检测 <Secure/SecRandom.h> 的可用性？
Detect availability of <Secure/SecRandom.h>?
我正在使用 cross-platform C++ 库。虽然该库试图成为不可知论者，但它确实有时会与 Cocoa/CocoaTouch 安全框架等框架集成。
在现代达尔文系统上，如 OS X 107、10.8 和 10.9（以及 iOS 等价物），以下工作正常。现代系统使用 Xcode 4.3 及更高版本。
#include <Secure/SecRandom.h>
在较旧的 PowerMac 运行 OS X 10.5 和 Xcode 3.1 上，包含导致 compile error。较旧的 PowerMac 仍然可以进行测试，因为它是 big-endian、PowerPC cpu.
$ make
...
/opt/local/bin/clang++-mp-3.4 -m64 -pthread -stdlib=libc++ -fPIC -fvisibility=hidden
-std=c++11 -D_REENTRANT -fstack-protector -O3 -Wall -Wextra -Ibuild/include
-c ./src/lib/entropy/darwin_secrandom/darwin_secrandom.cpp -o build/obj/lib/entropy_darwin_secrandom.o
./src/lib/entropy/darwin_secrandom/darwin_secrandom.cpp:10:10: fatal error:
'Security/SecRandom.h' file not found
#include <Security/SecRandom.h>
^
1 error generated.
make: *** [build/obj/lib/entropy_darwin_secrandom.o] Error 1
我的问题是，我们如何判断 <Security/SecRandom.h> 何时可用？它与 Xcode 4 及更高版本相关吗？或者它与其他东西有关？如果是这样，我们使用什么预处理器宏来检测可用性？
当我查看预处理器宏时，我没有看到用于向用户发出信号的内容。显然，MacPorts 编译器正在与 Cocoa 和 CocoaTouch 等框架集成（或了解），因为我们可以包含 headers，例如 TargetConditionals.h:
$ /opt/local/bin/clang++-mp-3.4 -m64 -pthread -stdlib=libc++ -fPIC -include TargetConditionals.h -x c++ -dM -E - < /dev/null | sort
#define OBJC_NEW_PROPERTIES 1
#define TARGET_CPU_68K 0
#define TARGET_CPU_ALPHA 0
#define TARGET_CPU_MIPS 0
#define TARGET_CPU_PPC 1
#define TARGET_CPU_PPC64 0
#define TARGET_CPU_SPARC 0
#define TARGET_CPU_X86 0
#define TARGET_CPU_X86_64 0
#define TARGET_OS_EMBEDDED 0
#define TARGET_OS_MAC 1
#define TARGET_OS_UNIX 0
#define TARGET_OS_WIN32 0
#define TARGET_RT_64_BIT 0
#define TARGET_RT_BIG_ENDIAN 1
#define TARGET_RT_LITTLE_ENDIAN 0
#define TARGET_RT_MAC_CFM 0
#define TARGET_RT_MAC_MACHO 1
#define _ARCH_PPC 1
#define _ARCH_PPC64 1
#define _BIG_ENDIAN 1
#define _LP64 1
#define _REENTRANT 1
#define __APPLE_CC__ 6000
#define __APPLE__ 1
#define __ATOMIC_ACQUIRE 2
#define __ATOMIC_ACQ_REL 4
#define __ATOMIC_CONSUME 1
#define __ATOMIC_RELAXED 0
#define __ATOMIC_RELEASE 3
#define __ATOMIC_SEQ_CST 5
#define __BIG_ENDIAN__ 1
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
#define __CHAR16_TYPE__ unsigned short
#define __CHAR32_TYPE__ unsigned int
#define __CHAR_BIT__ 8
#define __CONSTANT_CFSTRINGS__ 1
#define __DBL_DENORM_MIN__ 4.9406564584124654e-324
#define __DBL_DIG__ 15
#define __DBL_EPSILON__ 2.2204460492503131e-16
#define __DBL_HAS_DENORM__ 1
#define __DBL_HAS_INFINITY__ 1
#define __DBL_HAS_QUIET_NAN__ 1
#define __DBL_MANT_DIG__ 53
#define __DBL_MAX_10_EXP__ 308
#define __DBL_MAX_EXP__ 1024
