About c++ : Which-macro-to-wrap-Mac-OS-X-specific-code-in-CC

While reading various C and C++ sources, I have encountered two macros __APPLE__ and __OSX__. I found plenty of use of __OSX__ in various codes, especially those originating from *BSD systems.

However, sometimes I find that testing __OSX__ only is not sufficient and I have to complete tests with __APPLE__ macro.

The Porting Command Line Unix Tools to Mac OS X guides specifies __APPLE__ and additionally __APPLE_CC__ but does not mention __OSX__.

The Porting from GCC guide says:

• Use #ifdef __GNUC__ to wrap any GCC-specific code.
• Use #ifdef __APPLE_CC__ to wrap any Mac OS X-specific code.

Again, no mention about __OSX__ macro.

What macro is predefined on Mac OS X platform and XCode development environment that should be used to distinguish OSX-specific code in C/C++ programs?

Where is the __OSX__ macro defined? Is it *BSD specific macro?

It all depends.

Each macro specifies something different in meaning.
See: https://developer.apple.com/library/mac/documentation/Porting/Conceptual/PortingUnix/compiling/compiling.html#//apple_ref/doc/uid/TP40002850-SW13

__APPLE__

This macro is defined in any Apple computer.

__APPLE_CC__

This macro is set to an integer that represents the version number of
the compiler. This lets you distinguish, for example, between compilers
based on the same version of GCC, but with different bug fixes or features.
Larger values denote later compilers.

__OSX__

Presumably the OS is a particular variant of OS X

So given the above definitions I would use __APPLE__ to distinguish apple specific code.

Here is a nice list of macros for operating systems.

There’s little info on __OSX__ on the web. You’ll be safe with __APPLE__.

I normally use __MACH__ for this. It’s been defined since the earliest version of OS X (and even before, presumably).

If you want to exclude the possibility that you might be compiling for some other OS that uses the Mach kernel then you can use @scravy’s suggestion of:

#if defined(__APPLE__) && defined(__MACH__)

Note also that if you’re compiling generic C/C++ code, i.e. no Apple-speacific headers, so you are just interested in pre-defined compiler macros, you can check these as follows:

$ gcc -dM -E - < /dev/null | egrep -i 'os_|mac|apple'
#define __APPLE_CC__ 6000
#define __APPLE__ 1
#define __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ 120000
#define __ENVIRONMENT_OS_VERSION_MIN_REQUIRED__ 120000
#define __MACH__ 1
#define __VERSION__ "Apple LLVM 13.1.6 (clang-1316.0.21.2.3)"
#define __apple_build_version__ 13160021

Use

#if defined(__APPLE__) && defined(__MACH__)

to distinguish Apple operating systems.

You can further use TARGET_OS_MAC and TARGET_OS_IPHONE to distinguish between macOS and iOS.

Full example:

#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 */

#elif TARGET_OS_MAC == 1
    /* macOS */

#endif
#endif

Regarding the question of “where does __OSX__ come from?”:

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.

Source: http://nadeausoftware.com/articles/2012/01/c_c_tip_how_use_compiler_predefined_macros_detect_operating_system

Update – the above link is broken, see version in web archive: https://web.archive.org/web/20180331065236/http://nadeausoftware.com/articles/2012/01/c_c_tip_how_use_compiler_predefined_macros_detect_operating_system#OSXiOSandDarwin

For anyone coming across this question >= 2019, I found there’s a header “Availability.h”.

In that header, are #defines like:

#define __MAC_10_0            1000
#define __MAC_10_1            1010
#define __MAC_10_2            1020
#define __MAC_10_3            1030
#define __MAC_10_4            1040
#define __MAC_10_5            1050
#define __MAC_10_6            1060
#define __MAC_10_7            1070
#define __MAC_10_8            1080
#define __MAC_10_9            1090
#define __MAC_10_10         101000
#define __MAC_10_10_2       101002
#define __MAC_10_10_3       101003
#define __MAC_10_11         101100
#define __MAC_10_11_2       101102

So you CAN tell if you’re compiling on a particular MacOS platform.

See http://nadeausoftware.com/articles/2012/01/c_c_tip_how_use_compiler_predefined_macros_detect_operating_system#OSXiOSandDarwin

#ifdef __APPLE__
#include <TargetConditionals.h>
#if TARGET_OS_MAC
   ...
#endif /* TARGET_OS_MAC */
#endif /* __APPLE__ */

Note that __OSX__ does NOT exist, at least as of Xcode 9.

Also note that it is #if TARGET_OS_MAC not #ifdef. It is always defined, but is 0 when not macOS.