在 protobuf 类中没有访问或设置值的有效方法

Question

我最近一直在为 Google protobufs 苦苦挣扎。我写了一个名为Button.proto的原型文件。

这是它的内容：

syntax = "proto3";

package robotjoystick;

message Button {
  string name = 1;
  int32 id = 2;
  uint32 state = 3;
}

我用这个命令成功编译了它（将 $USER 替换为实际的计算机用户）：

protoc -I=/home/$USER/robotjoystickserver --cpp_out=/home/$USER/robotjoystickserver/proto_classes Button.proto

我正在使用 protobuf 版本 3.7.1。 我的 *.cpp 文件名为dumbprrotos.cpp，由于某种原因它没有编译。 这是我的 *.cpp 文件：

// Client side C/C++ program to demonstrate Socket programming 
#include <stdio.h> 
#include <sys/socket.h> 
#include <stdlib.h> 
#include <netinet/in.h> 
#include <string.h> 
// This line was forgotten apparently - https://stackoverflow.com/questions/15660203/inet-pton-identifier-not-found
#include <arpa/inet.h>
// This one was also forgotten - https://www.reddit.com/r/learnprogramming/comments/3tlii5/clinux_why_is_write_or_close_not_declared_in_this/   
#include <unistd.h>
// This is SDL 2.0, the joystick control library
#include <SDL2/SDL.h>
// For Ctrl+C quitting
#include <signal.h>
// for std::end 
//#include <iostream>

// Now we import the header files the protobuf compiler generated.
#include "proto_classes/Button.pb.h"

// This is a standard port
#define PORT 8080

//#include<iostream>
using namespace std;

// For the protobuf generated class.
using namespace robotjoystick;

int main(int argc, char const *argv[]) 
{
    // https://developers.google.com/protocol-buffers/docs/cpptutorial
    // Verify that the version of the library that we linked against is
    // compatible with the version of the headers we compiled against.
    GOOGLE_PROTOBUF_VERIFY_VERSION;

    // Broken method 1
    /*
    const string thename = "blah";
    robotjoystick::Button * thebutton;
    thebutton = new Button();
    thebutton->set_name("john");
    thebutton->set_id(12); 
    */

    // Broken method 2

    const string thename = "blah";
    robotjoystick::Button thebutton;
    thebutton.set_name("john");
    thebutton.set_id(12); 

