It's MFC code.
Remember also that MFC is quite old. It reinvents a lot of stuff that C++ now supports natively, but back in the day, C++ did not support. That is why, sometimes, it can be a lot of code.
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.