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PHP Magic Constants

PHP provides several predefined constants called Magic Constants that change their values depending on where they are used. These constants start and end with double underscores (__)

Common Magic Constants

<?php
// File path and line information
echo "Current file: " . __FILE__ . "\n";
echo "Current line: " . __LINE__ . "\n";

// Directory information
echo "Directory of the file: " . __DIR__ . "\n";

// Function and class information
function testFunction() {
    echo "Current function: " . __FUNCTION__ . "\n";
}

class TestClass {
    public function testMethod() {
        echo "Current class: " . __CLASS__ . "\n";
        echo "Current method: " . __METHOD__ . "\n";
    }
}

testFunction();
$obj = new TestClass();
$obj->testMethod();
?>

Magic Constants Explained:

  • __LINE__: Current line number of the file
  • __FILE__: Full path and filename of the file
  • __DIR__: Directory of the file
  • __FUNCTION__: Name of the current function
  • __CLASS__: Name of the current class
  • __METHOD__: Name of the current class method
  • __NAMESPACE__: Name of the current namespace
  • __TRAIT__: Name of the current trait

Practical Example

<?php
namespace App\Controllers;

trait LoggerTrait {
    public function log($message) {
        echo "[" . __TRAIT__ . "] " . $message . "\n";
    }
}

class UserController {
    use LoggerTrait;
    
    public function __construct() {
        echo "Namespace: " . __NAMESPACE__ . "\n";
        $this->log("Controller initialized");
    }
}

$controller = new UserController();
?>

Output:

Namespace: App\Controllers
[LoggerTrait] Controller initialized
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