C/C++ tip: How to detect the operating system type using compiler predefined macros
转自：http://nadeausoftware.com/articles/2012/01/c_c_tip_how_use_compiler_predefined_macros_detect_operating_system#OSXiOSandDarwin
OS identification macros are predefined by all C/C++ compilers to enable #if/#endif sets to wrap OS-specific code. This is often necessary in cross-platform code that must use low-level library functions for fast disk I/O, inter-process communications, or threads. While differences between Windows and other OSes are acute, even differences among UNIX-style OSes can require #if/#endif constructs.This article surveys common compilers and shows how to use predefined macros to detect common OSes at compile time.
Table of Contents
- How to list predefined macros
- How to detect the operating system type
- AIX
- BSD
- HP-UX
- Linux
- OSX, iOS, and Darwin
- Solaris
- Windows with Cygwin (POSIX)
- Windows, Cygwin (non-POSIX), and MinGW
- How to detect POSIX and UNIX
- POSIX
- UNIX
- Other ways to detect the operating system type
- Further reading
- Related articles at NadeauSoftware.com
- 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: | IBM |
| Distributions: | AIX |
| Processors: | POWER |
#if defined(_AIX) /* IBM AIX. ------------------------------------------------- */ #endif
| Macro | GNU GCC/G++ | IBM XL C/C++ |
|---|---|---|
_AIX |
yes | yes |
__unix |
yes | |
__unix__ |
yes | yes |
Notes:
- See IBM's notes on Using the GNU C/C++ compiler on AIX.
BSD
| Developer: | Open source |
| Distributions: | DragonFly BSD, FreeBSD, OpenBSD, NetBSD |
| Processors: | 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
| Macro | Clang/LLVM | GNU GCC/G++ | |||||
|---|---|---|---|---|---|---|---|
| DragonFly BSD | FreeBSD | NetBSD | OpenBSD | FreeBSD | NetBSD | OpenBSD | |
unix |
yes | yes | yes | yes | |||
__unix |
yes | yes | yes | yes | |||
__unix__ |
yes | yes | yes | yes | yes | yes | yes |
__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 aBSDmacro 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
BSDmacro 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/#endifthat checks for__unix__along with__APPLE__and__MACH__(see the later section on OSX and iOS).
HP-UX
| Developer: | Hewlett-Packard |
| Distributions: | HP-UX |
| Processors: | Itanium |
#if defined(__hpux) /* Hewlett-Packard HP-UX. ----------------------------------- */ #endif
| Macro | GNU GCC/G++ | HP C/aC++ |
|---|---|---|
hpux |
yes | |
__hpux |
yes | yes |
unix |
yes | |
__unix |
yes | yes |
__unix__ |
yes |
Linux
| Developer: | Open source |
| Distributions: | Centos, Debian, Fedora, OpenSUSE, RedHat, Ubuntu |
| Processors: | x86, x86-64, POWER, etc. |
#if defined(__linux__) /* Linux. --------------------------------------------------- */ #endif
| Macro | Clang/LLVM | GNU GCC/G++ |
Intel ICC/ICPC |
Oracle Solaris Studio |
Portland PGCC/PGCPP |
IBM XL C/C++ |
|---|---|---|---|---|---|---|
linux |
yes | yes | yes | yes | yes | |
__linux |
yes | yes | yes | yes | yes | yes |
__linux__ |
yes | yes | yes | yes | yes | yes |
__gnu_linux |
yes | yes | yes | yes | ||
unix |
yes | yes | yes | yes | yes | |
__unix |
yes | yes | yes | yes | yes | yes |
__unix__ |
yes | yes | yes | yes | yes | yes |
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/versionto get the distribution name and version, or invokeuname -afrom aMakefilethen 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_VERSIONto200809L, instead of leaving it set to200112L, as required by the POSIX specification. In practice, this is not a big issue since the existence, not value, of the_POSIX_VERSIONmacro 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 source |
