我似乎无法让代码块 13.12 在 clang++ 和 g++ 中正确编译 c++11。我在使用 clang++ 编译时附加了 -std=c++11 和 -stdlib=libc++。这会导致链接错误。对于 g++，当您添加 -std=c++11 或 -std=c++0x 时，编译器无法找到随机 header 。当我使用 clang++ 和 g++ 在终端中手动编译代码时，这些错误都没有发生。
完整的链接器错误太长而无法发布，因此我将仅发布 -v 调用提供的信息。
在使用带有 -std=c++11 和 -stdlib=libc++ 的 clang++ 的代码块中:
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin12.5.0
Thread model: posix
"/usr/bin/ld" -demangle -dynamic -arch x86_64 -macosx_version_min 10.8.0 -o bin/Release/p_class_test obj/Release/Thread_Pool/thread_helper.o obj/Release/Thread_Pool/thread_pool.o obj/Release/Desktop/kmap_testing/hash_methods.o obj/Release/Desktop/p_class_test/p_classtest.o obj/Release/Desktop/p_class_test/refmanager.o -lstdc++ -lSystem /usr/bin/../lib/clang/5.1/lib/darwin/libclang_rt.osx.a
使用带有 -std=c++11 和 -stdlib=libc++ 的 clang++ 在终端中编译:
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin12.5.0
Thread model: posix
"/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.8.0 -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name thread_helper.cpp -mrelocation-model pic -pic-level 2 -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 236.3 -v -resource-dir /usr/bin/../lib/clang/5.1 -I /Users/zacharykraus/Desktop/p_class_test/ -I /Users/zacharykraus/Thread_Pool/ -I /Users/zacharykraus/Desktop/kmap_testing/ -stdlib=libc++ -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /Users/zacharykraus -ferror-limit 19 -fmessage-length 80 -stack-protector 1 -mstackrealign -fblocks -fobjc-runtime=macosx-10.8.0 -fencode-extended-block-signature -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -vectorize-slp -o /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T/thread_helper-57c077.o -x c++ /Users/zacharykraus/Thread_Pool/thread_helper.cpp
clang -cc1 version 5.1 based upon LLVM 3.4svn default target x86_64-apple-darwin12.5.0
ignoring nonexistent directory "/usr/include/c++/v1"
#include "..." search starts here:
#include <...> search starts here:
/Users/zacharykraus/Desktop/p_class_test
/Users/zacharykraus/Thread_Pool
/Users/zacharykraus/Desktop/kmap_testing
/usr/bin/../lib/c++/v1
/usr/local/include
/usr/bin/../lib/clang/5.1/include
/usr/include
/System/Library/Frameworks (framework directory)
/Library/Frameworks (framework directory)
End of search list.
"/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.8.0 -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name thread_pool.cpp -mrelocation-model pic -pic-level 2 -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 236.3 -v -resource-dir /usr/bin/../lib/clang/5.1 -I /Users/zacharykraus/Desktop/p_class_test/ -I /Users/zacharykraus/Thread_Pool/ -I /Users/zacharykraus/Desktop/kmap_testing/ -stdlib=libc++ -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /Users/zacharykraus -ferror-limit 19 -fmessage-length 80 -stack-protector 1 -mstackrealign -fblocks -fobjc-runtime=macosx-10.8.0 -fencode-extended-block-signature -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -vectorize-slp -o /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T/thread_pool-321d19.o -x c++ /Users/zacharykraus/Thread_Pool/thread_pool.cpp
clang -cc1 version 5.1 based upon LLVM 3.4svn default target x86_64-apple-darwin12.5.0
ignoring nonexistent directory "/usr/include/c++/v1"
#include "..." search starts here:
#include <...> search starts here:
/Users/zacharykraus/Desktop/p_class_test
/Users/zacharykraus/Thread_Pool
/Users/zacharykraus/Desktop/kmap_testing
/usr/bin/../lib/c++/v1
/usr/local/include
/usr/bin/../lib/clang/5.1/include
/usr/include
/System/Library/Frameworks (framework directory)
/Library/Frameworks (framework directory)
End of search list.
