Redefinition of VirtualAllocEx

I believe MSVC++ 6 supports namespaces, and I think you have the perfect situation to apply them.  Encase all of your declarations in their own namespace, as in

namespace afeijao {
typedef LPVOID (WINAPI *VIRTUALALLOCEX)(HANDLE, LPVOID, DWORD, DWORD, DWORD);
VIRTUALALLOCEX       VirtualAllocEx;
// ... other declarations
}

At this point, it can all be referenced as "afeijao::VirtualAllocEx()" after you set the function pointer to the correct address.

It might also be possible to confine all of microsoft's header files to their own namespace, as in

namespace MS {
#include <windows.h>
}

which should cause microsoft's VirtualAllocEx to be reached by MS::VirtualAllocEx();.

If you have your objects in one namespace, and microsoft's in another, you get to pick and choose with the using directive as follows:

namespace MS {
#include <windows.h>
}

namespace afeijao {
typedef LPVOID (WINAPI *VIRTUALALLOCEX)(HANDLE, LPVOID, DWORD, DWORD, DWORD);
VIRTUALALLOCEX       VirtualAllocEx;
// ... other declarations
}

using MS::CreateThread;
using afeijao::VirtualAllocEx;

would result in CreateThread() using microsoft's header, and VirtualAllocEx() using your function pointer.

I hope I've been clear enough on this topic.

cplusplus.com has an easy to understand namespace tutorial at
http://www.cplusplus.com/doc/tutorial/tut5-2.html

MSDN's namespace documentation is more complete, albeit harder to navigate at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccelng/htm/tions_37.asp

The namespace solution seems a good compromise.
The only problem is that it only works for C++.
Is there a way of using namespaces in C/SDK (which I'm using) without converting the whole project to C++ ?

Well, if you are compiling the C code AS C code, your only solution would be to mangle the names of your function pointers.  C is for the most part, though, a subset of C++, and if you are compiling it as C++ code, which you should be able to get away with, you can add in namespaces, or any other C++ features as you see fit.

I would like to keep my code strait C.

Do you know if there's a way to #undef a function ?

(more information on winver at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winprog/winprog/using_the_windows_headers.asp )