Everything you allocate through any C function (not API) is virtual. It is only limited by the amount of virtual memory (we are talking about high-level OSes like Linux, Windows, Mac here).
Virtual memory is limited to a number of OS factors.
Originally Posted by Adak
io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
Originally Posted by Salem
You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.
Outside of your DOS world, your header file is meaningless.