#ifdef _WIN32 not getting detected

Question

I can not get the #ifdef rule to work at least on windows (64 bit). Compiler version is g++ 5.4.0 I have tried:

#ifdef _WIN32
#ifdef _WIN64
#ifdef OS_WINDOWS

I have compiled the following test with: g++ main.cpp

Even with a simple code as this:

#include <iostream>

int main()
{
  std::cout << "you are on...";

  #ifdef _WIN32
  std::cout << "Windows" << std::endl;
  #elif __linux__
  std::cout << "Linux" << std::endl;
  #endif

  return 0;
}

Output is:

"you are on..."

...and nothing else gets couted out.

Possible duplicate of [How do I check OS with a preprocessor directive?](http://stackoverflow.com/questions/142508/how-do-i-check-os-with-a-preprocessor-directive) — Algirdas Preidžius, Jan 11 '17 at 13:12
Are you *compiling* on Windows? Or just *running* on Windows? — Cory Kramer, Jan 11 '17 at 13:12
G++... is that a MinGW or a Cygwin compiler? AFAICR, Cygwin doesn't set `_WIN32` because it isn't, it's a POSIX environment. — DevSolar, Jan 11 '17 at 13:13
And.. Why do you expect anything to be printed out if you are on 64-bit Windows, and are only checking for 32-bit windows, and Linux? — Algirdas Preidžius, Jan 11 '17 at 13:13
@AlgirdasPreidžius: `_WIN32` should be defined for 32 **and** 64-bit Windows, as per documentation. — DevSolar, Jan 11 '17 at 13:14
@AlgirdasPreidžius - `_WIN32` is standard for both 32-bit and 64-bit windows. It's a Windows thing. — selbie, Jan 11 '17 at 13:14
@DevSolar Oh, I see. I wrote my comment before checking the full list of defined variables, present in the answer, of the linked question.. Thanks for correcting me :) — Algirdas Preidžius, Jan 11 '17 at 13:16
I have dumbed the list of defines as the Ville-Valtteri Tiittanen pointed out, but I can not sure what I should be looking for from that list. — Mikko-Pentti Einari Eronen, Jan 11 '17 at 13:18
@Mikko-PenttiEinariEronen Do you have anything in there that looks like an operating system name? If not, it might be that G++ does not define that by default. — VLL, Jan 11 '17 at 13:21
On Cygwin and/or the bash shell that was introduced for Win10, there really should be no expectation of any `WIN32` being defined. Because these environments are trying to emulate Unix. Not sure about MinGW, where it's possible to use the Windows SDK. — selbie, Jan 11 '17 at 13:21
@selbie: MinGW GCC defines `_WIN32`, as it should. (Even when run on Linux as a cross-compiler.) — DevSolar, Jan 11 '17 at 13:28

score 11 · Accepted Answer · edited Jun 20 '20 at 09:12

#ifdef _WIN32
#ifdef _WIN64

These are pre-defined macros defined by the MSVC compiler. You appear to be using g++ instead. That probably means either MinGW, or Cygwin.

Here and here are collections of macros pre-defined by several compilers.

MinGW __MINGW32__

Cygwin __CYGWIN__

If you prefer to not to build hefty ifdef - else trees, and scour the internet for macros defined by obscure compilers, and their different versions, I recommend to instead include a few headers from boost. They have already done the hard part of the work. Although, note that BOOST_OS_WINDOWS is separate from BOOST_OS_CYGWIN.

I thank you all for the help and efford. This clears things up quite a bit for me. — Mikko-Pentti Einari Eronen, Jan 11 '17 at 13:26

score 3 · Answer 2 · answered Jan 11 '17 at 13:21

Use __CYGWIN32__ to detect Windows when compiling g++ in cygwin. (This is defined in both 32 and 64 bit).

_WIN32 &c. may not be defined in that case. It isn't for me.

(As also mentioned in a comment; using echo | g++ -dM -E to output the list of what is defined can be helpful.)

score -2 · Answer 3 · answered Oct 18 '20 at 20:34

-2

yes, it is true that this:

#ifdef _WIN32

sometimes doesn't work on Windows (!) In this case, use the following form instead:

#if defined(_WIN32)

I was surprised but I have seen that problem and it helped me!

answered Oct 18 '20 at 20:34

Łukasz Gotszald

7
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#ifdef _WIN32 not getting detected

3 Answers3