Why does MAKEINTRESOURCE() work?

Question

The macro is defined as:

#define MAKEINTRESOURCEA(i) ((LPSTR)((ULONG_PTR)((WORD)(i))))
#define MAKEINTRESOURCEW(i) ((LPWSTR)((ULONG_PTR)((WORD)(i))))
         


        

Answer 1

This works because Windows doesn't allow mapping pages for the first 64 KB of the address space. To catch null pointer references. But I think also to catch pointer bugs in programs that were converted from the 16-bit version of Windows.

A side-effect is that this allows to reliably distinguish resource IDs packed into a pointer value since they'll always point to non-mappable memory.