怎么在编译时检查操作系统类型

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C/C++ tip: How to detect the operating system type using compiler predefined macros

January 3, 2012

Topics: C/C++

Table of Contents

1. How to list predefined macros
2. How to detect the operating system type
   1. AIX
   2. BSD
   3. HP-UX
   4. Linux
   5. OSX, iOS, and Darwin
   6. Solaris
   7. Windows with Cygwin (POSIX)
   8. Windows, Cygwin (non-POSIX), and MinGW
3. How to detect POSIX and UNIX
   1. POSIX
   2. UNIX
4. Other ways to detect the operating system type
5. Further reading
   1. Related articles at NadeauSoftware.com
   2. Web articles

How to list predefined macros

See How to list compiler predefined macros for instructions on getting a list of macros for the compilers referenced here.

How to detect the operating system type

Throughout the following sections note:

• Red text indicates deprecated macros that don't start with an underscore. C++ compilers, and C compilers in standards compliance mode, do not define them.
• Green text indicates recommended macros that are well-supported and useful for detecting a specific OS.

AIX

Developer:IBMDistributions:AIXProcessors:POWER

#if defined(_AIX)/* IBM AIX. ------------------------------------------------- */#endif

AIXMacroGNU GCC/G++IBM XL C/C++_AIXyesyes__unix yes__unix__yesyes

Notes:

• See IBM's notes on Using the GNU C/C++ compiler on AIX.

BSD

Developer:Open sourceDistributions:DragonFly BSD, FreeBSD, OpenBSD, NetBSDProcessors:x86, x86-64, Itanium, POWER, SPARC, etc.

#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))#include <sys/param.h>#if defined(BSD)/* BSD (DragonFly BSD, FreeBSD, OpenBSD, NetBSD). ----------- */#endif#endif

BSDMacroClang/LLVMGNU GCC/G++DragonFly BSDFreeBSDNetBSDOpenBSDFreeBSDNetBSDOpenBSDunixyesyes yesyes  __unixyesyes yesyes  __unix__yesyesyesyesyesyesyes__DragonFly__yes      __FreeBSD__ yes  yes  __NetBSD__  yes  yes __OpenBSD__   yes  yes

Notes:

• Compilers for the old BSD base for these distributions defined the __bsdi__ macro, but none of these distributions define it now. This leaves no generic "BSD" macro defined by the compiler itself, but all UNIX-style OSes provide a <sys/param.h> file. On BSD distributions, and only on BSD distributions, this file defines a BSD macro that's set to the OS version. Checking for this generic macro is more robust than looking for known BSD distributions with__DragonFly__, __FreeBSD__, __NetBSD__, and __OpenBSD__ macros.
• Apple's OSX for the Mac and iOS for iPhones and iPads are based in part on a fork of FreeBSD distributed as Darwin. As such, OSX and iOS also define the BSD macro within <sys/param.h>. However, compilers for OSX, iOS, and Darwin do not define __unix__. To detect all BSD OSes, including OSX, iOS, and Darwin, use an #if/#endif that checks for __unix__ along with __APPLE__ and __MACH__ (see the later section on OSX and iOS).

HP-UX

Developer:Hewlett-PackardDistributions:HP-UXProcessors:Itanium

#if defined(__hpux)/* Hewlett-Packard HP-UX. ----------------------------------- */#endif

HP-UXMacroGNU GCC/G++HP C/aC++hpuxyes __hpuxyesyesunixyes __unixyesyes__unix__yes 

Linux

Developer:Open sourceDistributions:Centos, Debian, Fedora, OpenSUSE, RedHat, UbuntuProcessors:x86, x86-64, POWER, etc.

