OK, so I decided it was about time I learn how to break up my sources into smaller files. I read the article on GameDev and the FAQ here. I have the basic jest of it, but I'm still having trouble with the global variables.
I have a global vector declared in a header file that is included in every source file. When I declare it like this, using extern:
extern vector <unit> myUnits;
I get errors about "undefined references to myUnits"
When I leave off the extern I get errors about multiple definition of myUnits. Not sure what I need to do to fix it.