Using old code with new versions of PHP

Now that PHP has grown to be a popular scripting language, there are more resources out there that have listings of code you can reuse in your own scripts. For the most part the developers of the PHP language have tried to be backwards compatible, so a script written for an older version should run (ideally) without changes in a newer version of PHP, in practice some changes will usually be needed.

Two of the most important recent changes that affect old code are:

For more details on these changes, see the section on predefined variables and links therein.