#if defined(__linux__)/* Linux. --------------------------------------------------- */#endif

LinuxMacroClang/LLVMGNU
GCC/G++Intel
ICC/ICPCOracle
Solaris StudioPortland 
PGCC/PGCPPIBM
XL C/C++linuxyesyesyesyesyes __linuxyesyesyesyesyesyes__linux__yesyesyesyesyesyes__gnu_linuxyesyesyesyes  unixyesyesyesyesyes __unixyesyesyesyesyesyes__unix__yesyesyesyesyesyes

Notes:

• Linux is available for a wide variety of processors, but it is primarily used on x86 and x86-64 processors. The above table's compilers are all for these processors. Some of them may not be available for other processors.
• There are no predefined compiler macros indicating the specific Linux distribution. At run-time you can read /proc/version to get the distribution name and version, or invoke uname -a from a Makefile then set your own macro. However, writing Linux distribution-specific code is rarely necessary due to high compatibility between distributions.
• Linux is POSIX compliant and defines the standard _POSIX* macros in <unistd.h>. While Linux is compliant with the latest POSIX.1-2008 specification, Linux distributions erroneously set _POSIX_VERSION to 200809L, instead of leaving it set to 200112L, as required by the POSIX specification. In practice, this is not a big issue since the existence, not value, of the _POSIX_VERSION macro is sufficient to detect POSIX compliance. After that, the individual_POSIX_* feature macros provide better information about which specific POSIX features are implemented (see later in this article for POSIX discussion).

OSX, iOS, and Darwin

Developer:Apple and open sourceDistributions:OSX, iOS, DarwinProcessors:x86, x86-64, ARM

#if defined(__APPLE__) && defined(__MACH__)/* Apple OSX and iOS (Darwin). ------------------------------ */#include <TargetConditionals.h>#if TARGET_IPHONE_SIMULATOR == 1/* iOS in Xcode simulator */#elif TARGET_OS_IPHONE == 1/* iOS on iPhone, iPad, etc. */#elif TARGET_OS_MAC == 1/* OSX */#endif#endif

OSX and DarwinMacroClang/LLVMGNU
GCC/G++Intel
ICC/ICPCPortland 
PGCC/PGCPP__APPLE__yesyesyesyes__MACH__yesyesyesyesiOSMacroClang/LLVMGNU GCC/G++__APPLE__yesyes__MACH__yesyes

Notes:

• For Apple's OSes, all compilers define __APPLE__ and __MACH__ macros. The __MACH__ macro indicates the MACH kernel at the heart of OSX/iOS and partially derived from the obsolete NeXTSTEP. For rigor, both of these macros must be defined to detect OSX/iOS. If only __MACH__ is defined, the OS is NeXTSTEP or one of the other OSes derived from the MACH kernel.
• All OSX compilers are available from the command-line. Apple's Xcode IDE can be configured to invoke any of them from the GUI.
• Mac OSX and iOS include BSD UNIX components originally from FreeBSD. The open source parts of Mac OSX and iOS are distributed as Darwin,without Apple's proprietary user interface and tools. Despite being UNIX-like, Mac OSX and iOS compilers do not define the conventional __unix__, __unix, or unix macros. They do define the BSD macro in <sys/param.h> (see later discussion about BSD).
• Some on-line lists of compiler macros (like this one) list __MACOSX__. Some forum comments (like these) claim __OSX__ exists. These are incorrect. There are no such macros predefined by OSX compilers, but they may be defined by specific project Makefiles and platform-detector scripts like GNU autoconf.
• Some lists (like this one) still include macintosh or Macintosh macros. These were only available on the obsolete Mac OS 9 discontinued back in 2002.
• Some forum advice and books (like this one) claim that the __APPLE__ macro is only defined by Apple's own compilers. This is incorrect. While it's true that compilers distributed by Apple define this macro, so do OSX distributions of Intel's ICC, the old IBM XL for PowerPC, and the latest direct downloads of Clang and GCC from open source web sites.
• OSX and iOS compilers do not define macros to distinguish between OSX and iOS. However, Apple's <TargetConditionals.h> in each platform's SDK provides TARGET_* macros that indicate the OS. All of the macros exist for all platforms, but their values change between 0 and 1 flags as follows: Mac OSXiOSiOS SimulatorTARGET_OS_EMBEDDED010TARGET_OS_IPHONE011TARGET_OS_MAC111TARGET_IPHONE_SIMULATOR001TargetConditionals.h
• Note that the above macros are not mutually exclusive: TARGET_OS_MAC is set to 1 for all platforms, and TARGET_OS_IPHONE is 1 for iOS and the simulator. To detect OSX vs. iOS vs. the iOS simulator you have to check the macro values in a specific order (see below).
• There are no macros to distinguish at compile time between an iPhone, iPad, or other Apple devices using the same OSes.

