит «Hello you.»
// Начиная с PHP 7
define ( ‘ANIMALS’ , array(
‘собака’ ,
‘кошка’ ,
‘птица’
));
echo ANIMALS [ 1 ]; // выводит «кошка»
Пример #2 Определение констант зарезервированными именами
Этот пример демонстрирует возможность определения константы с тем же именем, что и магическая константа. Поскольку это, очевидно, сбивающее с толку поведение, не рекомендуется делать это на практике.
var_dump ( defined ( ‘__LINE__’ ));
var_dump ( define ( ‘__LINE__’ , ‘test’ ));
var_dump ( constant ( ‘__LINE__’ ));
var_dump ( __LINE__ );
?>
Результат выполнения данного примера:
bool(false) bool(true) string(4) "test" int(5)
Смотрите также
- defined() — Проверяет существование указанной именованной константы
- constant() — Возвращает значение константы
- Смотрите раздел Константы
User Contributed Notes 17 notes
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:
define ( ‘ENABLE_UPLOADS’ , true );
?>
Since I wanted to remove the ability for uploads, I changed the file to read:
//define(‘ENABLE_UPLOADS’, true);
?>
However, to my surprise, the program was still allowing uploads. Digging deeper into the code, I discovered this:
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.
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».)
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»).
namespace test ;
define ( ‘MESSAGE’ , ‘Hello world!’ );
?>
The following code will define two constants in the «test» namespace.
namespace test ;
define ( ‘test\HELLO’ , ‘Hello world!’ );
define ( __NAMESPACE__ . ‘\GOODBYE’ , ‘Goodbye cruel world!’ );
?>
With php 7 you can now define arrays.
consider the following code:
define ( «EXPLENATIVES» , [ 1 => «Foo Bar» , 2 => «Fehw Bahr» , 3 => «Foo Bahr» , 4 => «Fooh Bar» , 5 => «Fooh Bhar» , 6 => «Foo Barr» , 7 => «Foogh Bar» , 8 => «Fehw Barr» , 9 => «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
Love this new implementation !
The value of a constant can be the value of another constant.
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
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:
define ( «VEG» , «cabbage» );
require( «another file» );
define ( «FRUIT» , «apple» );
// «another file»:
echo VEG ; // cabbage
echo FRUIT ; // FRUIT
?>
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.
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 ( $this , true );
>
Found something interesting. The following define:
define ( «THIS-IS-A-TEST» , «This is a test» );
echo THIS — IS — A — TEST ;
?>
Will return a ‘0’.
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.]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).
# 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 «
» ;
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.
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»
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 );
$serialized = DEFINEANARRAY; // passing directly the defined will not work
$our_array = unserialize($serialized);
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).
// «echo CONST» prints 1, same as «echo const», «echo CoNst», etc.
define ( ‘CONST’ , 1 , true );
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.
For translating with variables and define, take also a look on the constant() function.
define ( ‘PAYMENT_IDEAL’ , «iDEAL Payment ( NL only )» );
define ( ‘PAYMENT_MASTERCARD’ , «Mastercard Payment ( international )» );
echo constant ( «PAYMENT_ $payparam » );
// output :
// Mastercard Payment ( international )
?>
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:
define ( ‘GOOD_OCTAL’ , 0700 );
define ( ‘BAD_OCTAL’ , 0800);
print GOOD_OCTAL ;
print ‘
‘ ;
print BAD_OCTAL ;
?>
Result:
448
0
writing the constant name without the quotation-marks (as mentioned in the notes) throws an E_NOTICE and should be avoided!
define ( TEST , ‘Throws an E_NOTICE’ );
?>
Result:
Notice: Use of undefined constant TEST — assumed ‘TEST’
It may be worth stating that a define function must be executed before its global constant is referenced.
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».
A namespace constant can be defined using the define function, the constant defined this way is not global.
namespace WuXiancheng ;
\ define ( ‘China\Sichuan\Guangan\Yuechi\ZIP’ , 638300 );
echo ZIP ; //Use of undefined constant ZIP
echo \ China \ Sichuan \ Guangan \ Yuechi \ ZIP ; // 638300
?>
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:
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
- Разные функции
- connection_aborted
- connection_status
- constant
- define
- defined
- die
- eval
- exit
- get_browser
- __halt_compiler
- highlight_file
- highlight_string
- hrtime
- ignore_user_abort
- pack
- php_strip_whitespace
- sapi_windows_cp_conv
- sapi_windows_cp_get
- sapi_windows_cp_is_utf8
- sapi_windows_cp_set
- sapi_windows_generate_ctrl_event
- sapi_windows_set_ctrl_handler
- sapi_windows_vt100_support
- show_source
- sleep
- sys_getloadavg
- time_nanosleep
- time_sleep_until
- uniqid
- unpack
- usleep