How do I check OS with a preprocessor directive?

Question

I need my code to do different things based on the operating system on which it gets compiled. I'm looking for something like this:

#ifdef OSisWindows
// do Windows-specific stuff
#else
// do Unix-specific stuff
#endif

Is there a way to do this? Is there a better way to do the same thing?

Solution 1

The Predefined Macros for OS site has a very complete list of checks. Here are a few of them, with links to where they're found:

Windows

_WIN32   Both 32 bit and 64 bit
_WIN64   64 bit only
__CYGWIN__

Unix (Linux, *BSD, but not Mac OS X)

See this related question on some of the pitfalls of using this check.

unix
__unix
__unix__

Mac OS X

__APPLE__ Also used for classic
__MACH__

Both are defined; checking for either should work.

Linux

__linux__
linux Obsolete (not POSIX compliant)
__linux Obsolete (not POSIX compliant)

FreeBSD

__FreeBSD__

Android

__ANDROID__

Solution 2

show GCC defines on Windows:

gcc -dM -E - <NUL:

on Linux:

gcc -dM -E - </dev/null

Predefined macros in MinGW:

WIN32 _WIN32 __WIN32 __WIN32__ __MINGW32__ WINNT __WINNT __WINNT__ _X86_ i386 __i386

on UNIXes:

unix __unix__ __unix

Solution 3

Based on nadeausoftware and Lambda Fairy's answer.

#include <stdio.h>

/**
 * Determination a platform of an operation system
 * Fully supported supported only GNU GCC/G++, partially on Clang/LLVM
 */

#if defined(_WIN32)
    #define PLATFORM_NAME "windows" // Windows
#elif defined(_WIN64)
    #define PLATFORM_NAME "windows" // Windows
#elif defined(__CYGWIN__) && !defined(_WIN32)
    #define PLATFORM_NAME "windows" // Windows (Cygwin POSIX under Microsoft Window)
#elif defined(__ANDROID__)
    #define PLATFORM_NAME "android" // Android (implies Linux, so it must come first)
#elif defined(__linux__)
    #define PLATFORM_NAME "linux" // Debian, Ubuntu, Gentoo, Fedora, openSUSE, RedHat, Centos and other
#elif defined(__unix__) || !defined(__APPLE__) && defined(__MACH__)
    #include <sys/param.h>
    #if defined(BSD)
        #define PLATFORM_NAME "bsd" // FreeBSD, NetBSD, OpenBSD, DragonFly BSD
    #endif
#elif defined(__hpux)
    #define PLATFORM_NAME "hp-ux" // HP-UX
#elif defined(_AIX)
    #define PLATFORM_NAME "aix" // IBM AIX
#elif defined(__APPLE__) && defined(__MACH__) // Apple OSX and iOS (Darwin)
    #include <TargetConditionals.h>
    #if TARGET_IPHONE_SIMULATOR == 1
        #define PLATFORM_NAME "ios" // Apple iOS
    #elif TARGET_OS_IPHONE == 1
        #define PLATFORM_NAME "ios" // Apple iOS
    #elif TARGET_OS_MAC == 1
        #define PLATFORM_NAME "osx" // Apple OSX
    #endif
#elif defined(__sun) && defined(__SVR4)
    #define PLATFORM_NAME "solaris" // Oracle Solaris, Open Indiana
#else
    #define PLATFORM_NAME NULL
#endif

// Return a name of platform, if determined, otherwise - an empty string
const char *get_platform_name() {
    return (PLATFORM_NAME == NULL) ? "" : PLATFORM_NAME;
}

int main(int argc, char *argv[]) {
    puts(get_platform_name());
    return 0;
}

Tested with GCC and clang on:

• Debian 8
• Windows (MinGW)
• Windows (Cygwin)

Solution 4

In most cases it is better to check whether a given functionality is present or not. For example: if the function pipe() exists or not.

Solution 5

#ifdef _WIN32
// do something for windows like include <windows.h>
#elif defined __unix__
// do something for unix like include <unistd.h>
#elif defined __APPLE__
// do something for mac
#endif

View more solutions

Comments

[John_West]

@Cory Klein: No-no. this question has been asked years-before

[ilgaar]

This is about C not C++

[phuclv]

How to detect reliably Mac OS X, iOS, Linux, Windows in C preprocessor?, Detect Windows or Linux in C, C++

[Akib Azmain]

@CoryKlein No, that question is a duplicate of this question.

[Cory Klein]

@AkibAzmain You’ve pulled me back into history! Wow what an old question. It was already 5 years old when I first commented 7 years ago! Interestingly, comparative age isn’t definitive criteria for selecting which is the duplicate, but in this case it looks like the other was marked as the duplicate ages ago so it’s a moot question. Have a good day!

[hayalci]

is there an easy way to check out if a function is defined ?

[quinmars]

If you are using autoconfig you can check for functions with AC_CHECK_FUNCS(). AC_CHECK_FUNCS(pipe sqrt) will define HAVE_PIPE and HAVE_SQRT if the functions are available. I don't know how it is with other building tools, but I guess they also support this in a way.

[Gary Makin]

This site given does not include iOS, so it fails to be able to distinguish between iOS and OS X.

[Sebi2020]

gcc: error: unrecognized command line option '--show-defines' gcc: fatal error: no input files compilation terminated.

[PADYMKO]

the dear @MD XF, please indicate versions of your Windows, MinGW and Cygwin

[MD XF]

Windows 7 Enterprise 6.1.7601. Cygwin 2.7.0-1. I can't find the MinGW version but I downloaded it yesterday.

[MD XF]

You should probably be made aware though - this program is standard C, so it should work on all compliant systems.

[MD XF]

That meta post was removed. Funny that a meta post asking about posts removed for reasons of moderation was removed for reasons of moderation.

[PADYMKO]

dear @MD XF, thank you for this information. I added you as contributor on top this answer.

[Konstantin Burlachenko]

:) Yeah. Absolutely crazy

[Victor Sergienko]

Mac OS does not define __unix__. Why would you include it in the list?

[katta]

cpp -dM /dev/null will give you a list of all the gcc predefined macro on your version of installed gcc

[David Given]

Cygwin defines the unix symbols and doesn't define the win32 ones, so be careful. OTOH it does define __CYGWIN__.

[Alcaro]

@MDXF As of C++17, there is __has_include. I don't think it's standardized in C yet, but all major compilers (GCC, Clang, ICC, MSVC) implement it as a vendor-specific extension, even in C mode.

[phuclv]

Windows and Unices are not the only OSes

[Admin]

is __linux__ same as __ANDROID__ ??

[Ayxan Haqverdili]

Why is __linux not POSIX compliant?

[Ayxan Haqverdili]

The Windows link is broken

[Mikhail Zakharov]

_AIX for IBM AIX respectively.

[mklement0]

That's handy, but note that unix, __unix__, __unix don't work on macOS, where only __APPLE__ and __MACH__ are defined.

[Polluks]

@AyxanHaqverdili not enough underscores

[mercury]

best answer as it covers cygwin.