iOS条件编译

在我们的工程中，很多时候只希望在满足一定条件的时候才进行编译，这是就需要用到条件编译。

#if #elif #else #endif

#if 条件1
    代码块1
#elif 条件2
    代码块2
...
#else  
    代码块n
#endif

用法举例
在开发中通常会在测试、线上等服务器间切换，我们可以写这样一个API的条件编译，根据情况使用条件控制不同的服务器API。

#if 0
#define  API_SEVER @"http://101.8.8.251:9000"         //本地test
#elif 1
#define  API_SEVER @"http://124.182.199.114:9000"     //线上test
#elif 0
#define  API_SEVER @"http://service1.com"             //正式1
#elif 0
#define  API_SEVER @"http://service2.com"             //正式2
#elif 0
#define  API_SEVER @""                                //备用
#endif

这只是一个简单的应用，还比如有时候我们在真机和模拟器上的编码并不是一样，利用条件编译就可以节省我们切换代码的工作。

#ifdef和#ifndef

#ifdef MACRO_Define  // 如果已定义MACRO_Define这个宏
    代码块1
#else
    代码块2
#endif

或

#ifndef MACRO_Define // 如果未定义MACRO_Define这个宏
    代码块1
#else
    代码块2
#endif

defined()函数
我们可以使用defined()和#if的组合，来代替上边的用法。使用defined()和#if的组合能判断更复杂的条件。

#if ( defined(MACRO_Define1) || (!defined(MACRO_Define2) && defined(MACRO_Define3) )
    代码块1
#else
    代码块2
#endif