#define __DBL_MAX__ 1.7976931348623157e+308
#define __DBL_MIN_10_EXP__ (-307)
#define __DBL_MIN_EXP__ (-1021)
#define __DBL_MIN__ 2.2250738585072014e-308
#define __DECIMAL_DIG__ 33
#define __DEPRECATED 1
#define __DYNAMIC__ 1
#define __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ 1050
#define __EXCEPTIONS 1
#define __FINITE_MATH_ONLY__ 0
#define __FLT_DENORM_MIN__ 1.40129846e-45F
#define __FLT_DIG__ 6
#define __FLT_EPSILON__ 1.19209290e-7F
#define __FLT_EVAL_METHOD__ 0
#define __FLT_HAS_DENORM__ 1
#define __FLT_HAS_INFINITY__ 1
#define __FLT_HAS_QUIET_NAN__ 1
#define __FLT_MANT_DIG__ 24
#define __FLT_MAX_10_EXP__ 38
#define __FLT_MAX_EXP__ 128
#define __FLT_MAX__ 3.40282347e+38F
#define __FLT_MIN_10_EXP__ (-37)
#define __FLT_MIN_EXP__ (-125)
#define __FLT_MIN__ 1.17549435e-38F
#define __FLT_RADIX__ 2
#define __GCC_ATOMIC_BOOL_LOCK_FREE 2
#define __GCC_ATOMIC_CHAR16_T_LOCK_FREE 2
#define __GCC_ATOMIC_CHAR32_T_LOCK_FREE 2
#define __GCC_ATOMIC_CHAR_LOCK_FREE 2
#define __GCC_ATOMIC_INT_LOCK_FREE 2
#define __GCC_ATOMIC_LLONG_LOCK_FREE 2
#define __GCC_ATOMIC_LONG_LOCK_FREE 2
#define __GCC_ATOMIC_POINTER_LOCK_FREE 2
#define __GCC_ATOMIC_SHORT_LOCK_FREE 2
#define __GCC_ATOMIC_TEST_AND_SET_TRUEVAL 1
#define __GCC_ATOMIC_WCHAR_T_LOCK_FREE 2
#define __GNUC_GNU_INLINE__ 1
#define __GNUC_MINOR__ 2
#define __GNUC_PATCHLEVEL__ 1
#define __GNUC__ 4
#define __GNUG__ 4
#define __GXX_ABI_VERSION 1002
#define __GXX_RTTI 1
#define __GXX_WEAK__ 1
#define __INT16_TYPE__ short
#define __INT32_TYPE__ int
#define __INT64_C_SUFFIX__ L
#define __INT64_TYPE__ long int
#define __INT8_TYPE__ char
#define __INTMAX_MAX__ 9223372036854775807L
#define __INTMAX_TYPE__ long int
#define __INTMAX_WIDTH__ 64
#define __INTPTR_TYPE__ long int
#define __INTPTR_WIDTH__ 64
#define __INT_MAX__ 2147483647
#define __LDBL_DENORM_MIN__ 4.94065645841246544176568792868221e-324L
#define __LDBL_DIG__ 31
#define __LDBL_EPSILON__ 4.94065645841246544176568792868221e-324L
#define __LDBL_HAS_DENORM__ 1
#define __LDBL_HAS_INFINITY__ 1
#define __LDBL_HAS_QUIET_NAN__ 1
#define __LDBL_MANT_DIG__ 106
#define __LDBL_MAX_10_EXP__ 308
#define __LDBL_MAX_EXP__ 1024
#define __LDBL_MAX__ 1.79769313486231580793728971405301e+308L
#define __LDBL_MIN_10_EXP__ (-291)
#define __LDBL_MIN_EXP__ (-968)
#define __LDBL_MIN__ 2.00416836000897277799610805135016e-292L
#define __LONG_DOUBLE_128__ 1
#define __LONG_LONG_MAX__ 9223372036854775807LL
#define __LONG_MAX__ 9223372036854775807L
#define __LP64__ 1
#define __MACH__ 1
#define __NATURAL_ALIGNMENT__ 1
#define __NO_INLINE__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
