C⼀C++是怎么通过宏定义来判断操作系统的

详见Qt的qglobal.h
我们写C/C++代码时也可以参考这个来确定所在平台

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/*
The operating system, must be one of: (Q_OS_x)

DARWIN - Darwin OS (synonym for Q_OS_MAC)
SYMBIAN - Symbian
MSDOS - MS-DOS and Windows
OS2 - OS/2
OS2EMX - XFree86 on OS/2 (not PM)
WIN32 - Win32 (Windows 2000/XP/Vista/7 and Windows Server 2003/2008)
WINCE - WinCE (Windows CE 5.0)
CYGWIN - Cygwin
SOLARIS - Sun Solaris
HPUX - HP-UX
ULTRIX - DEC Ultrix
LINUX - Linux
FREEBSD - FreeBSD
NETBSD - NetBSD
OPENBSD - OpenBSD
BSDI - BSD/OS
IRIX - SGI Irix
OSF - HP Tru64 UNIX
SCO - SCO OpenServer 5
UNIXWARE - UnixWare 7, Open UNIX 8
AIX - AIX
HURD - GNU Hurd
DGUX - DG/UX
RELIANT - Reliant UNIX
DYNIX - DYNIX/ptx
QNX - QNX
LYNX - LynxOS
BSD4 - Any BSD 4.4 system
UNIX - Any UNIX BSD/SYSV system
*/

#if defined(__APPLE__) && (defined(__GNUC__) || defined(__xlC__) || defined(__xlc__))
# define Q_OS_DARWIN
# define Q_OS_BSD4
# ifdef __LP64__
# define Q_OS_DARWIN64
# else
# define Q_OS_DARWIN32
# endif
#elif defined(__SYMBIAN32__) || defined(SYMBIAN)
# define Q_OS_SYMBIAN
# define Q_NO_POSIX_SIGNALS
# define QT_NO_GETIFADDRS
#elif defined(__CYGWIN__)
# define Q_OS_CYGWIN
#elif defined(MSDOS) || defined(_MSDOS)
# define Q_OS_MSDOS
#elif defined(__OS2__)
# if defined(__EMX__)
# define Q_OS_OS2EMX
# else
# define Q_OS_OS2
# endif
#elif !defined(SAG_COM) && (defined(WIN64) || defined(_WIN64) || defined(__WIN64__))
# define Q_OS_WIN32
# define Q_OS_WIN64
#elif !defined(SAG_COM) && (defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__NT__))
# if defined(WINCE) || defined(_WIN32_WCE)
# define Q_OS_WINCE
# else
# define Q_OS_WIN32
# endif
#elif defined(__MWERKS__) && defined(__INTEL__)
# define Q_OS_WIN32
#elif defined(__sun) || defined(sun)
# define Q_OS_SOLARIS
#elif defined(hpux) || defined(__hpux)
# define Q_OS_HPUX
#elif defined(__ultrix) || defined(ultrix)
# define Q_OS_ULTRIX
#elif defined(sinix)
# define Q_OS_RELIANT
#elif defined(__native_client__)
# define Q_OS_NACL
#elif defined(__linux__) || defined(__linux)
# define Q_OS_LINUX
#elif defined(__FreeBSD__) || defined(__DragonFly__)
# define Q_OS_FREEBSD
# define Q_OS_BSD4
#elif defined(__NetBSD__)
# define Q_OS_NETBSD
# define Q_OS_BSD4
#elif defined(__OpenBSD__)
# define Q_OS_OPENBSD
# define Q_OS_BSD4
#elif defined(__bsdi__)
# define Q_OS_BSDI
# define Q_OS_BSD4
#elif defined(__sgi)
# define Q_OS_IRIX
#elif defined(__osf__)
# define Q_OS_OSF
#elif defined(_AIX)
# define Q_OS_AIX
#elif defined(__Lynx__)
# define Q_OS_LYNX
#elif defined(__GNU__)
# define Q_OS_HURD
#elif defined(__DGUX__)
# define Q_OS_DGUX
#elif defined(__QNXNTO__)
# define Q_OS_QNX
#elif defined(_SEQUENT_)
# define Q_OS_DYNIX
#elif defined(_SCO_DS) /* SCO OpenServer 5 + GCC */
# define Q_OS_SCO
#elif defined(__USLC__) /* all SCO platforms + UDK or OUDK */
# define Q_OS_UNIXWARE
#elif defined(__svr4__) && defined(i386) /* Open UNIX 8 + GCC */
# define Q_OS_UNIXWARE
#elif defined(__INTEGRITY)
# define Q_OS_INTEGRITY
#elif defined(VXWORKS) /* there is no "real" VxWorks define - this has to be set in the mkspec! */
# define Q_OS_VXWORKS
#elif defined(__MAKEDEPEND__)
#else
# error "Qt has not been ported to this OS - talk to qt-bugs@trolltech.com"
#endif

#if defined(Q_OS_WIN32) || defined(Q_OS_WIN64) || defined(Q_OS_WINCE)
# define Q_OS_WIN
#endif

#if defined(Q_OS_DARWIN)
# define Q_OS_MAC /* Q_OS_MAC is mostly for compatibility, but also more clear */
# define Q_OS_MACX /* Q_OS_MACX is only for compatibility.*/
# if defined(Q_OS_DARWIN64)
# define Q_OS_MAC64
# elif defined(Q_OS_DARWIN32)
# define Q_OS_MAC32
# endif
#endif