Solaris

Developer:Oracle and open sourceDistributions:Oracle Solaris, Open IndianaProcessors:x86, x86-64, SPARC

#if defined(__sun) && defined(__SVR4)/* Solaris. ------------------------------------------------- */#endif

SolarisMacroClang/LLVMGNU GCC/G++Oracle Solaris Studiosunyesyesyes__sunyesyesyes__sun__yesyes __SunOS  yes__svr4__yesyes __SVR4yesyesyesunixyesyesyes__unixyesyesyes__unix__yesyes 

Notes:

• To conform with long-standing convention, Solaris compilers define __sun and sun, despite Oracle's acquisition of Sun Microsystems in 2010. Clang and GCC also define __sun__, but Solaris Studio does not.
• Oracle compilers do not define an "oracle" macro or a "solaris" macro.
• Checking for __sun is not sufficient to identify Solaris. Compilers for the obsolete BSD-based SunOS also defined __sun (and Solaris Studio still defines__SunOS, even on System V-based Solaris). To identify Solaris specifically, the __sun and __SVR4 macros must be defined. Also note that you need to check for upper-case __SVR4 instead of the lower-case __svr4 that's only defined by GCC and not by Solaris Studio.

Windows with Cygwin (POSIX)

Developer:Open sourceDistributions:CygwinProcessors:x86

#if defined(__CYGWIN__) && !defined(_WIN32)/* Cygwin POSIX under Microsoft Windows. -------------------- */  #endif

Cygwin building for POSIXMacroClang/LLVMGNU GCC/G++__CYGWIN__yesyes__CYGWIN32__yesyesunixyesyes__unixyesyes__unix__yesyes

Notes:

• Cygwin provides a POSIX development environment for Windows, including shells, command-line tools, and compilers. Using Cygwin's libraries, POSIX applications can be built and run under Windows without any Windows-specific code.

• Cygwin POSIX libraries are 32-bit-only, so 64-bit POSIX applications cannot be built. Some code found on-line references __CYGWIN64__. However, there is no 64-bit Cygwin, so this macro is never defined. It exists only in forum discussions about a possible future 64-bit Cygwin.
• Clang/LLVM and GCC both can build POSIX or Windows applications. The table above shows macros when building POSIX applications. See the Windows section later in this article for macros when building Windows applications. Comparing the macro set for both types of applications note that __CYGWIN__and the standard __unix__ macros are always defined by GCC, even when building a Windows application. For this reason, detecting POSIX builds under Cygwin must use an #if/#endif that checks that __CYGWIN__ is defined, but _WIN32 is not.
• Checking for Cygwin POSIX builds probably isn't necessarily at all. The whole point of Cygwin is to run standard POSIX applications under Windows, so checking for Cygwin explicitly shouldn't be needed.
• Intel's compilers are not supported under Cygwin, but users have hacked running them from a Cygwin bash command line. However, the compilers still build Windows applications, not POSIX applications.
• Portland Group's compilers for Windows come with a Cygwin install that enables the compilers to be run from a bash command-line, but they still build Windows applications, not POSIX applications.

Windows, Cygwin (non-POSIX), and MinGW

Developer:MicrosoftDistributions:Windows XP, Vista, 7, 8Processors:x86, x86-64

#if defined(_WIN64)/* Microsoft Windows (64-bit). ------------------------------ */#elif defined(_WIN32)/* Microsoft Windows (32-bit). ------------------------------ */  #endif

WindowsMacroClang/LLVM
(Windows target)Clang/LLVM
(MinGW target)
GNU
GCC/G++
(Windows target)GNU
GCC/G++
(MinGW target)Intel
ICC/ICPCPortland 
PGCC/PGCPPMicrosoft 
Visual Studio32-bit64-bit32-bit64-bit32-bit32-bit64-bit32-bit64-bit32-bit64-bit32-bit64-bit__CYGWIN__    yes        __CYGWIN32__    yes        __MINGW32__  yesyes yesyes      __MINGW64__   yes  yes      unix    yes        __unix    yes        __unix__    yes        WIN32  yes yesyesyes      _WIN32yesyesyesyesyesyesyesyesyesyesyesyesyes__WIN32  yes yesyesyes  yesyes  __WIN32__  yes yesyesyes  yesyes  WIN64   yes  yes      _WIN64 yes yes  yes yes yes yes__WIN64   yes  yes   yes  __WIN64__   yes  yes   yes  WINNT  yes yesyesyes      __WINNT  yes  yesyes      __WINNT__  yes  yesyes      

