Does anyone know how to make a stopwatch function in C++ (emacs) that runs on a Unix OS?

I tried using sys/time.h but it says the file is not found and I usually don't program on Unix at all but it is required for a class and I have no idea what to do.





I also need to make the timer start when the user presses a key.

Does anyone know how to make a stopwatch function in C++ (emacs) that runs on a Unix OS?
At the link is a simple timer example.