PHP Magic constants

PHP Magic Constants are some predefined constants you can say, which provide some special features to the PHP language. These can be used by embedding with echo(), and each of these provide a special kind of information which a programmer may need.

These are called Magic Constant because unlike regular constants Magic Constants doesn,t always give the same value,i.e., they would have different values for different scenarios. For example, a Magic Constant which returns the line number on which it has been used, will give different values for different lines.

These Magic Constants are case-insensitive, so no problem with any case. Always remember that Magic Constants starts and end with double underscore (__). Now below are given some Magic Constants with proper explanation and examples, it will help you to understand it very easily. Please continue reading.

LINE

The __LINE__ magic constant returns the line number on which it has been used. For example, if you use it on first line it will return 1, on 3rd line it will return 3 and so on. Take a look at the example below to understand how you can use it with echo().

Example

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

Output

Line number 2
Line number 3
Line number 4

FILE

The __FILE__ magic constant returns the exact path of the file in which it is used in combination with echo() but if you use it with include() then it will return the filename of the file which is included. Take a look at the example below to understand it properly.

Example

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

FUNCTION

The __FUNCTION__ magic constant returns the name of the function inside which it is been used. It is a case sensitive constant so it will return the function name in the exact case in which it is written. Earlier in PHP 4, it used to return the function name in lowercase which was later changed in PHP 5.

Example

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

Output

The function name is - myFunction

CLASS

The __CLASS__ magic constant works same as __FUNCTION__,but it returns class name. It is also case sensitive so it will return the name of the class in the exact same case in which it was declared. See the example.

Example

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

Output

MyClass

METHOD

The __METHOD__ magic constant return the name of the method inside which it has been used. It is also case sensitive so it will return the name same as it was declared.

Example

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

Output

Sample::myMethod

DIR

The __DIR__ magic constant returns the directory of the file. If used inside an include, the directory of the included file is returned.

Example

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

NAMESPACE

The __NAMESPACE__ magic constant returns the name of the current namespace.

Example

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

Output

MyNamespace

trait

The __trait__ magic constant return the trait name where this magic constant is included. Take a look at the example below to understand how it work.

Example

<?php trait CodeRepublics{ function cr(){ echo __trait__; } } class Company{ use CodeRepublics; } $a = new Company; $a->cr(); ?>

Output

CodeRepublics

Differences between constants and variables are:

Constant's value cannot be changed once defined, but variable's value can be changed.
The '$' sign is not used in Constants but it is mandatory in Variables.
Constants need the define() function to get created but the variables can be defined by using simple assignment.
Constants are Global by default but not Variables.

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