[kh99]

Originally Posted by richy96

...I guess really I need to know where the code for $userdata->set() is before i could answer that myself, which is what I am asking here

$userdata is an object of class vB_DataManager_User. If you look near the beginning of register.php you see that $userdata comes from a call to datamanager_init() which is in includes/functions.php. Essentially it's the result of a "new vB_DataManager_User()'. The code for class vB_DataManager_User is in includes/class_dm_user.php, and since it extends class vB_DataManager, some relevant code will be in includes/class_dm.php.

I believe set() sets a property in the object, and a later call to save() will actually write stuff to the database (and I believe presave() is called when all the set()'s are doen but before the actual database write). There might be info somewhere else on the site about using data managers but I don't know offhand where.

In case you're not familiar with object oriented stuff it's probably worth reading over this section of the php manual: http://us2.php.net/manual/en/language.oop5.php

Also what exactly is GPC() it crops up a lot but I have never really understood it (or had the need to yet)

GPC is an array of the "cleaned" values input to the script from get (params on the url), post (form data), and cookies. Again looking at the top of register.php you see calls to clean_gpc, this takes the specified input values and makes sure they are of a specified type (for example if it's supposed to be an integer it makes sure the value is all digits, etc), then inserts it the in the GPC[] array. The code for that is in includes/class_core.php, in class vB_Input_Cleaner.

Now this fetch_hook thing is something that has me totally puzzled.

fetch_hook() is part of the plugin system. If you add a plugin (in the admin control panel) using hook location 'register_addmember_process', then the code you enter will be returned by the call to fetch_hook('register_addmember_process') and the eval will "run" it, so that it's as if the code was in the file at that point. It's nice to be able to do modifications entirely through hooks because then you don't modify the php files and updating to a new version of vB becomes a whole lot easier.