#define __PIC__ 2
#define __POINTER_WIDTH__ 64
#define __POWERPC__ 1
#define __PPC64__ 1
#define __PPC__ 1
#define __PRAGMA_REDEFINE_EXTNAME 1
#define __PTRDIFF_TYPE__ long int
#define __PTRDIFF_WIDTH__ 64
#define __REGISTER_PREFIX__
#define __SCHAR_MAX__ 127
#define __SHRT_MAX__ 32767
#define __SIG_ATOMIC_WIDTH__ 32
#define __SIZEOF_DOUBLE__ 8
#define __SIZEOF_FLOAT__ 4
#define __SIZEOF_INT128__ 16
#define __SIZEOF_INT__ 4
#define __SIZEOF_LONG_DOUBLE__ 16
#define __SIZEOF_LONG_LONG__ 8
#define __SIZEOF_LONG__ 8
#define __SIZEOF_POINTER__ 8
#define __SIZEOF_PTRDIFF_T__ 8
#define __SIZEOF_SHORT__ 2
#define __SIZEOF_SIZE_T__ 8
#define __SIZEOF_WCHAR_T__ 4
#define __SIZEOF_WINT_T__ 4
#define __SIZE_MAX__ 18446744073709551615UL
#define __SIZE_TYPE__ long unsigned int
#define __SIZE_WIDTH__ 64
#define __STDC_HOSTED__ 1
#define __STDC_UTF_16__ 1
#define __STDC_UTF_32__ 1
#define __STDC__ 1
#define __TARGETCONDITIONALS__
#define __UINTMAX_TYPE__ long unsigned int
#define __USER_LABEL_PREFIX__ _
#define __VERSION__ "4.2.1 Compatible Clang 3.4.2 (tags/RELEASE_34/dot2-final)"
#define __WCHAR_MAX__ 2147483647
#define __WCHAR_TYPE__ int
#define __WCHAR_WIDTH__ 32
#define __WINT_TYPE__ int
#define __WINT_WIDTH__ 32
#define __clang__ 1
#define __clang_major__ 3
#define __clang_minor__ 4
#define __clang_patchlevel__ 2
#define __clang_version__ "3.4.2 (tags/RELEASE_34/dot2-final)"
#define __cplusplus 199711L
#define __llvm__ 1
#define __pic__ 2
#define __powerpc64__ 1
#define __powerpc__ 1
#define __ppc64__ 1
#define __ppc__ 1
#define __private_extern__ extern
#define __strong
#define __unsafe_unretained
#define __weak __attribute__((objc_gc(weak)))
如果您查看 header，您会看到函数被注释 __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_2_0)。
这意味着它们从 OS_X 10.7 和 iOS 2.0 开始可用。
编译时可以查看具体的宏
我正在使用 cross-platform C++ 库。虽然该库试图成为不可知论者，但它确实有时会与 Cocoa/CocoaTouch 安全框架等框架集成。
在现代达尔文系统上，如 OS X 107、10.8 和 10.9（以及 iOS 等价物），以下工作正常。现代系统使用 Xcode 4.3 及更高版本。
#include <Secure/SecRandom.h>
在较旧的 PowerMac 运行 OS X 10.5 和 Xcode 3.1 上，包含导致 compile error。较旧的 PowerMac 仍然可以进行测试，因为它是 big-endian、PowerPC cpu.
$ make
...
/opt/local/bin/clang++-mp-3.4 -m64 -pthread -stdlib=libc++ -fPIC -fvisibility=hidden
-std=c++11 -D_REENTRANT -fstack-protector -O3 -Wall -Wextra -Ibuild/include
-c ./src/lib/entropy/darwin_secrandom/darwin_secrandom.cpp -o build/obj/lib/entropy_darwin_secrandom.o
./src/lib/entropy/darwin_secrandom/darwin_secrandom.cpp:10:10: fatal error:
'Security/SecRandom.h' file not found
#include <Security/SecRandom.h>
^
1 error generated.
