Thank you, much appreciated!
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BTW.....another modification uses something like this to call files from vbulletin:
<a href=<?php echo get_option('vbb_VBURL') ?>/showthread.php?t=<?php echo $vbridge[id] ?>>(<?php echo intval($vbridge[count]) ?>) comments</a>
It's from the Wordpress/vBulletin integration mod. (https://vborg.vbsupport.ru/showthread.php?t=134521)
Again....I have no idea what I am talking about and this probably isn't a help. I was just throwing it out there, seeing if it would be relevant at all.
Anything I just wrote just got dumped because my iMac just randomly shut off. But I will tell you why that won't work...
This is how they are fetching your vBulletin URL:
<?php echo get_option('vbb_VBURL') ?>
The function get_option goes into WordPress' option table to find the value you ask for, in this case vbb_VBURL, and will return the value. And that is linking to your vBulletin. I am not sure if you do that.
Now back to rewriting that post for you. :(
-- EDIT --
Here's what I whipped up:
The Basics
Basically, what you are doing to "link" your main site to your vBulletin installation is by using vBulletin code to access things like cookies, database, and other data. So, if you know vBulletin's code base (and I assume you do since you have a Coder title) you have a good head start.
Linking The Platforms
All I believe you have to do, since most of this code is untested, is require ./forum/global.php since this is what sets and includes most of the files within your main vBulletin installation.
After that, if you need specific classes or functions is doing require('./forum/includes/functions_X.php');
File Paths
Most likely, global.php will spit out "Could Not Find File" errors (actually it's PHP that spits out the errors). You will be told a file and line number. Go to the line number in the specified file and change the relative path (something like ./includes/class_user.php) and change them to an absolute path (something like /home/www/youraccount/forum/includes/class_user.php). That way it will know the exact location.
Sadly, upgrading will overwrite the file paths so you will have to re do them. That's why a constant or "relative" constant would be useful in coding your site to revolve around vBulletin.