The CVI compiler supports ANSI C, not C++. You cannot use CVI to compile C++ code.
There are a couple of ways CVI works together with C++. To use existing C++ code within CVI, you can use a C++ compiler to create a DLL and call DLL functions from CVI. From with C++, you can load and call CVI library functions. C++ compilers can compile C, but ANSI C compilers (including CVI) can't compile C++.