PHP features nine predefined constants known as "magic constants" because their values vary depending on where they are used.
These magic constants are denoted by a double underscore at the beginning and end, with the exception of the ClassName::class constant.
Magic Constants
Below are the magic constants along with description and examples:
__CLASS__: If used inside a class, the class name is returned.
<?php
class Car {
public function getClassName() {
return __CLASS__;
}
}
$audi = new Car();
echo $audi->getClassName();
?>
/*
Output:
Car
*/__DIR__: The directory of the current file is returned.
<?php
echo __DIR__;
?>
/*
Output:
C:/phpscripts/test-scripts
*/__FILE__: The current file name including the full path is returned.
<?php
echo __FILE__;
?>
/*
Output:
C:/phpscripts/test-scripts/file.php
*/ __FUNCTION__: If used inside a function, the function name is returned.
<?php
function getFunctionName() {
return __FUNCTION__;
}
echo getFunctionName();
?>
/*
Output:
getFunctionName
*/__LINE__: The current line number is returned.
<?php
echo __LINE__;
?>
/*
Output:
2
*/__METHOD__: If used inside a function that belongs to a class, both class and function name are returned.
<?php
class Car {
public function getMethodName() {
return __METHOD__;
}
}
$honda = new Car();
echo $honda->getMethodName();
?>
/*
Output:
Car::getMethodName
*/__NAMESPACE__: If used inside a namespace, the name of the namespace is returned.
<?php
namespace MyNamespace;
function getNamespaceName() {
return __NAMESPACE__;
}
echo getNamespaceName();
?>
/*
Output:
MyNamespace
*/__TRAIT__: If used inside a trait, the trait name is returned.
<?php
trait MessageTrait {
public function displayTraitName() {
echo __TRAIT__;
}
}
class Greeting {
use MessageTrait;
}
$instance = new Greeting();
$instance->displayTraitName();
?>
/*
Output:
MessageTrait
*/ClassName::class: Returns the name of the specified class and the name of the namespace, if any.
<?php
namespace MyNamespace;
class Car {
public function getClassName() {
return self::class;
}
}
$Mersadise = new Car();
echo $Mersadise->getClassName();
?>
/*
Output:
MyNamespace\Car
*/