PHP Magic Constants

PHP Manual-"Language Reference-" constants-"Magic Constants"

PHP provides a large number of predefined constants to any script it runs. However, many constants are defined by different extensions, and are only present when the extensions are loaded, either dynamically after loading, or they are included at compile time.

There are eight magic constants whose values change as they change position in the code . For example __LINE__ , a value depends on the row it is in the script to determine. these Special constants are case-insensitive, as follows:

(1)__file__

the full path and filename of the file . If used in the included file, returns the file name that is included. Since PHP 4.0.2, __FILE__ always contains an absolute path (if the symbolic connection is the resolved absolute path), and the previous version sometimes contains a relative path.

(2)__dir__

the directory where the file resides . If used in the included file, returns the directory where the included files are located. It is equivalent to dirname (__file__). Unless it is a root directory, the name in the directory does not include the trailing slash. (New in PHP 5.3.0)

PHP Magic Constants