C++: Tidy MainWindow

[fallenshadow]

My question is more coding related in general but I am using C++ for my project. I guess I've been wondering lately at what point do you consider doing a tidy of a main file and start putting functions in another file? My main file is around 1300 lines long and its already a bit convoluted.

Also with C++ what is the best way to tidy functions away but still call them in the main file?

Thanks in advance to anyone who will advise.

[fallenshadow]

To expand upon this. Most functions are called from either Toolbars or Menus. Should I just bundle functions into menu files. Like FileMenu.cpp, EditMenu.cpp for example. Just looking for opinions on a good structure, I know I can throw things into a new source/header file(s).