Constants
PHP Manual

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 thats resolved at runtime. These special constants are case-insensitive and are as follows:

A few "magical" PHP constants
Name Description
__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.
__CLASS__ The class name. The class name includes the namespace it was declared in (e.g. Foo\Bar). Note that as of PHP 5.4 __CLASS__ works also in traits. 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. See also ::class.

See also get_class, get_object_vars, file_exists and function_exists.

Changelog

Version Description
5.5.0 Added ::class magic constant
5.4.0 Added __TRAIT__ constant
5.3.0 Added __DIR__ and __NAMESPACE__ constants
5.0.0 Added __METHOD__ constant
5.0.0 Before this version values of some magic constants were always lowercased. All of them are case-sensitive now (contain names as they were declared).
4.3.0 Added __FUNCTION__ and __CLASS__ constants
4.0.2 __FILE__ always contains an absolute path with symlinks resolved whereas in older versions it contained relative path under some circumstances