"/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.8.0 -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name hash_methods.cpp -mrelocation-model pic -pic-level 2 -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 236.3 -v -resource-dir /usr/bin/../lib/clang/5.1 -I /Users/zacharykraus/Desktop/p_class_test/ -I /Users/zacharykraus/Thread_Pool/ -I /Users/zacharykraus/Desktop/kmap_testing/ -stdlib=libc++ -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /Users/zacharykraus -ferror-limit 19 -fmessage-length 80 -stack-protector 1 -mstackrealign -fblocks -fobjc-runtime=macosx-10.8.0 -fencode-extended-block-signature -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -vectorize-slp -o /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T/hash_methods-b28b1b.o -x c++ /Users/zacharykraus/Desktop/kmap_testing/hash_methods.cpp
clang -cc1 version 5.1 based upon LLVM 3.4svn default target x86_64-apple-darwin12.5.0
ignoring nonexistent directory "/usr/include/c++/v1"
#include "..." search starts here:
#include <...> search starts here:
/Users/zacharykraus/Desktop/p_class_test
/Users/zacharykraus/Thread_Pool
/Users/zacharykraus/Desktop/kmap_testing
/usr/bin/../lib/c++/v1
/usr/local/include
/usr/bin/../lib/clang/5.1/include
/usr/include
/System/Library/Frameworks (framework directory)
/Library/Frameworks (framework directory)
End of search list.
"/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.8.0 -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name p_classtest.cpp -mrelocation-model pic -pic-level 2 -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 236.3 -v -resource-dir /usr/bin/../lib/clang/5.1 -I /Users/zacharykraus/Desktop/p_class_test/ -I /Users/zacharykraus/Thread_Pool/ -I /Users/zacharykraus/Desktop/kmap_testing/ -stdlib=libc++ -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /Users/zacharykraus -ferror-limit 19 -fmessage-length 80 -stack-protector 1 -mstackrealign -fblocks -fobjc-runtime=macosx-10.8.0 -fencode-extended-block-signature -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -vectorize-slp -o /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T/p_classtest-ad56a5.o -x c++ /Users/zacharykraus/Desktop/p_class_test/p_classtest.cpp
clang -cc1 version 5.1 based upon LLVM 3.4svn default target x86_64-apple-darwin12.5.0
ignoring nonexistent directory "/usr/include/c++/v1"
#include "..." search starts here:
#include <...> search starts here:
/Users/zacharykraus/Desktop/p_class_test
/Users/zacharykraus/Thread_Pool
/Users/zacharykraus/Desktop/kmap_testing
/usr/bin/../lib/c++/v1
/usr/local/include
/usr/bin/../lib/clang/5.1/include
/usr/include
/System/Library/Frameworks (framework directory)
/Library/Frameworks (framework directory)
End of search list.
"/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.8.0 -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name refmanager.cpp -mrelocation-model pic -pic-level 2 -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 236.3 -v -resource-dir /usr/bin/../lib/clang/5.1 -I /Users/zacharykraus/Desktop/p_class_test/ -I /Users/zacharykraus/Thread_Pool/ -I /Users/zacharykraus/Desktop/kmap_testing/ -stdlib=libc++ -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /Users/zacharykraus -ferror-limit 19 -fmessage-length 80 -stack-protector 1 -mstackrealign -fblocks -fobjc-runtime=macosx-10.8.0 -fencode-extended-block-signature -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -vectorize-slp -o /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T/refmanager-d17474.o -x c++ /Users/zacharykraus/Desktop/p_class_test/refmanager.cpp
clang -cc1 version 5.1 based upon LLVM 3.4svn default target x86_64-apple-darwin12.5.0
ignoring nonexistent directory "/usr/include/c++/v1"
#include "..." search starts here:
#include <...> search starts here:
/Users/zacharykraus/Desktop/p_class_test
/Users/zacharykraus/Thread_Pool
/Users/zacharykraus/Desktop/kmap_testing
/usr/bin/../lib/c++/v1
/usr/local/include
/usr/bin/../lib/clang/5.1/include
/usr/include
/System/Library/Frameworks (framework directory)
/Library/Frameworks (framework directory)
End of search list.