Notes:

• Clang/LLVM and GCC under Windows run within the Cygwin POSIX environment or the MinGW minimal GNU environment. Both provide a bash shell and assorted command-line utilities. Cygwin also provides POSIX libraries while MinGW does not.
• Based on command-line options, the Clang/LLVM and GCC compilers can build Windows applications or POSIX applications that run under Windows using POSIX compatibility libraries. Predefined macros for POSIX applications are described in the previous section of this article. The table above is strictly for compiling Windows applications.
• Clang/LLVM can build Windows applications using the Windows target (e.g. "-ccc-host-triple i386-pc-win32") or the MinGW target (e.g. "-ccc-host-triple i386-pc-mingw32"). The "-m32" option builds 32-bit applications and "-m64" builds 64-bit.
• GCC under Cygwin can build Windows applications using the "-mwin32" command-line option. While GCC is capable of building 64-bit applications, Cygwin is 32-bit only and the version of GCC included with it only builds 32-bit applications.
• Oddly enough, GCC under Cygwin predefines UNIX macros even when building Windows applications.
• Some on-line code references __CYGWIN64__. Since there is no 64-bit Cygwin, this macro is never defined. It exists only in forum discussions about a possible future 64-bit Cygwin.
• GCC under MinGW can build Windows applications using the "-mwin32" command-line option. The "-m32" and "-m64" options build 32-bit and 64-bit applications.
• While Clang/LLVM, GCC, and Portland Group compilers define a lot of WIN32 and WIN64 macros with various numbers of underscores, the only macros that matter are those that are compatible with Microsoft's Visual Studio: _WIN32 and _WIN64.
• Some on-line advice recommends checking for _MSC_VER. The macro is defined with the compiler version number for Clang/LLVM, ICC, and Visual Studio, but it isn't defined by GCC or Portland Group compilers.
• Some lists of predefined macros (like this one) include additional macros for discontinued products, such as __TOS_WIN__ for IBM's XL compiler on Windows (XL is still available for AIX and Linux), and __WINDOWS__ for the discontinued but open sourced Watcom compiler.

How to detect POSIX and UNIX

POSIX and UNIX are not operating systems. Rather they are formal or de facto standards followed to some degree by all UNIX-style OSes.

POSIX

Developer:StandardDistributions:All current UNIX-style OSes, including BSD, Linux, OSX, and SolarisProcessors:x86, x86-64, ARM, POWER, SPARC, etc.

#if !defined(_WIN32) && (defined(__unix__) || defined(__unix) || (defined(__APPLE__) && defined(__MACH__)))/* UNIX-style OS. ------------------------------------------- */#include <unistd.h>#if defined(_POSIX_VERSION)/* POSIX compliant */#endif#endif

All UNIX-style OSes (see also UNIX below) have <unistd.h> that defines macros indicating the level of POSIX compliance. The _POSIX_VERSION macro value indicates the version of the standard with which the OS is compliant. Known values are:

• 198808L for POSIX.1-1988
• 199009L for POSIX.1-1990
• 199506L for ISO POSIX.1-1996
• 200112L for ISO POSIX.1-2001
• 200809L for ISO POSIX.1-2008

Another way to detect ISO POSIX.1-2008 compliance is with a run-time check using sysconf.

if ( sysconf( _SC_VERSION ) >= 200809L ){  /* POSIX.1-2008 */}else{  /* Pre-POSIX.1-2008 */}

While the #if/#endif and sysconf call above will both work to detect broad POSIX compliance, it's more useful to check for individual POSIX features flagged by macros in <unistd.h>. The POSIX specification has a long list of these macros, but a few of the more useful ones include:

• _POSIX_IPV6 indicates IPv6 address support.
• _POSIX_MAPPED_FILES indicates memory mapping support.
• _POSIX_SEMAPHORES indicates semaphore support for multi-threading.
• _POSIX_THREADS indicates pthreads support. A number of _POSIX_THREAD* macros then indicate whether thread resource usage can be reported or thread scheduling priority controlled.

