Required files to compile in a C++ project:

firmasat.hpp
diFirmaSat2.h
firmasat.cpp
  #include "diFirmaSat2.h"
  #include "firmasat.hpp"
{main}.cpp
  #include "firmasat.hpp"
  int main() { ... }

You must link to diFirmaSAT2.lib. In MSVC++ IDE, use Project > Properties > Linker > Input > Additional Dependencies and add the full path to diFirmaSAT2.lib. E.g.

Additional Dependencies = $(OutDir)diFirmaSAT2.lib;%(AdditionalDependencies)

Using the command-line with MSVC:

CL test.cpp firmasat.cpp /link ..\Debug\diFirmaSAT2.lib

Using GCC (make sure the DLL has been compiled for target X64):

g++ -std=c++11 test.cpp firmasat.cpp "C:\fullpath\to\x64\Debug\diFirmaSAT2.lib"

Here is a simple C++ (STL) program for testing.

#include <iostream>
#include "firmasat.hpp"
int main()
{
    std::cout << "Gen::Version=" << firmasat::Gen::Version() << std::endl;
}