Magic constants

PHP provides a large number of predefined constants to any script which it runs. Many of these constants, however, are created by various extensions, and will only be present when those extensions are available, either via dynamic loading or because they have been compiled in.

There are nine magical constants that change depending on where they are used. For example, the value of __LINE__ depends on the line that it's used on in your script. All these "magical" constants are resolved at compile time, unlike regular constants, which are resolved at runtime. These special constants are case-insensitive and are as follows:

PHP's magic constants
Denumire Descriere
__LINE__ The current line number of the file.
__FILE__ The full path and filename of the file with symlinks resolved. If used inside an include, the name of the included file is returned.
__DIR__ The directory of the file. If used inside an include, the directory of the included file is returned. This is equivalent to dirname(__FILE__). This directory name does not have a trailing slash unless it is the root directory.
__FUNCTION__ The function name, or {closure} for anonymous functions.
__CLASS__ The class name. The class name includes the namespace it was declared in (e.g. Foo\Bar). When used in a trait method, __CLASS__ is the name of the class the trait is used in.
__TRAIT__ The trait name. The trait name includes the namespace it was declared in (e.g. Foo\Bar).
__METHOD__ The class method name.
__NAMESPACE__ The name of the current namespace.
ClassName::class The fully qualified class name.

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User Contributed Notes 9 notes

up
285
vijaykoul_007 at rediffmail dot com
18 years ago
the difference between
__FUNCTION__ and __METHOD__ as in PHP 5.0.4 is that

__FUNCTION__ returns only the name of the function

while as __METHOD__ returns the name of the class alongwith the name of the function

class trick
{
      function doit()
      {
                echo __FUNCTION__;
      }
      function doitagain()
      {
                echo __METHOD__;
      }
}
$obj=new trick();
$obj->doit();
output will be ----  doit
$obj->doitagain();
output will be ----- trick::doitagain
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38
Tomek Perlak [tomekperlak at tlen pl]
17 years ago
The __CLASS__ magic constant nicely complements the get_class() function.

Sometimes you need to know both:
- name of the inherited class
- name of the class actually executed

Here's an example that shows the possible solution:

<?php

class base_class
{
    function
say_a()
    {
        echo
"'a' - said the " . __CLASS__ . "<br/>";
    }

    function
say_b()
    {
        echo
"'b' - said the " . get_class($this) . "<br/>";
    }

}

class
derived_class extends base_class
{
    function
say_a()
    {
       
parent::say_a();
        echo
"'a' - said the " . __CLASS__ . "<br/>";
    }

    function
say_b()
    {
       
parent::say_b();
        echo
"'b' - said the " . get_class($this) . "<br/>";
    }
}

$obj_b = new derived_class();

$obj_b->say_a();
echo
"<br/>";
$obj_b->say_b();

?>

The output should look roughly like this:

'a' - said the base_class
'a' - said the derived_class

'b' - said the derived_class
'b' - said the derived_class
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12
david at thegallagher dot net
12 years ago
You cannot check if a magic constant is defined. This means there is no point in checking if __DIR__ is defined then defining it. `defined('__DIR__')` always returns false. Defining __DIR__ will silently fail in PHP 5.3+. This could cause compatibility issues if your script includes other scripts.

Here is proof:

<?php
echo (defined('__DIR__') ? '__DIR__ is defined' : '__DIR__ is NOT defined' . PHP_EOL);
echo (
defined('__FILE__') ? '__FILE__ is defined' : '__FILE__ is NOT defined' . PHP_EOL);
echo (
defined('PHP_VERSION') ? 'PHP_VERSION is defined' : 'PHP_VERSION is NOT defined') . PHP_EOL;
echo
'PHP Version: ' . PHP_VERSION . PHP_EOL;
?>

Output:
__DIR__ is NOT defined
__FILE__ is NOT defined
PHP_VERSION is defined
PHP Version: 5.3.6
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10
php at kenman dot net
9 years ago
Just learned an interesting tidbit regarding __FILE__ and the newer __DIR__ with respect to code run from a network share: the constants will return the *share* path when executed from the context of the share.

Examples:

// normal context
// called as "php -f c:\test.php"
__DIR__ === 'c:\';
__FILE__ === 'c:\test.php';

// network share context
// called as "php -f \\computerName\c$\test.php"
__DIR__ === '\\computerName\c$';
__FILE__ === '\\computerName\c$\test.php';

NOTE: realpath('.') always seems to return an actual filesystem path regardless of the execution context.
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10
Sbastien Fauvel
7 years ago
Note a small inconsistency when using __CLASS__ and __METHOD__ in traits (stand php 7.0.4): While __CLASS__ is working as advertized and returns dynamically the name of the class the trait is being used in, __METHOD__ will actually prepend the trait name instead of the class name!
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11
chris dot kistner at gmail dot com
12 years ago
There is no way to implement a backwards compatible __DIR__ in versions prior to 5.3.0.

The only thing that you can do is to perform a recursive search and replace to dirname(__FILE__):
find . -type f -print0 | xargs -0 sed -i 's/__DIR__/dirname(__FILE__)/'
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4
meindertjan at gmail dot spamspamspam dot com
10 years ago
A lot of notes here concern defining the __DIR__ magic constant for PHP versions not supporting the feature. Of course you can define this magic constant for PHP versions not yet having this constant, but it will defeat its purpose as soon as you are using the constant in an included file, which may be in a different directory then the file defining the __DIR__ constant. As such, the constant has lost its *magic*, and would be rather useless unless you assure yourself to have all of your includes in the same directory.

Concluding: eye catchup at gmail dot com's note regarding whether you can or cannot define magic constants is valid, but stating that defining __DIR__ is not useless, is not!
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0
public at taliesinnuin dot net
3 years ago
If you're using PHP with fpm (common in this day and age), be aware that __DIR__ and __FILE__ will return values based on the fpm root which MAY differ from its actual location on the file system.

This can cause temporary head-scratching if deploying an app where php files within the web root pull in PHP files from outside of itself (a very common case). You may be wondering why __DIR__ returns "/" when the file itself lives in /var/www/html or whathaveyou.

You might handle such a situation by having NGINX explicitly add the necessary part of the path in its fastcgi request and then you can set the root on the FPM process / server / container to be something other than the webroot (so long as no other way it could become publicly accessible).

Hope that saves someone five minutes who's moving code to FPM that uses __DIR__.
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-39
Anonymous
12 years ago
Further clarification on the __TRAIT__ magic constant.

<?php
trait PeanutButter {
    function
traitName() {echo __TRAIT__;}
}

trait
PeanutButterAndJelly {
    use
PeanutButter;
}

class
Test {
    use
PeanutButterAndJelly;
}

(new
Test)->traitName(); //PeanutButter
?>
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