在編寫跨平臺的程式碼時，我們往往需要用到條件編譯的巨集，以便讓同一套程式碼相容編譯器不同版本、不同作業系統，下面就介紹下這些巨集。

區分編譯器不同版本的巨集

每個編譯器都會自帶一些預定義巨集，以下拿gcc和VC++舉例：

在編譯器眾多的預定義巨集中，肯定有一個是用於標識編譯器版本的巨集定義：

• GCC編譯器：__GNUC__
• Visual C++編譯器：_MSC_VER

__GNUC__是用來定義gcc編譯器的版本，我們可以使用如下程式碼來進行條件編譯：

/* Test for GCC > 3.2.0 */
#if __GNUC__ > 3 || \
    (__GNUC__ == 3 && (__GNUC_MINOR__ > 2 || \
                       (__GNUC_MINOR__ == 2 && \
                        __GNUC_PATCHLEVEL__ > 0))

Another approach is to use the predefined macros to calculate a single number, then compare that against a threshold:

#define GCC_VERSION (__GNUC__ * 10000 \
                     + __GNUC_MINOR__ * 100 \
                     + __GNUC_PATCHLEVEL__)

/* Test for GCC > 3.2.0 */
#if GCC_VERSION > 30200
 

_MSC_VER是微軟公司推出的C/C++編譯器在ANSI/ISO C99標準之外擴充套件的巨集定義，用來定義當前微軟公司自己的編譯器的主版本。下面是一些編譯器版本的_MSC_VER值：

MSVC++ 14.1 _MSC_VER == 1910 (Visual Studio 2017)
MSVC++ 14.0 _MSC_VER == 1900 (Visual Studio 2015)
MSVC++ 12.0 _MSC_VER == 1800 (Visual Studio 2013)
MSVC++ 11.0 _MSC_VER == 1700 (Visual Studio 2012)
MSVC++ 10.0 _MSC_VER == 1600 (Visual Studio 2010)
MSVC++ 9.0  _MSC_VER == 1500 (Visual Studio 2008)
MSVC++ 8.0  _MSC_VER == 1400 (Visual Studio 2005)
MSVC++ 7.1  _MSC_VER == 1310 (Visual Studio 2003)
MSVC++ 7.0  _MSC_VER == 1300
MSVC++ 6.0  _MSC_VER == 1200
MSVC++ 5.0  _MSC_VER == 1100
 

其中MS VC++ 14.0表示Visual C++的版本為14.0，後面括號中的Visual Studio 2015，表明該VC++包含在微軟開發工具Visual Studio 2015中。

/* Test for MSVC++ > Microsoft Visual Studio 2010 */
#if _MSC_VER > 1600

區分不同作業系統的巨集

可以參考QtCore/qsystemdetection.h檔案：

    #ifndef QSYSTEMDETECTION_H
    #define QSYSTEMDETECTION_H

    /*
       The operating system, must be one of: (Q_OS_x)
         DARWIN   - Any Darwin system
         MAC      - OS X and iOS
         OSX      - OS X
         IOS      - iOS
         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)
         WINRT    - WinRT (Windows 8 Runtime)
         CYGWIN   - Cygwin
         SOLARIS  - Sun Solaris
         HPUX     - HP-UX
         ULTRIX   - DEC Ultrix
         LINUX    - Linux [has variants]
         FREEBSD  - FreeBSD [has variants]
         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 [has variants]
         QNX6     - QNX RTP 6.1
         LYNX     - LynxOS
         BSD4     - Any BSD 4.4 system
         UNIX     - Any UNIX BSD/SYSV system
         ANDROID  - Android platform
         HAIKU    - Haiku
       The following operating systems have variants:
         LINUX    - both Q_OS_LINUX and Q_OS_ANDROID are defined when building for Android
                  - only Q_OS_LINUX is defined if building for other Linux systems
         QNX      - both Q_OS_QNX and Q_OS_BLACKBERRY are defined when building for Blackberry 10
                  - only Q_OS_QNX is defined if building for other QNX targets
         FREEBSD  - Q_OS_FREEBSD is defined only when building for FreeBSD with a BSD userland
                  - Q_OS_FREEBSD_KERNEL is always defined on FreeBSD, even if the userland is from GNU
    */
 


    #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(ANDROID)
    #  define Q_OS_ANDROID
    #  define Q_OS_LINUX
    #elif defined(__CYGWIN__)
    #  define Q_OS_CYGWIN
    #elif !defined(SAG_COM) && (!defined(WINAPI_FAMILY) || WINAPI_FAMILY==WINAPI_FAMILY_DESKTOP_APP) && (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
    #  elif defined(WINAPI_FAMILY)
    #    if defined(WINAPI_FAMILY_PHONE_APP) && WINAPI_FAMILY==WINAPI_FAMILY_PHONE_APP
    #      define Q_OS_WINPHONE
    #      define Q_OS_WINRT
    #    elif WINAPI_FAMILY==WINAPI_FAMILY_APP
    #      define Q_OS_WINRT
    #    else
    #      define Q_OS_WIN32
    #    endif
    #  else
    #    define Q_OS_WIN32
    #  endif
    #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__) || defined(__FreeBSD_kernel__)
    #  ifndef __FreeBSD_kernel__
    #    define Q_OS_FREEBSD
    #  endif
    #  define Q_OS_FREEBSD_KERNEL
    #  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(__HAIKU__)
    #  define Q_OS_HAIKU
    #elif defined(__MAKEDEPEND__)
    #else
    #  error "Qt has not been ported to this OS - see http://www.qt-project.org/"
    #endif

