無法從谷歌協議緩沖區編譯示例

Question

我搜索其他主題，但它們對我沒有幫助 =(。在我的工作服務器上，我沒有 sudo 權限，所以我安裝了 PB

./configure --prefix=/home/username/local

然后我用“person”示例創建源文件並成功地用 protoc 編譯它。

我沒有 pkg​​-info =(。我試着用

g++ -I /home/username/local/include -L /home/username/local/lib -lprotobuf -lpthread main.cpp person.pb.cc

然后有十億個模擬錯誤，即

person.pb.cc:(.text+0x4cf)：對`google::protobuf::internal::kEmptyString'的未定義引用

我認為，這是鏈接問題，但如何解決？

echo $LD_LIBRARY_PATH /home/username/local/lib

在 main.cpp 中：

#include "person.pb.h"
...

謝謝。

Answer 1

將庫放在最后：

g++ -I /home/username/local/include -L /home/username/local/lib main.cpp person.pb.cc -lprotobuf -pthread

從GCC 鏈接選項：

-llibrary
-l library
    Search the library named library when linking. 
    (The second alternative with the library as a separate argument
    is only for POSIX compliance and is not recommended.)

    It makes a difference where in the command you write this option;
    the linker searches and processes libraries and object files in the
    order they are specified.
    Thus, `foo.o -lz bar.o' searches library `z' after file foo.o but
    before bar.o. If bar.o refers to functions in `z', those functions
    may not be loaded.

此外，使用-pthread而不是-lpthread因為-pthread可能會為預處理器和鏈接器設置標志。

Answer 2

庫鏈接標志位於編譯器參數的末尾：

g++ -I /home/username/local/include -L /home/username/local/lib main.cpp person.pb.cc -lprotobuf -lpthread

Answer 3

還有一個非常普遍的問題，不僅適用於鏈接 protobuf，也適用於其他庫。 由於這是我的問題，因此我會將解決方案放在這里，也許有人會覺得它有用。

確保您嘗試鏈接到具有相同 ABI 的庫。 C++ ABI 在 GCC 4.7.0 中發生了變化。 因此，您不能將使用 GCC<4.7.0 編譯的庫（如果您像我的情況一樣從包存儲庫中獲取包，則可能是 protobuf）與使用 GCC>4.7.0 編譯的庫鏈接。

這個問題可以通過讓植物鏈接抱怨 std::basic_string 和 std::list 來識別，因為這是 C++ 中最突出的 ABI 變化。 我的鏈接器尖叫看起來像這樣：

    /bincrafters/stable/package/c0c1ef10e3d0ded44179e28b669d6aed0277ca6a/lib  -L/home/adam/.conan/data/libpcap/1.8.1/bincrafters/stable/package/0a813c597d519ec14c71192b99d7de0a92bbc1c3/lib  -L/home/adam/.conan/data/zmq/4.2.2/bincrafters/stable/package/0144a3b0aceb8edb5e63295c432a8de8020ab1b7/lib  -L/home/adam/.conan/data/libsodium/1.0.16/bincrafters/stable/package/db2ca884c9793e0b0fb54ec3f846326d1addacc8/lib -Wl,-rpath,/hoar, std::char_traits<char>, std::allocator<char> > const&, google::protobuf::io::CodedOutputStream*)'
CMakeFiles/NetworkMonitor.dir/addressbook.pb.cc.o: In function `tutorial::Person_PhoneNumber::InternalSerializeWithCachedSizesToArray(unsigned char*) const':
/home/adam/.conan/data/protobuf/3.9.1/bincrafters/stable/package/053ea29eb0edc6b1695c893b738a971110c756fd/include/google/protobuf/wire_format_lite.h:1673: undefined reference to `google::protobuf::io::CodedOutputStream::WriteStringWithSizeToArray(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned char*)'
/home/adam/.conan/data/protobuf/3.9.1/bincrafters/stable/package/053ea29eb0edc6b1695c893b738a971110c756fd/include/google/protobuf/wire_format_lite.h:1673: undefined reference to `google::protobuf::io::CodedOutputStream::WriteStringWithSizeToArray(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned char*)'
CMakeFiles/NetworkMonitor.dir/addressbook.pb.cc.o: In function `google::protobuf::internal::GetEmptyStringAlreadyInited[abi:cxx11]()':
/home/adam/.conan/data/protobuf/3.9.1/bincrafters/stable/package/053ea29eb0edc6b1695c893b738a971110c756fd/include/google/protobuf/message_lite.h:153: undefined reference to `google::protobuf::internal::fixed_address_empty_string[abi:cxx11]'
CMakeFiles/NetworkMonitor.dir/addressbook.pb.cc.o: In function `google::protobuf::internal::WireFormatLite::ReadString(google::protobuf::io::CodedInputStream*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*)':
/home/adam/.conan/data/protobuf/3.9.1/bincrafters/stable/package/053ea29eb0edc6b1695c893b738a971110c756fd/include/google/protobuf/wire_format_lite.h:880: undefined reference to `google::protobuf::internal::WireFormatLite::ReadBytes(google::protobuf::io::CodedInputStream*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*)'
CMakeFiles/NetworkMonitor.dir/addressbook.pb.cc.o:(.data.rel.ro._ZTVN8tutorial11AddressBookE[_ZTVN8tutorial11AddressBookE]+0x20): undefined reference to `google::protobuf::Message::GetTypeName[abi:cxx11]() const'
CMakeFiles/NetworkMonitor.dir/addressbook.pb.cc.o:(.data.rel.ro._ZTVN8tutorial11AddressBookE[_ZTVN8tutorial11AddressBookE]+0x58): undefined reference to `google::protobuf::Message::InitializationErrorString[abi:cxx11]() const'
CMakeFiles/NetworkMonitor.dir/addressbook.pb.cc.o:(.data.rel.ro._ZTVN8tutorial6PersonE[_ZTVN8tutorial6PersonE]+0x20): undefined reference to `google::protobuf::Message::GetTypeName[abi:cxx11]() const'
CMakeFiles/NetworkMonitor.dir/addressbook.pb.cc.o:(.data.rel.ro._ZTVN8tutorial6PersonE[_ZTVN8tutorial6PersonE]+0x58): undefined reference to `google::protobuf::Message::InitializationErrorString[abi:cxx11]() const'
CMakeFiles/NetworkMonitor.dir/addressbook.pb.cc.o:(.data.rel.ro._ZTVN8tutorial18Person_PhoneNumberE[_ZTVN8tutorial18Person_PhoneNumberE]+0x20): undefined reference to `google::protobuf::Message::GetTypeName[abi:cxx11]() const'
make[2]: *** [bin/N

在我為 conan 定義了一個配置文件並鏈接到使用相同版本的 C++ ABI 編譯的庫后，問題就消失了。