"/usr/bin/ld" -demangle -dynamic -arch x86_64 -macosx_version_min 10.8.0 -o nork /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T/thread_helper-57c077.o /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T/thread_pool-321d19.o /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T/hash_methods-b28b1b.o /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T/p_classtest-ad56a5.o /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T/refmanager-d17474.o -lc++ -lSystem /usr/bin/../lib/clang/5.1/lib/darwin/libclang_rt.osx.a
不幸的是，我无法在终端中比较代码块 g++ 和 g++。
但是基于 clang 中两个不同编译的输出。在链接步骤中，代码块似乎没有使用 libc++ 库。您如何获得代码块以使用正确的库来链接 clang++？
我假设基于代码块中的clang问题g++正在使用较旧的c++ 03库，即使在告诉编译器切换到c++ 11时也是如此。但不幸的是，我不知道如何确认这一点。
最佳答案
我找到了clang++的答案。
显然，您必须添加 -stdlib=libc++ 作为编译器标志和链接标志。
联动输出变为
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin12.5.0
Thread model: posix
"/usr/bin/ld" -demangle -dynamic -arch x86_64 -macosx_version_min 10.8.0 -o bin/Release/p_class_test obj/Release/Thread_Pool/thread_helper.o obj/Release/Thread_Pool/thread_pool.o obj/Release/Desktop/kmap_testing/hash_methods.o obj/Release/Desktop/p_class_test/p_classtest.o obj/Release/Desktop/p_class_test/refmanager.o -lc++ -lSystem /usr/bin/../lib/clang/5.1/lib/darwin/libclang_rt.osx.a
这清楚地显示了正在使用的正确库。
之所以会出现 g++ 问题，是因为即使代码块输出它是使用 g++ 编译的，实际上它使用 clang++ 库作为编译和链接过程的一部分。虽然基于输出，如果 g++ 编译器及其包含被调用，它并不是 100% 清楚的。要解决此问题，您需要为编译和链接添加 -stdlib=libc++ 标志。为了证明苹果上的代码块实际上在后台使用了 clang 库，我附上了 -v 在链接和编译期间的输出以及代码块使用的命令。
以下是链接信息:
g++ -o bin/Debug/p_class_test obj/Debug/Thread_Pool/thread_helper.o obj/Debug/Thread_Pool/thread_pool.o obj/Debug/Desktop/kmap_testing/hash_methods.o obj/Debug/Desktop/p_class_test/p_classtest.o obj/Debug/Desktop/p_class_test/refmanager.o -v -stdlib=libc++
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin12.5.0
Thread model: posix
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -dynamic -arch x86_64 -macosx_version_min 10.8.0 -o bin/Debug/p_class_test obj/Debug/Thread_Pool/thread_helper.o obj/Debug/Thread_Pool/thread_pool.o obj/Debug/Desktop/kmap_testing/hash_methods.o obj/Debug/Desktop/p_class_test/p_classtest.o obj/Debug/Desktop/p_class_test/refmanager.o -lc++ -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/5.1/lib/darwin/libclang_rt.osx.a
这是编译的信息:
g++ -g -std=c++11 -stdlib=libc++ -v -I/Users/zacharykraus/Desktop/p_class_test/ -I/Users/zacharykraus/Thread_Pool -I/Users/zacharykraus/Desktop/kmap_testing -c /Users/zacharykraus/Desktop/p_class_test/refmanager.cpp -o obj/Debug/Desktop/p_class_test/refmanager.o
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin12.5.0
Thread model: posix
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.8.0 -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name refmanager.cpp -mrelocation-model pic -pic-level 2 -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 236.3 -v -gdwarf-2 -coverage-file /Users/zacharykraus/Desktop/p_class_test/obj/Debug/Desktop/p_class_test/refmanager.o -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/5.1 -I /Users/zacharykraus/Desktop/p_class_test/ -I /Users/zacharykraus/Thread_Pool -I /Users/zacharykraus/Desktop/kmap_testing -stdlib=libc++ -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /Users/zacharykraus/Desktop/p_class_test -ferror-limit 19 -fmessage-length 0 -stack-protector 1 -mstackrealign -fblocks -fobjc-runtime=macosx-10.8.0 -fencode-extended-block-signature -fcxx-exceptions -fexceptions -fdiagnostics-show-option -vectorize-slp -o obj/Debug/Desktop/p_class_test/refmanager.o -x c++ /Users/zacharykraus/Desktop/p_class_test/refmanager.cpp
