Well unfortunaley C++ does not have a standard GUI library. Microsoft never thought to optimize that method like they did with Visual Basic and C#. You will most likely have to build your form and use the Form.ShowMethod(). You can see more on that in the following link:
Unless of course the NX comes pre-packaged with a GUI library for C++. I'm not sure. I think you will have to resort to using the above method.
I don't use C++. but I thought you could access all the old C stuff from there...
Lenovo ThinkPad W540, Win7, 16GB. Developing in: Java | C | KF
Production: NX22.214.171.124 MP11 64bit Testing: NX126.96.36.199
If you search for uc1607 in the Solution Center, and then filter on the document type of nx_api, there are 72 example programs available that use that function.
You can add Open C into your Opdn C++ code, just be sure that you #include <uf_ui.h> - or whatever header is appropriate for the call you are using.