| Distributions: | OSX, iOS, Darwin |
| Processors: | 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
| Macro | Clang/LLVM | GNU GCC/G++ |
Intel ICC/ICPC |
Portland PGCC/PGCPP |
|---|---|---|---|---|
__APPLE__ |
yes | yes | yes | yes |
__MACH__ |
yes | yes | yes | yes |
| Macro | Clang/LLVM | GNU GCC/G++ |
|---|---|---|
__APPLE__ |
yes | yes |
__MACH__ |
yes | yes |
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 obsoleteNeXTSTEP. 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, orunixmacros. They do define theBSDmacro in<sys/param.h>(see laterdiscussion 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 GNUautoconf. - Some lists (like this one) still include
macintoshorMacintoshmacros. 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 providesTARGET_*macros that indicate the OS. All of the macros exist for all platforms, but their values change between0and1flags as follows:Mac OSX iOS iOS Simulator TARGET_OS_EMBEDDED010TARGET_OS_IPHONE011TARGET_OS_MAC111TARGET_IPHONE_SIMULATOR001TargetConditionals.h - Note that the above macros are not mutually exclusive:
TARGET_OS_MACis set to1for all platforms, andTARGET_OS_IPHONEis1for 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 source |
| Distributions: | Oracle Solaris, Open Indiana |
| Processors: | x86, x86-64, SPARC |
#if defined(__sun) && defined(__SVR4) /* Solaris. ------------------------------------------------- */ #endif
| Macro | Clang/LLVM | GNU GCC/G++ | Oracle Solaris Studio |
|---|---|---|---|
sun |
yes | yes | yes |
__sun |
yes | yes | yes |
__sun__ |
yes | yes | |
__SunOS |
yes | ||
__svr4__ |
yes | yes | |
__SVR4 |
yes | yes | yes |
unix |
yes | yes | yes |
__unix |
yes | yes | yes |
__unix__ |
yes | yes |
Notes:
- To conform with long-standing convention, Solaris compilers define
__sunandsun, 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
__sunis 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__sunand__SVR4macros must be defined. Also note that you need to check for upper-case__SVR4instead of the lower-case__svr4that's only defined by GCC and not by Solaris Studio.
Windows with Cygwin (POSIX)
| Developer: | Open source |
| Distributions: | Cygwin |
| Processors: | x86 |
#if defined(__CYGWIN__) && !defined(_WIN32)
/* Cygwin POSIX under Microsoft Windows. -------------------- */
#endif
| Macro | Clang/LLVM | GNU GCC/G++ |
|---|---|---|
__CYGWIN__ |
yes | yes |
__CYGWIN32__ |
yes | yes |
unix |
yes | yes |
__unix |
yes | yes |
__unix__ |
yes | yes |
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/#endifthat checks that__CYGWIN__is defined, but_WIN32is 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: | Microsoft |
| Distributions: | Windows XP, Vista, 7, 8 |
| Processors: | x86, x86-64 |
#if defined(_WIN64) /* Microsoft Windows (64-bit). ------------------------------ */ #elif defined(_WIN32) /* Microsoft Windows (32-bit). ------------------------------ */ #endif
| Macro | Clang/LLVM (Windows target) |
Clang/LLVM (MinGW target) |
GNU GCC/G++ (Windows target) |
GNU GCC/G++ (MinGW target) |
Intel ICC/ICPC |
Portland PGCC/PGCPP |
Microsoft Visual Studio |
||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 32-bit | 64-bit | 32-bit | 64-bit | 32-bit | 32-bit | 64-bit | 32-bit | 64-bit | 32-bit | 64-bit | 32-bit | 64-bit | |
__CYGWIN__ |
yes | ||||||||||||
__CYGWIN32__ |
yes | ||||||||||||
__MINGW32__ |
yes | yes | yes | yes | |||||||||
__MINGW64__ |
yes | yes | |||||||||||