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

    #if defined(Q_OS_DARWIN)
    #  define Q_OS_MAC
    #  if defined(Q_OS_DARWIN64)
    #     define Q_OS_MAC64
    #  elif defined(Q_OS_DARWIN32)
    #     define Q_OS_MAC32
    #  endif
    #  include <TargetConditionals.h>
    #  if defined(TARGET_OS_IPHONE) && TARGET_OS_IPHONE
    #     define Q_OS_IOS
    #  elif defined(TARGET_OS_MAC) && TARGET_OS_MAC
    #     define Q_OS_OSX
    #     define Q_OS_MACX // compatibility synonym
    #  endif
    #endif

    #if defined(Q_OS_WIN)
    #  undef Q_OS_UNIX
    #elif !defined(Q_OS_UNIX)
    #  define Q_OS_UNIX
    #endif

    #ifdef Q_OS_DARWIN
    #  include <Availability.h>
    #  include <AvailabilityMacros.h>
    #
    #  ifdef Q_OS_OSX
    #    if !defined(__MAC_OS_X_VERSION_MIN_REQUIRED) || __MAC_OS_X_VERSION_MIN_REQUIRED < __MAC_10_6
    #       undef __MAC_OS_X_VERSION_MIN_REQUIRED
    #       define __MAC_OS_X_VERSION_MIN_REQUIRED __MAC_10_6
    #    endif
    #    if !defined(MAC_OS_X_VERSION_MIN_REQUIRED) || MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_6
    #       undef MAC_OS_X_VERSION_MIN_REQUIRED
    #       define MAC_OS_X_VERSION_MIN_REQUIRED MAC_OS_X_VERSION_10_6
    #    endif
    #  endif
    #
    #  // Numerical checks are preferred to named checks, but to be safe
    #  // we define the missing version names in case Qt uses them.
    #
    #  if !defined(__MAC_10_7)
    #       define __MAC_10_7 1070
    #  endif
    #  if !defined(__MAC_10_8)
    #       define __MAC_10_8 1080
    #  endif
    #  if !defined(__MAC_10_9)
    #       define __MAC_10_9 1090
    #  endif
    #  if !defined(__MAC_10_10)
    #       define __MAC_10_10 101000
    #  endif
    #  if !defined(__MAC_10_11)
    #       define __MAC_10_11 101100
    #  endif
    #  if !defined(MAC_OS_X_VERSION_10_7)
    #       define MAC_OS_X_VERSION_10_7 1070
    #  endif
    #  if !defined(MAC_OS_X_VERSION_10_8)
    #       define MAC_OS_X_VERSION_10_8 1080
    #  endif
    #  if !defined(MAC_OS_X_VERSION_10_9)
    #       define MAC_OS_X_VERSION_10_9 1090
    #  endif
    #  if !defined(MAC_OS_X_VERSION_10_10)
    #       define MAC_OS_X_VERSION_10_10 101000
    #  endif
    #  if !defined(MAC_OS_X_VERSION_10_11)
    #       define MAC_OS_X_VERSION_10_11 101100
    #  endif
    #
    #  if !defined(__IPHONE_4_3)
    #       define __IPHONE_4_3 40300
    #  endif
    #  if !defined(__IPHONE_5_0)
    #       define __IPHONE_5_0 50000
    #  endif
    #  if !defined(__IPHONE_5_1)
    #       define __IPHONE_5_1 50100
    #  endif
    #  if !defined(__IPHONE_6_0)
    #       define __IPHONE_6_0 60000
    #  endif
    #  if !defined(__IPHONE_6_1)
    #       define __IPHONE_6_1 60100
    #  endif
    #  if !defined(__IPHONE_7_0)
    #       define __IPHONE_7_0 70000
    #  endif
    #  if !defined(__IPHONE_7_1)
    #       define __IPHONE_7_1 70100
    #  endif
    #  if !defined(__IPHONE_8_0)
    #       define __IPHONE_8_0 80000
    #  endif
    #  if !defined(__IPHONE_8_1)
    #       define __IPHONE_8_1 80100
    #  endif
    #  if !defined(__IPHONE_8_2)
    #       define __IPHONE_8_2 80200
    #  endif
    #  if !defined(__IPHONE_8_3)
    #       define __IPHONE_8_3 80300
    #  endif
    #  if !defined(__IPHONE_8_4)
    #       define __IPHONE_8_4 80400
    #  endif
    #  if !defined(__IPHONE_9_0)
    #       define __IPHONE_9_0 90000
    #  endif
    #endif

    #ifdef __LSB_VERSION__
    #  if __LSB_VERSION__ < 40
    #    error "This version of the Linux Standard Base is unsupported"
    #  endif
    #ifndef QT_LINUXBASE
    #  define QT_LINUXBASE
    #endif
    #endif

    #endif // QSYSTEMDETECTION_H