    return 0; 
} 

我标记的 2 段代码是我试图完成的同一件事的 2 个版本，但两者都抛出相同类型的错误，我不知道如何解释它。我需要做什么才能编译这段代码？

我还应该提到，我在我的主目录中安装了 protobuf 3.7.1（这意味着 protobuf 的 zip 文件被解压到那里，然后安装在那里）。

我当前运行代码时得到的错误，确切的方式，我得到这个错误：

Compiling dumbprotos.cpp

/tmp/cc7HHVQf.o: In function `google::protobuf::internal::GetEmptyStringAlreadyInited[abi:cxx11]()':
dumbprotos.cpp:(.text._ZN6google8protobuf8internal27GetEmptyStringAlreadyInitedB5cxx11Ev[_ZN6google8protobuf8internal27GetEmptyStringAlreadyInitedB5cxx11Ev]+0x5): undefined reference to `google::protobuf::internal::fixed_address_empty_string[abi:cxx11]'
/tmp/ccMdby3z.o: In function `AddDescriptors_Button_2eproto()':
Button.pb.cc:(.text+0xa6): undefined reference to `google::protobuf::internal::AddDescriptors(google::protobuf::internal::DescriptorTable*, void (* const*)(), int)'
/tmp/ccMdby3z.o: In function `robotjoystick::Button::MergePartialFromCodedStream(google::protobuf::io::CodedInputStream*)':
Button.pb.cc:(.text+0x660): undefined reference to `google::protobuf::io::CodedInputStream::ReadTagFallback(unsigned int)'
Button.pb.cc:(.text+0x73f): undefined reference to `google::protobuf::internal::WireFormatLite::VerifyUtf8String(char const*, int, google::protobuf::internal::WireFormatLite::Operation, char const*)'
/tmp/ccMdby3z.o: In function `robotjoystick::Button::SerializeWithCachedSizes(google::protobuf::io::CodedOutputStream*) const':
Button.pb.cc:(.text+0x904): undefined reference to `google::protobuf::internal::WireFormatLite::VerifyUtf8String(char const*, int, google::protobuf::internal::WireFormatLite::Operation, char const*)'
/tmp/ccMdby3z.o: In function `robotjoystick::Button::InternalSerializeWithCachedSizesToArray(unsigned char*) const':
Button.pb.cc:(.text+0xa98): undefined reference to `google::protobuf::internal::WireFormatLite::VerifyUtf8String(char const*, int, google::protobuf::internal::WireFormatLite::Operation, char const*)'
/tmp/ccMdby3z.o: In function `robotjoystick::Button::GetMetadata() const':
Button.pb.cc:(.text+0x1386): undefined reference to `google::protobuf::internal::AssignDescriptors(google::protobuf::internal::AssignDescriptorsTable*)'
/tmp/ccMdby3z.o: In function `robotjoystick::Button* google::protobuf::Arena::CreateMaybeMessage<robotjoystick::Button>(google::protobuf::Arena*)':
Button.pb.cc:(.text+0x142e): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAligned(unsigned long)'
Button.pb.cc:(.text+0x144b): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAlignedAndAddCleanup(unsigned long, void (*)(void*))'
/tmp/ccMdby3z.o: In function `google::protobuf::io::CodedInputStream::ReadVarint32(unsigned int*)':
Button.pb.cc:(.text._ZN6google8protobuf2io16CodedInputStream12ReadVarint32EPj[_ZN6google8protobuf2io16CodedInputStream12ReadVarint32EPj]+0x78): undefined reference to `google::protobuf::io::CodedInputStream::ReadVarint32Fallback(unsigned int)'
/tmp/ccMdby3z.o: In function `google::protobuf::Arena::AllocHook(std::type_info const*, unsigned long) const':
Button.pb.cc:(.text._ZNK6google8protobuf5Arena9AllocHookEPKSt9type_infom[_ZNK6google8protobuf5Arena9AllocHookEPKSt9type_infom]+0x3d): undefined reference to `google::protobuf::Arena::OnArenaAllocation(std::type_info const*, unsigned long) const'
/tmp/ccMdby3z.o: In function `google::protobuf::internal::ArenaStringPtr::CreateInstance(google::protobuf::Arena*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const*)':
