serialize extension objects?

I'm writing an extension for PHP 4 (running version 4.3.10) in C/C++. The extension provides a set of classes to the PHP programmer (it is, hence, object oriented). My problem is that some of the objects (or, rather, references to objects) provided by my extension needs to be stored in a session and, thus, serialized. I have, however, no idea on how to provide a custom serialize function for my objects as the built-in one (for obvious reasons) doesn't work. I have had no luck finding any useful tips and/or documentation for PHP 4 regarding this matter. I sincerely hope that someone could point me in the right direction. Or have I completely misunderstood the entire concept; when storing a reference to an object (implemented in C/C++), do the object really have to be serialized? Thanks for all tips! :-) Best regards David Olsson