PHP: Magic constants

Magic constants

Magic constants are keywords that are replaced with information about their own location in the source code: their file and line, and the function, class, trait, namespace, or property hook enclosing them. Despite their name, they are not actual constants: defined() and constant() do not recognize them, and a constant of the same name created with define() does not affect them. They are case-insensitive. When used outside of the relevant context (e.g. __CLASS__ outside of a class), they are replaced with an empty string.

**PHP's magic constants**
Name	Description
`__LINE__`	The line number on which it is written.
`__FILE__`	The full path and filename of the file in which it is written, with symlinks resolved.
`__DIR__`	The directory of the file, equivalent to `dirname(__FILE__)`. It has no trailing slash unless it is the root directory.
`__FUNCTION__`	The name of the function in which it is written, including its namespace (e.g. `Foo\bar`). Inside a method, only the method name. For anonymous functions, a name generated by the engine that includes where the closure was defined (as of PHP 8.4.0; previously `{closure}`).
`__CLASS__`	The name of the class in which it is written, including its namespace (e.g. `Foo\Bar`). Inside a trait, the name of the class using the trait. For anonymous classes, a name generated by the engine. To get the name of the class a method was called on, use `static::class`.
`__TRAIT__`	The trait name, including its namespace (e.g. `Foo\Bar`).
`__METHOD__`	The class and method name of the method in which it is written (e.g. `Foo\Bar::baz`). Inside a trait, the trait name is used instead of the class name. Outside of a method, the same as `__FUNCTION__`.
`__PROPERTY__`	The name of the property, when used inside a property hook. Available as of PHP 8.4.0.
`__NAMESPACE__`	The name of the current namespace.

Example #1 Using magic constants

<?php
namespace App;

function helper()
{
    echo __FUNCTION__, "\n";
    echo __METHOD__, "\n";
}

trait Greets
{
    public function greet()
    {
        echo __CLASS__, "\n";
        echo __TRAIT__, "\n";
        echo __METHOD__, "\n";
        echo __FUNCTION__, "\n";
    }
}

class Greeter
{
    use Greets;
}

helper();
(new Greeter)->greet();
echo __NAMESPACE__, "\n";

The above example will output:

App\helper
App\helper
App\Greeter
App\Greets
App\Greets::greet
greet
App

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User Contributed Notes 5 notes

down

theking2 at king dot ma ¶

4 years ago

If PHP is run inside a web server request there is an important difference between the __DIR__ constant and $_SERVER['DOCUMENT_ROOT'].

Where __DIR__ of a PHP script contained within a sub-folder will include the complete server path $_SERVER['DOCUMENT_ROOT'] will contain a server path up to the _root_ of the application. This can be helpful when for instance an auto-loader is defined in an include file sitting inside a sub-folder and where the classes are located in another folder at the root of the application.

down

webmaster at event-horizon dot lt ¶

6 months ago

I have got this script:
<?=
$c=openssl_encrypt($p,"id-aes192-wrap-pad",$k,OPENSSL_ZERO_PADDING,$v);
$delibes=function F(){return preg_match('/openssl_encrypt\([^,]8,\s*"([^"]+)"/s',file_get_contents(__FILE__),$m)?$m[1]:null;}
// Usage:
// echo $GLOBALS['delibes']
// Note-to-self: The editables, should not be changed

I have no idea how to change __FILE__, perhaps using __DIR__."but what is the relative path?"

down

Athralon dot media at gmail dot com ¶

6 months ago

This is a magic constant: "but what is the relative path?"

down

dirk at biztechwiz dot com ¶

6 months ago

Getting the magic constants from the right place is important.  For example, creating a function to log location information requires explicit inclusion.

<?php
/***********
* magic_constants_include.php
*
* Magic constant test include file
*/
function showInclude($file=__FILE__, $lineno=__LINE__) {
    echo "Parameter values: $file ($lineno)\n";
    echo "Local constants: " . __FILE__ . "; " . __LINE__ . "\n";
}
?>

<?php
/************
* magic_constants_test.php
*/

require_once 'magic_constants_include.php';

echo "Function call with parameter defaults:\n";
showInclude();

echo "Function call with parameter explicit magic constants:\n";
showInclude(__FILE__, __LINE__);
?>

Results:
php -f magic_constants_test.php
Function call with parameter defaults:
Parameter values: /home/dirk/project/dirk/php/magic_constants_include.php (7)
Local constants: /home/dirk/project/dirk/php/magic_constants_include.php; 9
Function call with parameter explicit magic constants:
Parameter values: /home/dirk/project/dirk/php/magic_constants_test.php (12)
Local constants: /home/dirk/project/dirk/php/magic_constants_include.php; 9

down

-2

chris at ocproducts dot com ¶

3 years ago

Note that __CLASS__ and __METHOD__ both reference the class the code is written in, not whatever the object class is. E.g. if you have an object of class B inheriting from class A, any usage of __CLASS__ in class A is going to give "A".

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Magic constants

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User Contributed Notes 5 notes