Commenter asdf wonders where WIN32_LEAN_AND_MEAN came from. The WIN32_LEAN_AND_MEAN symbol was introduced in the Windows 95 time frame as a way to exclude a bunch of Windows header files when you include windows.h. You can take a look at your windows.h file to see which ones they are. The symbol was added as part of the transition from 16-bit Windows to 32-bit Windows. The 16-bit windows.h header file didn’t include all of those header files, and defining WIN32_LEAN_AND_MEAN brought you back to the 16-bit Windows philosophy of a minimal set of header files for writing a bare-bones Windows program. This appeased the programmers who liked to micro-manage their header files, and it was a big help because, at the time the symbol was introduced, precompiled header files were not in common use. As I recall, on a 50MHz 80486 with 8MB of memory, switching to WIN32_LEAN_AND_MEAN shaved three seconds off the compile time of each C file. When your project consists of 20 C files, that’s a whole minute saved right there.

Moore’s Law and precompiled headers have conspired to render the WIN32_LEAN_AND_MEAN symbol relative useless. It doesn’t really save you much any more. But at one point, it did.