make: *** [build/obj/lib/entropy_darwin_secrandom.o] Error 1
我的问题是，我们如何判断 <Security/SecRandom.h> 何时可用？它与 Xcode 4 及更高版本相关吗？或者它与其他东西有关？如果是这样，我们使用什么预处理器宏来检测可用性？
当我查看预处理器宏时，我没有看到用于向用户发出信号的内容。显然，MacPorts 编译器正在与 Cocoa 和 CocoaTouch 等框架集成（或了解），因为我们可以包含 headers，例如 TargetConditionals.h:
$ /opt/local/bin/clang++-mp-3.4 -m64 -pthread -stdlib=libc++ -fPIC -include TargetConditionals.h -x c++ -dM -E - < /dev/null | sort
#define OBJC_NEW_PROPERTIES 1
#define TARGET_CPU_68K 0
#define TARGET_CPU_ALPHA 0
#define TARGET_CPU_MIPS 0
#define TARGET_CPU_PPC 1
#define TARGET_CPU_PPC64 0
#define TARGET_CPU_SPARC 0
#define TARGET_CPU_X86 0
#define TARGET_CPU_X86_64 0
#define TARGET_OS_EMBEDDED 0
#define TARGET_OS_MAC 1
#define TARGET_OS_UNIX 0
#define TARGET_OS_WIN32 0
#define TARGET_RT_64_BIT 0
#define TARGET_RT_BIG_ENDIAN 1
#define TARGET_RT_LITTLE_ENDIAN 0
#define TARGET_RT_MAC_CFM 0
#define TARGET_RT_MAC_MACHO 1
#define _ARCH_PPC 1
#define _ARCH_PPC64 1
#define _BIG_ENDIAN 1
#define _LP64 1
#define _REENTRANT 1
#define __APPLE_CC__ 6000
#define __APPLE__ 1
#define __ATOMIC_ACQUIRE 2
#define __ATOMIC_ACQ_REL 4
#define __ATOMIC_CONSUME 1
#define __ATOMIC_RELAXED 0
#define __ATOMIC_RELEASE 3
#define __ATOMIC_SEQ_CST 5
#define __BIG_ENDIAN__ 1
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
#define __CHAR16_TYPE__ unsigned short
#define __CHAR32_TYPE__ unsigned int
#define __CHAR_BIT__ 8
#define __CONSTANT_CFSTRINGS__ 1
#define __DBL_DENORM_MIN__ 4.9406564584124654e-324
#define __DBL_DIG__ 15
#define __DBL_EPSILON__ 2.2204460492503131e-16
#define __DBL_HAS_DENORM__ 1
#define __DBL_HAS_INFINITY__ 1
#define __DBL_HAS_QUIET_NAN__ 1
#define __DBL_MANT_DIG__ 53
#define __DBL_MAX_10_EXP__ 308
#define __DBL_MAX_EXP__ 1024
#define __DBL_MAX__ 1.7976931348623157e+308
#define __DBL_MIN_10_EXP__ (-307)
#define __DBL_MIN_EXP__ (-1021)
#define __DBL_MIN__ 2.2250738585072014e-308
#define __DECIMAL_DIG__ 33
#define __DEPRECATED 1
#define __DYNAMIC__ 1
#define __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ 1050
#define __EXCEPTIONS 1
#define __FINITE_MATH_ONLY__ 0
#define __FLT_DENORM_MIN__ 1.40129846e-45F
#define __FLT_DIG__ 6
#define __FLT_EPSILON__ 1.19209290e-7F
#define __FLT_EVAL_METHOD__ 0
#define __FLT_HAS_DENORM__ 1
#define __FLT_HAS_INFINITY__ 1
#define __FLT_HAS_QUIET_NAN__ 1
#define __FLT_MANT_DIG__ 24
#define __FLT_MAX_10_EXP__ 38
#define __FLT_MAX_EXP__ 128
#define __FLT_MAX__ 3.40282347e+38F
#define __FLT_MIN_10_EXP__ (-37)
#define __FLT_MIN_EXP__ (-125)
#define __FLT_MIN__ 1.17549435e-38F
#define __FLT_RADIX__ 2
#define __GCC_ATOMIC_BOOL_LOCK_FREE 2
#define __GCC_ATOMIC_CHAR16_T_LOCK_FREE 2
#define __GCC_ATOMIC_CHAR32_T_LOCK_FREE 2
#define __GCC_ATOMIC_CHAR_LOCK_FREE 2
#define __GCC_ATOMIC_INT_LOCK_FREE 2
#define __GCC_ATOMIC_LLONG_LOCK_FREE 2
#define __GCC_ATOMIC_LONG_LOCK_FREE 2
#define __GCC_ATOMIC_POINTER_LOCK_FREE 2
#define __GCC_ATOMIC_SHORT_LOCK_FREE 2
#define __GCC_ATOMIC_TEST_AND_SET_TRUEVAL 1
#define __GCC_ATOMIC_WCHAR_T_LOCK_FREE 2
#define __GNUC_GNU_INLINE__ 1
#define __GNUC_MINOR__ 2
#define __GNUC_PATCHLEVEL__ 1