补充

在系统库的的TargetConditionals.h文件中（我当前使用的iOS版本为9.3）


苹果已经定义了一些在不同编译器下的宏，这些宏我们在系统库的头文件或者其它地方我们会经常看到，在条件编译的时候我们也可以使用这些宏，大家可以了解一下。

  • 运行于Mac OS X的gcc编译器下
/*
 *    gcc based compiler used on Mac OS X
 */
#if defined(__GNUC__) && ( defined(__APPLE_CPP__) || defined(__APPLE_CC__) || defined(__MACOS_CLASSIC__) )
    #define TARGET_OS_MAC               1
    #define TARGET_OS_WIN32             0
    #define TARGET_OS_UNIX              0
    #define TARGET_OS_IPHONE            1 
    #define TARGET_OS_IOS               1
    #define TARGET_OS_WATCH             0
    #define TARGET_OS_TV                0
    #define TARGET_OS_SIMULATOR         1
    #define TARGET_OS_EMBEDDED          0 
    #define TARGET_IPHONE_SIMULATOR     TARGET_OS_SIMULATOR /* deprecated */
    #define TARGET_OS_NANO              TARGET_OS_WATCH /* deprecated */ 
    #if defined(__ppc__) 
        #define TARGET_CPU_PPC          1
        #define TARGET_CPU_PPC64        0
        #define TARGET_CPU_68K          0
        #define TARGET_CPU_X86          0
        #define TARGET_CPU_X86_64       0
        #define TARGET_CPU_ARM          0
        #define TARGET_CPU_ARM64        0
        #define TARGET_CPU_MIPS         0
        #define TARGET_CPU_SPARC        0   
        #define TARGET_CPU_ALPHA        0
        #define TARGET_RT_LITTLE_ENDIAN 0
        #define TARGET_RT_BIG_ENDIAN    1
        #define TARGET_RT_64_BIT        0
        #ifdef __MACOS_CLASSIC__
           #define TARGET_RT_MAC_CFM    1
           #define TARGET_RT_MAC_MACHO  0
        #else
           #define TARGET_RT_MAC_CFM    0
           #define TARGET_RT_MAC_MACHO  1
       #endif
    #elif defined(__ppc64__) 
        #define TARGET_CPU_PPC          0
        #define TARGET_CPU_PPC64        1
        #define TARGET_CPU_68K          0
        #define TARGET_CPU_X86          0
        #define TARGET_CPU_X86_64       0
        #define TARGET_CPU_ARM          0
        #define TARGET_CPU_ARM64        0
        #define TARGET_CPU_MIPS         0
        #define TARGET_CPU_SPARC        0   
        #define TARGET_CPU_ALPHA        0
        #define TARGET_RT_LITTLE_ENDIAN 0
        #define TARGET_RT_BIG_ENDIAN    1
        #define TARGET_RT_64_BIT        1
        #define TARGET_RT_MAC_CFM       0
        #define TARGET_RT_MAC_MACHO     1
    #elif defined(__i386__) 
        #define TARGET_CPU_PPC          0
        #define TARGET_CPU_PPC64        0
        #define TARGET_CPU_68K          0
        #define TARGET_CPU_X86          1
        #define TARGET_CPU_X86_64       0
        #define TARGET_CPU_ARM          0
        #define TARGET_CPU_ARM64        0
        #define TARGET_CPU_MIPS         0
        #define TARGET_CPU_SPARC        0
        #define TARGET_CPU_ALPHA        0
        #define TARGET_RT_MAC_CFM       0
        #define TARGET_RT_MAC_MACHO     1
        #define TARGET_RT_LITTLE_ENDIAN 1
        #define TARGET_RT_BIG_ENDIAN    0
        #define TARGET_RT_64_BIT        0
    #elif defined(__x86_64__) 
        #define TARGET_CPU_PPC          0
        #define TARGET_CPU_PPC64        0
        #define TARGET_CPU_68K          0
        #define TARGET_CPU_X86          0
        #define TARGET_CPU_X86_64       1
        #define TARGET_CPU_ARM          0
        #define TARGET_CPU_ARM64        0
        #define TARGET_CPU_MIPS         0
        #define TARGET_CPU_SPARC        0
        #define TARGET_CPU_ALPHA        0
        #define TARGET_RT_MAC_CFM       0
        #define TARGET_RT_MAC_MACHO     1
        #define TARGET_RT_LITTLE_ENDIAN 1
        #define TARGET_RT_BIG_ENDIAN    0
        #define TARGET_RT_64_BIT        1
    #elif defined(__arm__) 
        #define TARGET_CPU_PPC          0
        #define TARGET_CPU_PPC64        0
        #define TARGET_CPU_68K          0
        #define TARGET_CPU_X86          0
        #define TARGET_CPU_X86_64       0
        #define TARGET_CPU_ARM          1
        #define TARGET_CPU_ARM64        0
        #define TARGET_CPU_MIPS         0
        #define TARGET_CPU_SPARC        0
        #define TARGET_CPU_ALPHA        0
        #define TARGET_RT_MAC_CFM       0
        #define TARGET_RT_MAC_MACHO     1
        #define TARGET_RT_LITTLE_ENDIAN 1
        #define TARGET_RT_BIG_ENDIAN    0
        #define TARGET_RT_64_BIT        0
    #elif defined(__arm64__)
        #define TARGET_CPU_PPC          0
        #define TARGET_CPU_PPC64        0
        #define TARGET_CPU_68K          0
        #define TARGET_CPU_X86          0
        #define TARGET_CPU_X86_64       0
        #define TARGET_CPU_ARM          0
        #define TARGET_CPU_ARM64        1
        #define TARGET_CPU_MIPS         0
        #define TARGET_CPU_SPARC        0
        #define TARGET_CPU_ALPHA        0
        #define TARGET_RT_MAC_CFM       0
        #define TARGET_RT_MAC_MACHO     1
        #define TARGET_RT_LITTLE_ENDIAN 1
        #define TARGET_RT_BIG_ENDIAN    0
        #define TARGET_RT_64_BIT        1
    #else
        #error unrecognized GNU C compiler
    #endif
  • 来自于Metrowerks/Motorola的CodeWarrior编译器
/*
 *   CodeWarrior compiler from Metrowerks/Motorola
 */
#elif defined(__MWERKS__)
    #define TARGET_OS_MAC               1
    #define TARGET_OS_WIN32             0
    #define TARGET_OS_UNIX              0
    #define TARGET_OS_EMBEDDED          0
    #if defined(__POWERPC__)
        #define TARGET_CPU_PPC          1
        #define TARGET_CPU_PPC64        0
        #define TARGET_CPU_68K          0
        #define TARGET_CPU_X86          0
        #define TARGET_CPU_MIPS         0
        #define TARGET_CPU_SPARC        0
        #define TARGET_CPU_ALPHA        0
        #define TARGET_RT_LITTLE_ENDIAN 0
        #define TARGET_RT_BIG_ENDIAN    1
    #elif defined(__INTEL__)
        #define TARGET_CPU_PPC          0
        #define TARGET_CPU_PPC64        0
        #define TARGET_CPU_68K          0
        #define TARGET_CPU_X86          1
        #define TARGET_CPU_MIPS         0
        #define TARGET_CPU_SPARC        0
        #define TARGET_CPU_ALPHA        0
        #define TARGET_RT_LITTLE_ENDIAN 1
        #define TARGET_RT_BIG_ENDIAN    0
    #else
        #error unknown Metrowerks CPU type
    #endif
    #define TARGET_RT_64_BIT            0
    #ifdef __MACH__
        #define TARGET_RT_MAC_CFM       0
        #define TARGET_RT_MAC_MACHO     1
    #else
        #define TARGET_RT_MAC_CFM       1
        #define TARGET_RT_MAC_MACHO     0
    #endif
  • 未知编译器
/*
 *   unknown compiler
 */
#else
    #if defined(TARGET_CPU_PPC) && TARGET_CPU_PPC
        #define TARGET_CPU_PPC64    0
        #define TARGET_CPU_68K      0
        #define TARGET_CPU_X86      0
        #define TARGET_CPU_X86_64   0
        #define TARGET_CPU_ARM      0
        #define TARGET_CPU_ARM64    0
        #define TARGET_CPU_MIPS     0
        #define TARGET_CPU_SPARC    0
        #define TARGET_CPU_ALPHA    0
    #elif defined(TARGET_CPU_PPC64) && TARGET_CPU_PPC64
        #define TARGET_CPU_PPC      0
        #define TARGET_CPU_68K      0
        #define TARGET_CPU_X86      0
        #define TARGET_CPU_X86_64   0
        #define TARGET_CPU_ARM      0
        #define TARGET_CPU_ARM64    0
        #define TARGET_CPU_MIPS     0
        #define TARGET_CPU_SPARC    0
        #define TARGET_CPU_ALPHA    0
    #elif defined(TARGET_CPU_X86) && TARGET_CPU_X86
        #define TARGET_CPU_PPC      0
        #define TARGET_CPU_PPC64    0
        #define TARGET_CPU_X86_64   0
        #define TARGET_CPU_68K      0
        #define TARGET_CPU_ARM      0
        #define TARGET_CPU_ARM64    0
        #define TARGET_CPU_MIPS     0
        #define TARGET_CPU_SPARC    0
        #define TARGET_CPU_ALPHA    0
    #elif defined(TARGET_CPU_X86_64) && TARGET_CPU_X86_64
        #define TARGET_CPU_PPC      0
        #define TARGET_CPU_PPC64    0
        #define TARGET_CPU_X86      0
        #define TARGET_CPU_68K      0
        #define TARGET_CPU_ARM      0
        #define TARGET_CPU_ARM64    0
        #define TARGET_CPU_MIPS     0
        #define TARGET_CPU_SPARC    0
        #define TARGET_CPU_ALPHA    0
    #elif defined(TARGET_CPU_ARM) && TARGET_CPU_ARM
        #define TARGET_CPU_PPC      0
        #define TARGET_CPU_PPC64    0
        #define TARGET_CPU_X86      0
        #define TARGET_CPU_X86_64   0
        #define TARGET_CPU_68K      0
        #define TARGET_CPU_ARM64    0
        #define TARGET_CPU_MIPS     0
        #define TARGET_CPU_SPARC    0
        #define TARGET_CPU_ALPHA    0
    #elif defined(TARGET_CPU_ARM64) && TARGET_CPU_ARM64
        #define TARGET_CPU_PPC      0
        #define TARGET_CPU_PPC64    0
        #define TARGET_CPU_X86      0
        #define TARGET_CPU_X86_64   0
        #define TARGET_CPU_68K      0
        #define TARGET_CPU_ARM      0
        #define TARGET_CPU_MIPS     0
        #define TARGET_CPU_SPARC    0
        #define TARGET_CPU_ALPHA    0
    #else
        /*
            NOTE:   If your compiler errors out here then support for your compiler 
            has not yet been added to TargetConditionals.h.  
            
