‘unistd.h’ is native to POSIX-compliant systems, i’ve heard of a couple equivalents out there, but i think it depends on the functions you’re trying to grab from it, but most of them usually lie in ‘windows.h’

if unistd.h is necessary with no equivalents for your code, the only case it would work is in a POSIX environment, which means anything based in UNIX (a macOS may also be able to do the trick, but keep in mind not every OS is fully compatible with POSIX)