Magic variables
Magic variables refer to those that have different values according to different environments
For example,
__FILE__
is a typical magic variable. When it When it appears in the a.php file, its value is the specific path of a.php. When it appears in the b.php file, it is the specific path of b.php
. Some other magic variables include __FUNCTION__, __CLASS__
In short, the values of these variables are often not fixed, but change around, very magical, like magic, so they are called magic variables
Magic variables include:
__LINE__ The current line number in the file.
__FILE__ The full path and file name of the file. If used within an included file, returns the name of the included file. Since PHP 4.0.2, __FILE__ always contains an absolute path (or the resolved absolute path in the case of a symbolic link), whereas versions before that sometimes contained a relative path.
__DIR__ The directory where the file is located. If used within an included file, returns the directory where the included file is located. It is equivalent to dirname(__FILE__). Directory names do not include the trailing slash unless they are the root directory. (New in PHP 5.3.0) =
__FUNCTION__ Function name (New in PHP 4.3.0). Since PHP 5 this constant returns the name of the function as it was defined (case sensitive). In PHP 4 this value is always lowercase.
__CLASS__ The name of the class (newly added in PHP 4.3.0). Since PHP 5 this constant returns the name of the class when it was defined (case sensitive). In PHP 4 this value is always lowercase.
__METHOD__ The method name of the class (newly added in PHP 5.0.0). Returns the name of the method as it was defined (case-sensitive).
__NAMESPACE__ The name of the current namespace (case sensitive). This constant is defined at compile time. __TRAIT__ Trait is a new feature in PHP5.4 and is a solution to PHP multiple inheritance. For example, it would be very troublesome to inherit two Abstract Classes at the same time. Trait is designed to solve this problem.
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