Win APIs on windows 8

Dear Experts,

I'm doing my migration of my own coding application (C++) from Win XP to Win 8.
I'm concerning the Win APIs compatibility.
The main question is "Will my used API work well on Win 8 as same as it used to do on Win XP".

I found that, in Win XP (C:\Windos\System32\) there's some dll like user32.dll, kernel32.dll,....
But in windows 8 (C:\Windows\System32), there're:
   +  not only user32.dll and kernel32.dll
   +  but also api-ms-win-....dll and \downlevel\api-ms-win-....dll (such as api-ms-win-core-heap-l1-1-0.dll)
So, please explain me,
   +  What's api-ms-win-....dll stand for?
   +  Does this make any trouble to compatibility of Win APIs.

Regarding your soon responses.
With best regards.
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>>The main question is "Will my used API work well on Win 8 as same as it used to do on Win

The answer is both "Yes" and "No". As with your other Q, the API calls will behave the same, yet the result might be different regarding file system and registry virtualization and UAC as mentioned in ("Making Your Application UAC Aware" - I know I posted that in your last question as well, just to be complete).

The "api-ms-win[...].dll" things that you see are new to W8, yet nothing else but helpers - see ("Windows API Sets"):

API Sets are strongly named API contracts that provide architectural separation between an API contract and the associated host (DLL) implementation. API Sets rely on operating system support in the library loader to effectively introduce a namespace redirection component to the library binding process. Subject to various inputs, including the API Set name and the binding (import) context, the library loader performs a runtime redirection of the reference to a target host binary that houses the appropriate implementation of the API Set.

So, these are basically helpers to nake it easier for your app to end up at the set of functions that they want, yet no change in functionality will occur, especially for binaries compiled for earlier versions.

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Windows 8

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