How to open a folder in %appdata% with C++?

Question

As you all know, the appdata folder is this

 C:\Users\*Username*\AppData\Roaming

on windows 7

Since my application will be deployed on all kinds of Windows OSes i need to be able to get the folder 100% percent of the time. The question is how do you do it in C++? Since i don't know the the exact Windows OS it could be XP,Vista or 7 and most importantly i don't know what the Username is.