#define __GNUC__ 4
#define __GNUG__ 4
#define __GXX_ABI_VERSION 1002
#define __GXX_RTTI 1
#define __GXX_WEAK__ 1
#define __INT16_TYPE__ short
#define __INT32_TYPE__ int
#define __INT64_C_SUFFIX__ L
#define __INT64_TYPE__ long int
#define __INT8_TYPE__ char
#define __INTMAX_MAX__ 9223372036854775807L
#define __INTMAX_TYPE__ long int
#define __INTMAX_WIDTH__ 64
#define __INTPTR_TYPE__ long int
#define __INTPTR_WIDTH__ 64
#define __INT_MAX__ 2147483647
#define __LDBL_DENORM_MIN__ 4.94065645841246544176568792868221e-324L
#define __LDBL_DIG__ 31
#define __LDBL_EPSILON__ 4.94065645841246544176568792868221e-324L
#define __LDBL_HAS_DENORM__ 1
#define __LDBL_HAS_INFINITY__ 1
#define __LDBL_HAS_QUIET_NAN__ 1
#define __LDBL_MANT_DIG__ 106
#define __LDBL_MAX_10_EXP__ 308
#define __LDBL_MAX_EXP__ 1024
#define __LDBL_MAX__ 1.79769313486231580793728971405301e+308L
#define __LDBL_MIN_10_EXP__ (-291)
#define __LDBL_MIN_EXP__ (-968)
#define __LDBL_MIN__ 2.00416836000897277799610805135016e-292L
#define __LONG_DOUBLE_128__ 1
#define __LONG_LONG_MAX__ 9223372036854775807LL
#define __LONG_MAX__ 9223372036854775807L
#define __LP64__ 1
#define __MACH__ 1
#define __NATURAL_ALIGNMENT__ 1
#define __NO_INLINE__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
#define __PIC__ 2
#define __POINTER_WIDTH__ 64
#define __POWERPC__ 1
#define __PPC64__ 1
#define __PPC__ 1
#define __PRAGMA_REDEFINE_EXTNAME 1
#define __PTRDIFF_TYPE__ long int
#define __PTRDIFF_WIDTH__ 64
#define __REGISTER_PREFIX__
#define __SCHAR_MAX__ 127
#define __SHRT_MAX__ 32767
#define __SIG_ATOMIC_WIDTH__ 32
#define __SIZEOF_DOUBLE__ 8
#define __SIZEOF_FLOAT__ 4
#define __SIZEOF_INT128__ 16
#define __SIZEOF_INT__ 4
#define __SIZEOF_LONG_DOUBLE__ 16
#define __SIZEOF_LONG_LONG__ 8
#define __SIZEOF_LONG__ 8
#define __SIZEOF_POINTER__ 8
#define __SIZEOF_PTRDIFF_T__ 8
#define __SIZEOF_SHORT__ 2
#define __SIZEOF_SIZE_T__ 8
#define __SIZEOF_WCHAR_T__ 4
#define __SIZEOF_WINT_T__ 4
#define __SIZE_MAX__ 18446744073709551615UL
#define __SIZE_TYPE__ long unsigned int
#define __SIZE_WIDTH__ 64
#define __STDC_HOSTED__ 1
#define __STDC_UTF_16__ 1
#define __STDC_UTF_32__ 1
#define __STDC__ 1
#define __TARGETCONDITIONALS__
#define __UINTMAX_TYPE__ long unsigned int
#define __USER_LABEL_PREFIX__ _
#define __VERSION__ "4.2.1 Compatible Clang 3.4.2 (tags/RELEASE_34/dot2-final)"
#define __WCHAR_MAX__ 2147483647
#define __WCHAR_TYPE__ int
#define __WCHAR_WIDTH__ 32
#define __WINT_TYPE__ int
#define __WINT_WIDTH__ 32
#define __clang__ 1
#define __clang_major__ 3
#define __clang_minor__ 4
#define __clang_patchlevel__ 2
#define __clang_version__ "3.4.2 (tags/RELEASE_34/dot2-final)"
#define __cplusplus 199711L
#define __llvm__ 1
#define __pic__ 2
#define __powerpc64__ 1
#define __powerpc__ 1
#define __ppc64__ 1
#define __ppc__ 1
#define __private_extern__ extern
#define __strong
#define __unsafe_unretained
#define __weak __attribute__((objc_gc(weak)))
如果您查看 header，您会看到函数被注释 __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_2_0)。
这意味着它们从 OS_X 10.7 和 iOS 2.0 开始可用。
编译时可以查看具体的宏