Migrating from PHP 3 to PHP 4
PHP Manual

PHP 3 extension

Extensions written for PHP 3 will not work with PHP 4, neither as binaries nor at the source level. It is not difficult to port extensions to PHP 4 if you have access to the original source. A detailed description of the actual porting process is not part of this text.


Migrating from PHP 3 to PHP 4
PHP Manual