Magic constants in PHP – Learn in details with the examples

What are Magic constants in PHP?

The Magic constants in PHP are predefined constants that start and end with double underscores (__), with capital letters, and whose values change as per their use in a program.

These constants are called magic constants as their value changes where they will be used.
There are nine Magic constants in PHP. Let’s see them one by one.

1. __LINE__

The __LINE__ magic constant will give you the current line number where it is used in a program.

Example:

<?php
 echo "This is line no ".__LINE__;
 echo "<br>This is line no ".__LINE__;
 echo "<br>This is line no ".__LINE__;
?>

Output:

This is line no 2
This is line no 3
This is line no 4

 

2. __FILE__

The __FILE__ magic constant will give the full path and the current file name where it is used.

<?php
 echo "<h3>__FILE__ Example:</h3>";
 
 echo "The path of this file is = ".__FILE__;
?>

Output:

__FILE__ Example:
The path of this file is = C:xampphtdocsphpclassoopmagicconstantsfile.php

 

3. __DIR__

The __DIR__ magic constant will give you a full directory path the file where it is used. This constant will not show trailing slash in the path unless it is a root directory of a file.

Example:

<?php
 echo "<h3>__DIR__ Example:</h3>";
 
 echo "The path of this file is = ".__DIR__;
?>

Output:

__DIR__ Example:
The path of this file is = C:xampphtdocsphpclassoopmagicconstants

 

4. __FUNCTION__

The __FUNCTION__  will give you the function name where it is used. It will work only inside the function, outside the function, it will return a blank value.

Example:

<?php
 echo "<h3>__FUNCTION__ Example:</h3>";
 
 function showName()
 {
  //__FUNCTION__ inside a function
  echo "The name of this function is ".__FUNCTION__;
 }
 
 showName();
 
 //__FUNCTION__ outside a function
 echo "<br>The name of this functio is ".__FUNCTION__;
 
?>

Output:

__FUNCTION__ Example:
The name of this function is showName
The name of this functio is

 

5. __CLASS__

The __CLASS__ magic constant will you the name of a current class where it is used. It is one of the important Magic constants in PHP. This is one of the most used Magic constants in PHP.

Example:

<?php
 echo "<h3>__CLASS__ Example:</h3>";
 
 class Test
 {
  function showName()
  {
   echo "The name of a class is = ".__CLASS__;
  }
 }
 
 $test = new Test;
 $test->showName();
?>

Output:

__CLASS__ Example:
The name of a class is = Test

 

6. __TRAIT__

The __TRAIT__ magic constant will give you the current trait name where it is used.

<?php
 echo "<h3>__TRAIT__ Example:</h3>";
 
 Trait testTrait
 {
  function showName()
  {
   echo "The name of a trait is = ".__TRAIT__;
  }
 }
 class Test
 {
  use testTrait;
 }
 
 $test = new Test;
 $test->showName();
?>

Output:

__TRAIT__ Example:
The name of a trait is = testTrait

 

7. __METHOD__

__METHOD__ is another one in Magic constants in PHP. The __METHOD__ constant will return the name of a class method where it is used. It will also show the name of a class with a scope resolution operator.

Example:

<?php
 echo "<h3>__METHOD__  Example:</h3>";
 
 class Test
 {
  function showName()
  {
   echo "The name of a method is = ".__METHOD__;
  }
 }
 
 $test = new Test;
 $test->showName();
?>

Output:

__METHOD__  Example:
The name of a method is = Test::showName

 

8. __NAMESPACE__

The __NAMESPACE__ constant will return the current namespace of a file where it is used.

Example:

<?php
 namespace TestNamespace;
 echo "<h3>__NAMESPACE__  Example:</h3>";
 
 class Test
 {
  function showName()
  {
   echo "The name of a method is = ".__NAMESPACE__;
  }
 }
 
 $test = new Test;
 $test->showName();
?>

Output:

__NAMESPACE__  Example:
The name of a method is = TestNamespace

 

9. ClassName::class

The ClassName::class will you the fully qualified name of a class. It is particularly useful with the namespaced classes. Here “ClassName” can be any class with which you want to use it.

Example:

<?php
 echo "<h3>ClassName::class Example:</h3>";
 
 namespace TestNamespace 
 {
  class ClassTest
  {
  
  }
    
  echo ClassTest::class;
 }
?>

Output:

TestNamespaceClassTest

In this tutorial, you have seen the Magic constants in PHP with examples.

In the next tutorial, you will learn about PHP Anonymous functions in detail.