Is php backward compatible?

PHP adopts a downward compatible upgrade method for major versions, which means that 5.5 is compatible with 5.1-5.4. Having said that, the actual compatibility is not optimistic.

Recommended: php server

The developers of the PHP language have put a lot of effort into backward compatibility, so under the new version of PHP, the code of the old version should Can (ideally) run without any changes. But in reality, some changes must be made to the old code.

The two most important changes that may affect the old version of the code are:

1. The old $HTTP_*_VARS array will no longer be valid starting from PHP 5.4.0. PHP » Version 4.1.0 introduces the following superglobal array variables: $_GET, $_POST, $_COOKIE, $_SERVER, $_FILES, $_ENV, $_REQUEST and $_SESSION.

2. External variables are no longer registered as global variables by default. In other words, starting from PHP » 4.2.0 version, the default value of the setting option register_globals in php.ini becomes off. It is recommended to use the superglobal array variables mentioned above to access these values.

But maybe old scripts, books, and tutorials may be based on this setting being on. If this option is set to on, the variable $id can be used directly in the URL http://www.example.com/foo.php?id=42. But regardless of whether it is set to on or off, $_GET['id'] is always valid.

The above is the detailed content of Is php backward compatible?. For more information, please follow other related articles on the PHP Chinese website!