@taketwo Based on this seems true. But looking at our pcl_macros.h, I see both definitions being used. Should we suggest to change to

#if defined WIN32 || defined _WIN32

?

Usage of these macros in pcl_macros.h is inconsistent, see e.g. lines 172 and 180. Unfortunately, I'm not a Windows user, so can not comment on which one is the preferred.

From what I'm seeing here and here I'm more convinced that _WIN32 is the standard way of doing it and WIN32 is something that normally also works because

1. The user included some windows headers which defined it
2. MSVC also appears to add it although it's not exactly a standard

@UnaNancyOwen any relevant comments you might give us on this discussion?

Nevertheless, I have the feeling this should be good to merge.

It is correct that @SergioRAgostinho said.
Microsoft-specific predefined macros | MSDN Library

#include <iostream>

int main()
{
    // Defined as 1 when include header that WIN32 is defined (such as windows.h), or set define WIN32 in preprocessor definition.
    // "WIN32" is user-defined flags.
    std::cout << "WIN32 : ";
#ifdef WIN32
    std::cout << "Defined" << std::endl;
#else
    std::cout << "Undefined" << std::endl;
#endif

    // Defined as 1 when compilation target is 32-bit ARM, 64-bit ARM, x86, or x64.
    // "_WIN32" is compiler-defined flags.
    // That is, _WIN32 is always defined by compiler when using MSVC.
    std::cout << "_WIN32 : ";
#ifdef _WIN32
    std::cout << "Defined" << std::endl;
#else
    std::cout << "Undefined" << std::endl;
#endif

    return 0;
}

MSVC output is following.

WIN32 : Undefined
_WIN32 : Defined

Super nice explanation. Thanks @UnaNancyOwen