UNIX

Developer:De facto standardDistributions:All current UNIX-style OSes, including BSD, Linux, OSX, and SolarisProcessors:x86, x86-64, ARM, POWER, SPARC, etc.

#if !defined(_WIN32) && (defined(__unix__) || defined(__unix) || (defined(__APPLE__) && defined(__MACH__)))/* UNIX-style OS. ------------------------------------------- */#endif

UNIX (Clang/LLVM compilers)MacroCygwin (POSIX)DragonFly BSDFreeBSDiOSLinuxNetBSDOpenBSDOSXSolarisunixyesyesyes yes yes yes__unixyesyesyes yes yes yes__unix__yesyesyes yesyesyes yesUNIX (GCC compilers)MacroAIXCygwin (POSIX)FreeBSDiOSHP-UXLinuxNetBSDOpenBSDOSXSolarisunix yesyes yesyes   yes__unix yesyes yesyes   yes__unix__yesyesyes yesyesyesyes yesUNIX (Other compilers) AIXHP-UXLinuxOSXSolarisMacroIBM
XL C/C++HP
C/aC++Intel
ICC/ICPCOracle
Solaris StudioPortland 
PGCC/PGCPPIBM
XL C/C++Intel
ICC/ICPCPortland 
PGCC/PGCPPOracle
Solaris Studiounix  yesyesyes   yes__unixyesyesyesyesyesyes  yes__unix__yes yesyesyesyes   

Notes:

• There is no single UNIX macro defined by all compilers on all UNIX-style OSes. An #if/#endif that checks multiple macros is required.
• Compilers for Apple's OSX and iOS don't define any UNIX macros. An #if/#endif that checks __APPLE__ and __MACH__ is required (see the earlier section OSX and iOS).
• GCC under Cygwin defines UNIX macros even when building Windows applications. An #if/#endif that excludes _WIN32 is required to detect UNIX builds on Cygwin (see the earlier section on Windows).

Other ways to detect the operating system type

On UNIX-style OSes a common way to detect OS features is to use GNU's autoconf. This tool builds configuration shell scripts that automatically check for OS and compiler features, build Makefiles, and set compiler flags. For code that only targets UNIX-style OSes, this works well. But autoconf doesn't work for code that must compile on non-UNIX-style OSes (e.g. Windows) or within an IDE. And it's way overkill for many projects where a simple #if/#endif set will do.

From the command line there are several ways to detect the OS. On UNIX-style OSes, the uname command reports the OS name. On Windows, the ver andwinver commands report the OS name. On Linux, the /proc/version virtual file reports the Linux kernel version. But using any of these to automatically configure code requires scripts and Makefiles. And those have the same problems as autoconf.

The most elegant solution is to eschew all detection scripts and simply use the above predefined macros already available on every OS and designed specifically for use in #if/#endif sets for OS-specific code. Don't reinvent the wheel.

Further reading

Related articles at NadeauSoftware.com

• C/C++ tip: How to list compiler predefined macros explains how to get a compiler's macros by using command-line options and other methods.
• C/C++ tip: How to detect the compiler name and version using compiler predefined macros provides #if/#endif sets for detecting common compilers.
• C/C++ tip: How to detect the processor type using compiler predefined macros provides #if/#endif sets for detecting desktop and server processors using compiler macros.

Web articles

• Operating Systems at Sourceforge.net provides a list of OSes and their compiler predefined macros. However the list is cluttered with obsolete OSes (OS/2? Palm OS?), doesn't note macros shared across many OSes (like __unix__), and doesn't include discussion.
• Pre-defined C/C++ Compiler Macros at beefchunk.com has a list of OSes and predefined macros. Like the Sourceforge list, the information is a bit cluttered with obsolete OSes (DG/UX? Unicos?) and lacks discussion.
• Operating System Resources at Apache.org has a good list of OSes, links to vendor documentation, and some tables of compiler predefined macros.