Quote Originally Posted by krs0 View Post
OK. Now I can access struct's members when I catch WM_INITDIALOG in my custom onInitDialog().

I still do not understand how to access/pass this struct from/to onButtonClicked().
Do you or don't use any C++ framework? If you do, Arjay is right, and you never need it be a separate structure. But if you don't, you need to invent some mechanism that allows the structure address be found by dialog window handle. Global map, or SetProp/GetProp typically do the trick.