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

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On MinGW  the  WIN32 define check isn t working  Here s a solution    if defined  WIN32     defined   CYGWIN           Windows  x86 or x64              elif defined   linux           Linux             elif defined   APPLE     amp  amp  defined   MACH           Mac OS             elif defined unix     defined   unix       defined   unix         Unix like OS             else      error Unknown environment   endif   For more information please look  https   sourceforge net p predef wiki OperatingSystems

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There is no standard macro that is set according to C standard  Some C compilers will set one on some platforms  e g  Apple s patched GCC sets a macro to indicate that it is compiling on an Apple system and for the Darwin platform   Your platform and or your C compiler might set something as well  but there is no general way   Like hayalci said  it s best to have these macros set in your build process somehow  It is easy to define a macro with most compilers without modifying the code  You can simply pass -D MACRO to GCC  i e   gcc -D Windows gcc -D UNIX   And in your code    if defined Windows     do some cool Windows stuff  elif defined UNIX     do some cool Unix stuff  else      error Unsupported operating system  endif

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Based on nadeausoftware and Lambda Fairy s answer   include  lt stdio h gt          Determination a platform of an operation system    Fully supported supported only GNU GCC G    partially on Clang LLVM       if defined  WIN32       define PLATFORM NAME  quot windows quot     Windows  elif defined  WIN64       define PLATFORM NAME  quot windows quot     Windows  elif defined   CYGWIN     amp  amp   defined  WIN32       define PLATFORM NAME  quot windows quot     Windows  Cygwin POSIX under Microsoft Window   elif defined   ANDROID         define PLATFORM NAME  quot android quot     Android  implies Linux  so it must come first   elif defined   linux         define PLATFORM NAME  quot linux quot     Debian  Ubuntu  Gentoo  Fedora  openSUSE  RedHat  Centos and other  elif defined   unix        defined   APPLE     amp  amp  defined   MACH         include  lt sys param h gt       if defined BSD           define PLATFORM NAME  quot bsd quot     FreeBSD  NetBSD  OpenBSD  DragonFly BSD      endif  elif defined   hpux       define PLATFORM NAME  quot hp-ux quot     HP-UX  elif defined  AIX       define PLATFORM NAME  quot aix quot     IBM AIX  elif defined   APPLE     amp  amp  defined   MACH       Apple OSX and iOS  Darwin       include  lt TargetConditionals h gt       if TARGET IPHONE SIMULATOR    1          define PLATFORM NAME  quot ios quot     Apple iOS      elif TARGET OS IPHONE    1          define PLATFORM NAME  quot ios quot     Apple iOS      elif TARGET OS MAC    1          define PLATFORM NAME  quot osx quot     Apple OSX      endif  elif defined   sun   amp  amp  defined   SVR4       define PLATFORM NAME  quot solaris quot     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     quot  quot    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

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Microsoft C C   compiler  MSVC  Predefined Macros can be found here I think you are looking for     WIN32 - Defined as 1 when the compilation target is 32-bit ARM  64-bit ARM  x86  or x64  Otherwise  undefined  WIN64 - Defined as 1 when the compilation target is 64-bit ARM or x64  Otherwise  undefined    gcc compiler PreDefined MAcros can be found here I think you are looking for      GNUC     GNUC MINOR     GNUC PATCHLEVEL     Do a google for your appropriate compilers pre-defined

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I wrote an small library to get the operating system you are on  it can be installed using clib  The C package manager   so it is really simple to use it as a dependency for your projects   Install    clib install abranhe os c   Usage   include  lt stdio h gt   include  os h   int main         printf   s n   operating system            macOS     return 0      It returns a string  char   with the name of the operating system you are using  for further information about this project check it out the documentation on Github

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Use  define OSsymbol and  ifdef OSsymbol where OSsymbol is a  define able symbol identifying your target OS   Typically you would include a central header file defining the selected OS symbol and use OS-specific include and library directories to compile and build   You did not specify your development environment  but I m pretty sure your compiler provides global defines for common platforms and OSes   See also http   en wikibooks org wiki C Programming Preprocessor

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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 nbsp  nbsp  nbsp Both 32 bit and 64 bit  WIN64 nbsp  nbsp  nbsp 64 bit only  Unix  Linux   BSD  Mac OS X   See this related question on some of the pitfalls of using this check   unix   unix   unix    Mac OS X    APPLE     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

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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

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Some compilers will generate  defines that can help you with this  Read the compiler documentation to determine what they are  MSVC defines one that s   WIN32    GCC has some you can see with touch foo h  gcc -dM foo h

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You can use pre-processor directives as warning or error to check at compile time you don t need to run this program at all just simply compile it     if defined  WIN32     defined  WIN64     defined   WINDOWS         error Windows OS  elif defined   linux         error Linux OS  elif defined   APPLE     amp  amp  defined   MACH         error Mach OS  elif defined unix     defined   unix       defined   unix       error Unix OS  else      error Unknown OS  endif   include  lt stdio h gt  int main void        return 0

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show GCC defines on Windows   gcc -dM -E -  lt NUL    on Linux   gcc -dM -E -  lt  dev null   Predefined macros in MinGW   WIN32  WIN32   WIN32   WIN32     MINGW32   WINNT   WINNT   WINNT    X86  i386   i386   on UNIXes   unix   unix     unix

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I did not find Haiku definition here  To be complete  Haiku-os definition is simple   HAIKU

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Sorry for the external reference  but I think it is suited to your question  C C   tip  How to detect the operating system type using compiler predefined macros

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You can use Boost Predef which contains various predefined macros for the target platform including the OS  BOOST OS     Yes boost is often thought as a C   library  but this one is a preprocessor header that works with C as well   This library defines a set of compiler  architecture  operating system  library  and other version numbers from the information it can gather of C  C    Objective C  and Objective C   predefined macros or those defined in generally available headers  The idea for this library grew out of a proposal to extend the Boost Config library to provide more  and consistent  information than the feature definitions it supports  What follows is an edited version of that brief proposal   For example  include  lt boost predef h gt    if defined BOOST OS WINDOWS   elif defined BOOST OS ANDROID   elif defined BOOST OS LINUX   elif defined BOOST OS BSD   elif defined BOOST OS AIX   elif defined BOOST OS HAIKU       endif  The full list can be found in BOOST OS operating system macros See also How to get platform ids from boost

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ifdef  WIN32    do something for windows like include  lt windows h gt   elif defined   unix      do something for unix like include  lt unistd h gt   elif defined   APPLE      do something for mac  endif

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Just to sum it all up  here are a bunch of helpful links    GCC Common Predefined Macros SourceForge predefined Operating Systems MSDN Predefined Macros The Much-Linked NaudeaSoftware Page Wikipedia    SourceForge s  Overview of pre-defined compiler macros for standards  compilers  operating systems  and hardware architectures   FreeBSD s  Differentiating Operating Systems  All kinds of predefined macros libportable

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