If you are using g++ on Linux*, you will get an error. If you are using Microsoft* C++ on Windows*, you will not get an error, but it does not generate any code.
Intel® C++ is serious about compatibility. On Linux, it will give an error. On Windows, there is no error and no code generated. Of course, Intel C++ has options that override these behaviors if you would like the error on Windows, too.
Quickly improve performance without rewriting a single line of code
What if you are close to release but your program is still slow and sluggish? Intel C++ is known for generating fast code. If you know the hotspot in your program, try recompiling just that file with Intel C++ and see if your program speeds up. This mixing works because Intel C++ is not just source compatible, it is also binary compatible.
If you would like to learn more about finding hotspots and recompiling with Intel C++ on Windows to enhance performance, check out the Intel® Evaluation Guide, "Get an Easy Performance Boost Even with Unthreaded Apps."
Be the expert who can quickly improve performance without rewriting a single line of code!