Protobuf的一个链接错误

Xcode 中编译protobuf, 编译没有问题，上层库链接protobuf库的时候报6链接错误 ：

clang: warning: libstdc++ is deprecated; move to libc++ [-Wdeprecated]
Undefined symbols for architecture x86_64:
  "cloopen_google::protobuf::io::StringOutputStream::StringOutputStream(std::string*)", referenced from:
      VideoSenderStatisticsInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      VideoReceiverStatisticsInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      AudioSenderStatisticsInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      AudioReceiverStatisticsInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      MediaStatisticsInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      MediaStatisticsDataInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      UserAuthRespInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(UserAuthResp.pb.o)
      ...
  "cloopen_google::protobuf::internal::WireFormatLite::ReadString(cloopen_google::protobuf::io::CodedInputStream*, std::string*)", referenced from:
      VideoSenderStatisticsInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      VideoReceiverStatisticsInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      AudioSenderStatisticsInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      AudioReceiverStatisticsInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      MediaStatisticsDataInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      UserAuthRespInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(UserAuthResp.pb.o)
      ServerAddr::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(UserAuthResp.pb.o)
      ...
  "cloopen_google::protobuf::internal::WireFormatLite::WriteBytesMaybeAliased(int, std::string const&, cloopen_google::protobuf::io::CodedOutputStream*)", referenced from:
      MsgLiteInner::SerializeWithCachedSizes(cloopen_google::protobuf::io::CodedOutputStream*) const in libCCPiPhoneSDK_Mac.a(MsgLite.pb.o)
  "cloopen_google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(int, std::string const&, cloopen_google::protobuf::io::CodedOutputStream*)", referenced from:
      VideoSenderStatisticsInner::SerializeWithCachedSizes(cloopen_google::protobuf::io::CodedOutputStream*) const in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      VideoReceiverStatisticsInner::SerializeWithCachedSizes(cloopen_google::protobuf::io::CodedOutputStream*) const in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      AudioSenderStatisticsInner::SerializeWithCachedSizes(cloopen_google::protobuf::io::CodedOutputStream*) const in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      AudioReceiverStatisticsInner::SerializeWithCachedSizes(cloopen_google::protobuf::io::CodedOutputStream*) const in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      MediaStatisticsDataInner::SerializeWithCachedSizes(cloopen_google::protobuf::io::CodedOutputStream*) const in libCCPiPhoneSDK_Mac.a(MediaStatisticsData.pb.o)
      UserAuthRespInner::SerializeWithCachedSizes(cloopen_google::protobuf::io::CodedOutputStream*) const in libCCPiPhoneSDK_Mac.a(UserAuthResp.pb.o)
      ServerAddr::SerializeWithCachedSizes(cloopen_google::protobuf::io::CodedOutputStream*) const in libCCPiPhoneSDK_Mac.a(UserAuthResp.pb.o)
      ...
  "cloopen_google::protobuf::internal::WireFormatLite::ReadBytes(cloopen_google::protobuf::io::CodedInputStream*, std::string*)", referenced from:
      MsgLiteInner::MergePartialFromCodedStream(cloopen_google::protobuf::io::CodedInputStream*) in libCCPiPhoneSDK_Mac.a(MsgLite.pb.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

排查：
函数所在实现文件已经编译进去，函数也没有被宏控制漏编；
奇怪，
最终排查原因：
protobuf 工程设置中 C++ Standard Library 设置的为 LLVM 的 libc++， 上层库编译使用的为GNU 实现的 libstdc++ ， 两者设置为一致，链接OK!

protobuf 工程编译设置

其实从编译器报错第一句大致也能看出端倪

clang: warning: libstdc++ is deprecated; move to libc++ 

不赞成用libstdc++，基本就是这块的问题。看来LLVM和GNU两套实现的c++标准库还是不要混用！