Question

Is there any way to build a VC++ project so that the dll/exe created by it will work as a 32 bit application on a 32 bit Windows OS and as a 64 bit application on a 64 bit Windows OS (not in WOW64).

I know that is possible for C# applications using the /ANYCPU option.

Answer 1

The CLR has special loader support for the /ANYCPU option.

If you really want to do this for native, the best way to do it is to:

1. Build your binary for both 32- and 64-bit
2. As part of building the 32-bit binary, include the 64-bit binary as a resource
3. On 32-bit machines, just run the 32-bit binary
4. On 64-bit machines, when the 32-bit binary runs, unpack the 64-bit binary resource, write it to disk, and run it from there

This is how the Sysinternals tools work (download Process Explorer onto a 64-bit machine and run it: you’ll see that it writes procexp64.exe to disk and then runs it from there). It’s a hack, but it works.