clang -cc1 version 5.1 based upon LLVM 3.4svn default target x86_64-apple-darwin12.5.0
ignoring nonexistent directory "/usr/include/c++/v1"
#include "..." search starts here:
#include <...> search starts here:
/Users/zacharykraus/Desktop/p_class_test
/Users/zacharykraus/Thread_Pool
/Users/zacharykraus/Desktop/kmap_testing
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1
/usr/local/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/5.1/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
/usr/include
/System/Library/Frameworks (framework directory)
/Library/Frameworks (framework directory)
End of search list.
经过一番苦恼后，我终于弄清楚了 g++ 的问题出在代码块上。问题是调用 g++ 时的代码块不使用您的可执行路径。相反，它使用编译器设置中的工具链可执行路径。我的工具链可执行路径设置为苹果版 g++ 所在的/usr/bin。这个版本实际上是通过一系列复杂的调用调用clang++。我需要做的就是解决这个问题，将工具链可执行路径更改为我的实际 gnu 编译器所在的/usr/local/bin。在此更改之后，我能够摆脱 -stdlib=libc++ 并且我的编译和链接读数如下。
汇编:
g++ -g -std=c++11 -v -I/Users/zacharykraus/Desktop/p_class_test/ -I/Users/zacharykraus/Thread_Pool -I/Users/zacharykraus/Desktop/kmap_testing -c /Users/zacharykraus/Thread_Pool/thread_helper.cpp -o obj/Debug/Thread_Pool/thread_helper.o
Using built-in specs.
COLLECT_GCC=g++
Target: x86_64-apple-darwin12.5.0
Configured with: ../gcc-4.8.1/configure --enable-languages=c++,fortran
Thread model: posix
gcc version 4.8.1 (GCC)
COLLECT_GCC_OPTIONS='-mmacosx-version-min=10.8.5' '-g' '-std=c++11' '-v' '-I' '/Users/zacharykraus/Desktop/p_class_test/' '-I' '/Users/zacharykraus/Thread_Pool' '-I' '/Users/zacharykraus/Desktop/kmap_testing' '-c' '-o' 'obj/Debug/Thread_Pool/thread_helper.o' '-shared-libgcc' '-mtune=core2'
/usr/local/libexec/gcc/x86_64-apple-darwin12.5.0/4.8.1/cc1plus -quiet -v -I /Users/zacharykraus/Desktop/p_class_test/ -I /Users/zacharykraus/Thread_Pool -I /Users/zacharykraus/Desktop/kmap_testing -D__DYNAMIC__ /Users/zacharykraus/Thread_Pool/thread_helper.cpp -fPIC -feliminate-unused-debug-symbols -quiet -dumpbase thread_helper.cpp -mmacosx-version-min=10.8.5 -mtune=core2 -auxbase-strip obj/Debug/Thread_Pool/thread_helper.o -g -std=c++11 -version -o /var/folders/k5/ywc_m0js3z3byh3yqwbfmfj00000gn/T//ccVidneY.s
GNU C++ (GCC) version 4.8.1 (x86_64-apple-darwin12.5.0)
compiled by GNU C version 4.8.1, GMP version 4.3.1, MPFR version 2.4.1, MPC version 0.8.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/../../../../x86_64-apple-darwin12.5.0/include"
#include "..." search starts here:
#include <...> search starts here:
/Users/zacharykraus/Desktop/p_class_test/
/Users/zacharykraus/Thread_Pool
/Users/zacharykraus/Desktop/kmap_testing
/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/../../../../include/c++/4.8.1
/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/../../../../include/c++/4.8.1/x86_64-apple-darwin12.5.0
/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/../../../../include/c++/4.8.1/backward
/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/include
/usr/local/include
/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/include-fixed
/usr/include
/System/Library/Frameworks
/Library/Frameworks
End of search list.
