The meaning of a variable that starts with an underscore in PHP

Named rules

• Add one for private

• Add two is usually the system default, the system is predefined, that is, the so-called: "Magic Method" and "Magic constant"
  

The constant that PHP starts and ends with double underlines is "magic constant":

The current line number in the __line__ file.

The full path and file name of the __file__ file.

The directory where the __dir__ 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

Note: The above is from the "PHP Chinese Manual, language Reference, constant-and magic constant".

From the later version of PHP5, the PHP class will be able to use the Magic method.

PHP rules to start with two underscore (__) methods are preserved as a magic method, it is recommended that the function name is best not to start without __, unless it is to reload the existing magic method.

The Magic Methods in PHP are: __construct, __destruct, __call, __callstatic,__get, __set, __isset, __unset, __sleep, __wakeup, __toString, __set_state, __clone, __autoload

__autoload

The __autoload function, which is called automatically when trying to use a class that has not yet been defined. By calling this function, the scripting engine has the last chance to load the required classes before PHP fails.

If you are defining a global auto-load class, you must register the processing class with the PHP standard library using the Spl_autoload_register () method:

<?php    class loader     {        static function autoload_ Class ($class _name)         {         //look for the right $class_name class, and introduce, no then throw an exception         }     }        /**  *   Setting Object Auto-loading   *   spl_autoload_register - register given function as __autoload ()   Implementation  */    spl_autoload_register (Array (' Loader ',  ' Autoload_class ');         $a  = new test ();//test does not use require on the instantiation, realizes the automatic loading, Many frameworks use this method to automatically load class         ?> 

Note: Exceptions thrown in the __autoload function cannot be caught by a catch statement block and cause a fatal error, so the function itself should be captured.

(Original post: http://blog.csdn.net/zlking02/article/details/6752256)

The meaning of a variable that starts with an underscore in PHP