WoW:Getting the current interface number
There are a few reasons why you might need the most current Interface version number. Usually you are a mod author and need to specify it in your .TOC file. It would look like:
##Interface: 1600
But how do you get this number? If you boot up WoW, there is a version number displayed but this number is wrong.
Current
The current Interface version number for WoW 1.6.1 on 2005-07-31 is:
1600
Steal It
Chances are someone else has beaten you to it, and already updated their addon to the latest version, and you might already have the updated version, especially for addon packages with a .exe updater. Simply open one of their addon's .toc files to see the valid interface number.
This number might be wrong, or you may not have any up to date addons, or you may feel horrible for ripping someone else's hard work.
Do it yourself
This is a bit more tricky. What you want is to find the interface number in Blizzard's FrameXML.toc file after a patch -- but this file is buried in a MPQ archive! While blizzard provides an Extraction Tool it will extract all the current files! If you want to save on diskspace, read on:
You need to grab WinMPQ but wait! Because WoW's patch.MPQ file is so big, the old WinMPQ program will crash with a 'overflow' error! Instead you need to grab this patched WinMPQ program.
Install it, then open:
World of Warcraft\Data\patch.mpq
From there, find the line that says:
Interface\FrameXML\FrameXML.toc
click it, then click extract. Put it somewhere you can access, and open it in your favorite text editor. Look the ##Interface line, and voila! The newest interface version number is in your hands, to be used in all your addons. Please remember that just changing the ##Interface line does not mean the mod will work, the code, structure and functions for addons can change after a patch, so check the patch notes and your favorite UI forums to see if you need to update any of your code before re-releasing your addon!