unix |
yes | ||||||||||||
__unix |
yes | ||||||||||||
__unix__ |
yes | ||||||||||||
WIN32 |
yes | yes | yes | yes | |||||||||
_WIN32 |
yes | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes |
__WIN32 |
yes | yes | yes | yes | yes | yes | |||||||
__WIN32__ |
yes | yes | yes | yes | yes | yes | |||||||
WIN64 |
yes | yes | |||||||||||
_WIN64 |
yes | yes | yes | yes | yes | yes | |||||||
__WIN64 |
yes | yes | yes | ||||||||||
__WIN64__ |
yes | yes | yes | ||||||||||
WINNT |
yes | yes | yes | yes | |||||||||
__WINNT |
yes | yes | yes | ||||||||||
__WINNT__ |
yes | yes | yes | ||||||||||
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:
_WIN32and_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: | Standard |
| Distributions: | All current UNIX-style OSes, including BSD, Linux, OSX, and Solaris |
| Processors: | 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:
198808Lfor POSIX.1-1988199009Lfor POSIX.1-1990199506Lfor ISO POSIX.1-1996200112Lfor ISO POSIX.1-2001
The latest POSIX.1-2008 specification does not have a well-defined version number for the _POSIX_VERSION macro. However, some Linux distributions erroneously assign _POSIX_VERSION a value of200809L instead of leaving it at 200112L, as required by the POSIX specification.
From the POSIX specification, the preferred 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_IPV6indicates IPv6 address support._POSIX_MAPPED_FILESindicates memory mapping support._POSIX_SEMAPHORESindicates semaphore support for multi-threading._POSIX_THREADSindicates 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 standard |
| Distributions: | All current UNIX-style OSes, including BSD, Linux, OSX, and Solaris |
| Processors: | x86, x86-64, ARM, POWER, SPARC, etc. |
#if !defined(_WIN32) && (defined(__unix__) || defined(__unix) || (defined(__APPLE__) && defined(__MACH__))) /* UNIX-style OS. ------------------------------------------- */ #endif
| Macro | Cygwin (POSIX) | DragonFly BSD | FreeBSD | iOS | Linux | NetBSD | OpenBSD | OSX | Solaris |
|---|---|---|---|---|---|---|---|---|---|
unix |
yes | yes | yes | yes | yes | yes | |||
__unix |
yes | yes | yes | yes | yes | yes | |||
__unix__ |
yes | yes | yes | yes | yes | yes | yes |
| Macro | AIX | Cygwin (POSIX) | FreeBSD | iOS | HP-UX | Linux | NetBSD | OpenBSD | OSX | Solaris |
|---|---|---|---|---|---|---|---|---|---|---|
unix |
yes | yes | yes | yes | yes | |||||
__unix |
yes | yes | yes | yes | yes | |||||
__unix__ |
yes | yes | yes | yes | yes | yes | yes | yes |
| AIX | HP-UX | Linux | OSX | Solaris | |||||
|---|---|---|---|---|---|---|---|---|---|
| Macro | IBM XL C/C++ |
HP C/aC++ |
Intel ICC/ICPC |
Oracle Solaris Studio |
Portland PGCC/PGCPP |
IBM XL C/C++ |
Intel ICC/ICPC |
Portland PGCC/PGCPP |
Oracle Solaris Studio |
unix |
yes | yes | yes | yes | |||||
__unix |
yes | yes | yes | yes | yes | yes | yes | ||
__unix__ |
yes | yes | yes | yes | yes | ||||
Notes:
- There is no single UNIX macro defined by all compilers on all UNIX-style OSes. An
#if/#endifthat checks multiple macros is required. - Compilers for Apple's OSX and iOS don't define any UNIX macros. An
#if/#endifthat 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/#endifthat excludes_WIN32is 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 and winver 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/#endifsets for detecting common compilers. - C/C++ tip: How to detect the processor type using compiler predefined macros provides
#if/#endifsets 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.