链接:
g++ -o bin/Debug/p_class_test obj/Debug/Thread_Pool/thread_helper.o obj/Debug/Thread_Pool/thread_pool.o obj/Debug/Desktop/kmap_testing/hash_methods.o obj/Debug/Desktop/p_class_test/p_classtest.o obj/Debug/Desktop/p_class_test/refmanager.o -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-apple-darwin12.5.0/4.8.1/lto-wrapper
Target: x86_64-apple-darwin12.5.0
Configured with: ../gcc-4.8.1/configure --enable-languages=c++,fortran
Thread model: posix
gcc version 4.8.1 (GCC)
COMPILER_PATH=/usr/local/libexec/gcc/x86_64-apple-darwin12.5.0/4.8.1/:/usr/local/libexec/gcc/x86_64-apple-darwin12.5.0/4.8.1/:/usr/local/libexec/gcc/x86_64-apple-darwin12.5.0/:/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/:/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/
LIBRARY_PATH=/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/:/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/../../../:/usr/lib/
COLLECT_GCC_OPTIONS='-mmacosx-version-min=10.8.5' '-o' 'bin/Debug/p_class_test' '-v' '-shared-libgcc' '-mtune=core2'
/usr/local/libexec/gcc/x86_64-apple-darwin12.5.0/4.8.1/collect2 -dynamic -arch x86_64 -macosx_version_min 10.8.5 -weak_reference_mismatches non-weak -o bin/Debug/p_class_test -L/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1 -L/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/../../.. obj/Debug/Thread_Pool/thread_helper.o obj/Debug/Thread_Pool/thread_pool.o obj/Debug/Desktop/kmap_testing/hash_methods.o obj/Debug/Desktop/p_class_test/p_classtest.o obj/Debug/Desktop/p_class_test/refmanager.o -lstdc++ -no_compact_unwind -lSystem -lgcc_ext.10.5 -lgcc -lSystem -v
collect2 version 4.8.1
/usr/bin/ld -dynamic -arch x86_64 -macosx_version_min 10.8.5 -weak_reference_mismatches non-weak -o bin/Debug/p_class_test -L/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1 -L/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1/../../.. obj/Debug/Thread_Pool/thread_helper.o obj/Debug/Thread_Pool/thread_pool.o obj/Debug/Desktop/kmap_testing/hash_methods.o obj/Debug/Desktop/p_class_test/p_classtest.o obj/Debug/Desktop/p_class_test/refmanager.o -lstdc++ -no_compact_unwind -lSystem -lgcc_ext.10.5 -lgcc -lSystem -v
@(#)PROGRAM:ld PROJECT:ld64-236.4
configured to support archs: armv6 armv7 armv7s arm64 i386 x86_64 armv6m armv7m armv7em
Library search paths:
/usr/local/lib/gcc/x86_64-apple-darwin12.5.0/4.8.1
/usr/local/lib
/usr/lib
/usr/local/lib
Framework search paths:
/Library/Frameworks/
/System/Library/Frameworks/
关于代码块中的 C++11 编译问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25961623/