Button.pb.cc:(.text._ZN6google8protobuf8internal14ArenaStringPtr14CreateInstanceEPNS0_5ArenaEPKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN6google8protobuf8internal14ArenaStringPtr14CreateInstanceEPNS0_5ArenaEPKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x23e): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAligned(unsigned long)'
Button.pb.cc:(.text._ZN6google8protobuf8internal14ArenaStringPtr14CreateInstanceEPNS0_5ArenaEPKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN6google8protobuf8internal14ArenaStringPtr14CreateInstanceEPNS0_5ArenaEPKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x25b): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAlignedAndAddCleanup(unsigned long, void (*)(void*))'
/tmp/ccMdby3z.o: In function `google::protobuf::internal::InitSCC(google::protobuf::internal::SCCInfoBase*)':
Button.pb.cc:(.text._ZN6google8protobuf8internal7InitSCCEPNS1_11SCCInfoBaseE[_ZN6google8protobuf8internal7InitSCCEPNS1_11SCCInfoBaseE]+0x4d): undefined reference to `google::protobuf::internal::InitSCCImpl(google::protobuf::internal::SCCInfoBase*)'
/tmp/ccMdby3z.o: In function `google::protobuf::internal::OnShutdownDestroyMessage(void const*)':
Button.pb.cc:(.text._ZN6google8protobuf8internal24OnShutdownDestroyMessageEPKv[_ZN6google8protobuf8internal24OnShutdownDestroyMessageEPKv]+0x14): undefined reference to `google::protobuf::internal::DestroyMessage(void const*)'
Button.pb.cc:(.text._ZN6google8protobuf8internal24OnShutdownDestroyMessageEPKv[_ZN6google8protobuf8internal24OnShutdownDestroyMessageEPKv]+0x19): undefined reference to `google::protobuf::internal::OnShutdownRun(void (*)(void const*), void const*)'
/tmp/ccMdby3z.o: In function `google::protobuf::internal::InternalMetadataWithArena::default_instance()':
Button.pb.cc:(.text._ZN6google8protobuf8internal25InternalMetadataWithArena16default_instanceEv[_ZN6google8protobuf8internal25InternalMetadataWithArena16default_instanceEv]+0x5): undefined reference to `google::protobuf::UnknownFieldSet::default_instance()'
/tmp/ccMdby3z.o: In function `google::protobuf::internal::InternalMetadataWithArenaBase<google::protobuf::UnknownFieldSet, google::protobuf::internal::InternalMetadataWithArena>::mutable_unknown_fields_slow()':
Button.pb.cc:(.text._ZN6google8protobuf8internal29InternalMetadataWithArenaBaseINS0_15UnknownFieldSetENS1_25InternalMetadataWithArenaEE27mutable_unknown_fields_slowEv[_ZN6google8protobuf8internal29InternalMetadataWithArenaBaseINS0_15UnknownFieldSetENS1_25InternalMetadataWithArenaEE27mutable_unknown_fields_slowEv]+0x15c): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAligned(unsigned long)'
Button.pb.cc:(.text._ZN6google8protobuf8internal29InternalMetadataWithArenaBaseINS0_15UnknownFieldSetENS1_25InternalMetadataWithArenaEE27mutable_unknown_fields_slowEv[_ZN6google8protobuf8internal29InternalMetadataWithArenaBaseINS0_15UnknownFieldSetENS1_25InternalMetadataWithArenaEE27mutable_unknown_fields_slowEv]+0x176): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAlignedAndAddCleanup(unsigned long, void (*)(void*))'
/tmp/ccMdby3z.o:(.rodata._ZTVN13robotjoystick6ButtonE[_ZTVN13robotjoystick6ButtonE]+0xb8): undefined reference to `google::protobuf::Message::SpaceUsedLong() const'
collect2: error: ld returned 1 exit status

