PHP : Seven most important, most practical and most useful PHP Magic Constants

• __FILE__ – The full path and filename of the file.
• __DIR__ – The directory of the file.
• __FUNCTION__ – The function name.
• __CLASS__ – The class name.
• __METHOD__ – The class method name.
• __LINE__ – The current line number of the file.
• __NAMESPACE__ – The name of the current namespace

<?php

 // Set namespace (works only with PHP 5.3)
 namespace TestProject;

 // This prints file full path and name
 echo "This file full path and file name is '" . __FILE__ . "'.\n";

 // This prints file full path, without file name
 echo "This file full path is '" . __DIR__ . "'.\n";

 // This prints current line number on file
 echo "This is line number " . __LINE__ . ".\n";

 // Really simple basic test function
 function test_function_magic_constant() {
  echo "This is from '" . __FUNCTION__ . "' function.\n";
 }

 // Prints function and used namespace
 test_function_magic_constant();

 // Really simple class for testing magic constants
 class TestMagicConstants {
  // Prints class name
  public function printClassName() {
   echo "This is " . __CLASS__ . " class.\n";
  }

  // Prints class and method name
  public function printMethodName() {
   echo "This is " . __METHOD__ . " method.\n";
  }

  // Prints function name
  public function printFunction() {
   echo "This is function '" . __FUNCTION__ . "' inside class.\n";
  }

  // Prints namespace name (works only with PHP 5.3)
  public function printNamespace() {
   echo "Namespace name is '" . __NAMESPACE__ . "'.\n";
  }
 }

 // Create new TestMagicConstants class
 $test_magic_constants = new TestMagicConstants;

 // This prints class name and used namespace
 $test_magic_constants->printClassName();

 // This prints method name and used namespace
 $test_magic_constants->printMethodName();

 // This prints function name inside class and used namespace
 // same as method name, but without class
 $test_magic_constants->printFunction();

 // This prints namespace name (works only with PHP 5.3)
 $test_magic_constants->printNamespace();

?>

This file full path and file name is '/tmp/magic_constants/magic.php'.
This file full path is '/tmp/magic_constants'.
This is line number 13.
This is from 'TestProject\test_function_magic_constant' function.
This is TestProject\TestMagicConstants class.
This is TestProject\TestMagicConstants::printMethodName method.
This is function 'printFunction' inside class.
Namespace name is 'TestProject'.