            TargetConditionals.h is designed to be plug-and-play.  It auto detects
            which compiler is being run and configures the TARGET_ conditionals
            appropriately.  
            
            The short term work around is to set the TARGET_CPU_ and TARGET_OS_
            on the command line to the compiler (e.g. -DTARGET_CPU_MIPS=1 -DTARGET_OS_UNIX=1)
            
            The long term solution is to add a new case to this file which
            auto detects your compiler and sets up the TARGET_ conditionals.
            Then submit the changes to Apple Computer.
        */
        #error TargetConditionals.h: unknown compiler (see comment above)
        #define TARGET_CPU_PPC    0
        #define TARGET_CPU_68K    0
        #define TARGET_CPU_X86    0
        #define TARGET_CPU_ARM    0
        #define TARGET_CPU_ARM64  0
        #define TARGET_CPU_MIPS   0
        #define TARGET_CPU_SPARC  0
        #define TARGET_CPU_ALPHA  0
    #endif
    #define TARGET_OS_MAC                1
    #define TARGET_OS_WIN32              0
    #define TARGET_OS_UNIX               0
    #define TARGET_OS_EMBEDDED           0
    #if TARGET_CPU_PPC || TARGET_CPU_PPC64
        #define TARGET_RT_BIG_ENDIAN     1
        #define TARGET_RT_LITTLE_ENDIAN  0
    #else
        #define TARGET_RT_BIG_ENDIAN     0
        #define TARGET_RT_LITTLE_ENDIAN  1
    #endif
    #if TARGET_CPU_PPC64 || TARGET_CPU_X86_64
        #define TARGET_RT_64_BIT         1
    #else
        #define TARGET_RT_64_BIT         0
    #endif
    #ifdef __MACH__
        #define TARGET_RT_MAC_MACHO      1
        #define TARGET_RT_MAC_CFM        0
    #else
        #define TARGET_RT_MAC_MACHO      0
        #define TARGET_RT_MAC_CFM        1
    #endif
#endif

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