Learning PHP, MySQL, and JavaScript

PHP Version Compatibility

PHP is in an ongoing process of development, and there are multiple versions. If you need to check whether a particular function is available to your code, you can use the function_exists function, which checks all predefined and user-created functions.

Example 5-9 checks for the function array_combine, which is specific to PHP version 5.

Example 5-9. Checking for a function’s existence

<?php
if (function_exists("array_combine"))
{
    echo "Function exists";
}
else
{
    echo "Function does not exist - better write our own";
}
?>

Using code such as this, you can take advantage of features in newer versions of PHP and yet still have your code run on earlier versions, as long as you replicate any features that are missing. Your functions may be slower than the built-in ones, but at least your code will be much more portable.

You can also use the phpversion function to determine which version of PHP your code is running on. The returned result will be similar to the following, depending on version:

5.2.8