PHP Magic Constants

In this tutorial, you will learn how to use PHP magic constants.

What are Magic Constants

InPHP ConstantsIn this chapter, we learned how to define and use constants in PHP scripts.

In addition, PHP provides a set of special predefined constants that change according to the position where they are used. These constants are called magic constants. For example, the value of __line__ depends on the line in the script where it is used.

Magic constants start with two underscores and end with two underscores. The following part describes some of the most useful PHP magic constants.

__LINE__

__LINE__ constant returns the current line number of the file, as shown below:

<?php
echo　"Line number　"　.　__LINE__　.　"<br>";　//　Output:　Line number　2
echo　"Line number　"　.　__LINE__　.　"<br>";　//　Output:　Line number　3
echo　"Line number　"　.　__LINE__　.　"<br>";　//　Output:　Line number　4
?>

__FILE__

__FILE__ constant returns the full path and name of the currently executing PHP file. If used inincludeIf used in

<?php
//Show the absolute path of this file
echo　"The full path of this file is:　"　.　__FILE__;
?>

__DIR__

__DIR__ constant returns the directory of the file. If used in include, it returns the directory of the included file. Here is an example:

<?php
//　Show the directory of this file
echo　"The directory of this file is:　"　.　__DIR__;
?>

__FUNCTION__

__FUNCTION__ constant returns the name of the current function.

<?php
function　myFunction(){
　　　　echo　　"The function name is　-　"　.　__FUNCTION__;
}
myFunction();　//　Output:　The function name is　-　myFunction
?>

__CLASS__

__CLASS__ constant returns the currentclassThe name. Here is an instance of:

<?php
class　MyClass
{
　　　　public　function　getClassName(){
　　　　　　　　return　__CLASS__;
　　　　}
}
$obj　=　new　MyClass();
echo　$obj->getClassName();　//　Output:　MyClass
?>

__METHOD__

__METHOD__ constant returns the name of the current class method.

<?php
class　Sample
{
　　　　public　function　myMethod(){
　　　　　　　　echo　__METHOD__;
　　　　}
}
$obj　=　new　Sample();
$obj->myMethod();　//　Output:　Sample::myMethod
?>

__NAMESPACE__

__NAMESPACE__ constant returns the name of the current namespace.

<?php
namespace　MyNamespace;
class　MyClass
{
　　　　public　function　getNamespace(){
　　　　　　　　return　__NAMESPACE__;
　　　　}
}
$obj　=　new　MyClass();
echo　$obj->getNamespace();　//　Output:　MyNamespace
?>