Should I define both _WIN32 and _WIN64 in 64bit build?

Question

When we add a 64bit configuration from a 32bit project that has already existed, Visual Studio copies the 32bit configurations by default. VS even copies _WIN32

Answer 1

The documentation for the predefined macros says:

_WIN32: Defined for applications for Win32 and Win64. Always defined.

_WIN64: Defined for applications for Win64.

So not only should _WIN32 always be defined, it does not cause any problem in 64-bit applications. Therefore, I'd suggest you don't remove it.