"Now I want to use this piece of code in a written Project in C++, but when I added that very same code to a new C++ project ... "
That probably won't work. If this code is in a .cpp in a C++ project, it won't work.
cusp is a template library that is built on top of thrust which is built on top of CUDA, so cusp codes must be compiled by nvcc
, i.e. it must be in a CUDA project in VS, not an ordinary C++ project.
So go back to using a CUDA project in VS for your cusp codes.