当我用其他损坏的场景编译代码时，

const string thename = "blah";
robotjoystick::Button * thebutton;
thebutton = new Button();
thebutton->set_name("john");
thebutton->set_id(12); 

我得到了这个错误：

Compiling dumbprotos.cpp

/tmp/ccaCT7Iy.o: In function `google::protobuf::internal::GetEmptyStringAlreadyInited[abi:cxx11]()':
dumbprotos.cpp:(.text._ZN6google8protobuf8internal27GetEmptyStringAlreadyInitedB5cxx11Ev[_ZN6google8protobuf8internal27GetEmptyStringAlreadyInitedB5cxx11Ev]+0x5): undefined reference to `google::protobuf::internal::fixed_address_empty_string[abi:cxx11]'
/tmp/ccfmvBXP.o: In function `AddDescriptors_Button_2eproto()':
Button.pb.cc:(.text+0xa6): undefined reference to `google::protobuf::internal::AddDescriptors(google::protobuf::internal::DescriptorTable*, void (* const*)(), int)'
/tmp/ccfmvBXP.o: In function `robotjoystick::Button::MergePartialFromCodedStream(google::protobuf::io::CodedInputStream*)':
Button.pb.cc:(.text+0x660): undefined reference to `google::protobuf::io::CodedInputStream::ReadTagFallback(unsigned int)'
Button.pb.cc:(.text+0x73f): undefined reference to `google::protobuf::internal::WireFormatLite::VerifyUtf8String(char const*, int, google::protobuf::internal::WireFormatLite::Operation, char const*)'
/tmp/ccfmvBXP.o: In function `robotjoystick::Button::SerializeWithCachedSizes(google::protobuf::io::CodedOutputStream*) const':
Button.pb.cc:(.text+0x904): undefined reference to `google::protobuf::internal::WireFormatLite::VerifyUtf8String(char const*, int, google::protobuf::internal::WireFormatLite::Operation, char const*)'
/tmp/ccfmvBXP.o: In function `robotjoystick::Button::InternalSerializeWithCachedSizesToArray(unsigned char*) const':
Button.pb.cc:(.text+0xa98): undefined reference to `google::protobuf::internal::WireFormatLite::VerifyUtf8String(char const*, int, google::protobuf::internal::WireFormatLite::Operation, char const*)'
/tmp/ccfmvBXP.o: In function `robotjoystick::Button::GetMetadata() const':
Button.pb.cc:(.text+0x1386): undefined reference to `google::protobuf::internal::AssignDescriptors(google::protobuf::internal::AssignDescriptorsTable*)'
/tmp/ccfmvBXP.o: In function `robotjoystick::Button* google::protobuf::Arena::CreateMaybeMessage<robotjoystick::Button>(google::protobuf::Arena*)':
Button.pb.cc:(.text+0x142e): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAligned(unsigned long)'
Button.pb.cc:(.text+0x144b): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAlignedAndAddCleanup(unsigned long, void (*)(void*))'
/tmp/ccfmvBXP.o: In function `google::protobuf::io::CodedInputStream::ReadVarint32(unsigned int*)':
Button.pb.cc:(.text._ZN6google8protobuf2io16CodedInputStream12ReadVarint32EPj[_ZN6google8protobuf2io16CodedInputStream12ReadVarint32EPj]+0x78): undefined reference to `google::protobuf::io::CodedInputStream::ReadVarint32Fallback(unsigned int)'
/tmp/ccfmvBXP.o: In function `google::protobuf::Arena::AllocHook(std::type_info const*, unsigned long) const':
Button.pb.cc:(.text._ZNK6google8protobuf5Arena9AllocHookEPKSt9type_infom[_ZNK6google8protobuf5Arena9AllocHookEPKSt9type_infom]+0x3d): undefined reference to `google::protobuf::Arena::OnArenaAllocation(std::type_info const*, unsigned long) const'
/tmp/ccfmvBXP.o: In function `google::protobuf::internal::ArenaStringPtr::CreateInstance(google::protobuf::Arena*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const*)':
Button.pb.cc:(.text._ZN6google8protobuf8internal14ArenaStringPtr14CreateInstanceEPNS0_5ArenaEPKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN6google8protobuf8internal14ArenaStringPtr14CreateInstanceEPNS0_5ArenaEPKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x23e): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAligned(unsigned long)'
Button.pb.cc:(.text._ZN6google8protobuf8internal14ArenaStringPtr14CreateInstanceEPNS0_5ArenaEPKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN6google8protobuf8internal14ArenaStringPtr14CreateInstanceEPNS0_5ArenaEPKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x25b): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAlignedAndAddCleanup(unsigned long, void (*)(void*))'
/tmp/ccfmvBXP.o: In function `google::protobuf::internal::InitSCC(google::protobuf::internal::SCCInfoBase*)':
Button.pb.cc:(.text._ZN6google8protobuf8internal7InitSCCEPNS1_11SCCInfoBaseE[_ZN6google8protobuf8internal7InitSCCEPNS1_11SCCInfoBaseE]+0x4d): undefined reference to `google::protobuf::internal::InitSCCImpl(google::protobuf::internal::SCCInfoBase*)'
/tmp/ccfmvBXP.o: In function `google::protobuf::internal::OnShutdownDestroyMessage(void const*)':
Button.pb.cc:(.text._ZN6google8protobuf8internal24OnShutdownDestroyMessageEPKv[_ZN6google8protobuf8internal24OnShutdownDestroyMessageEPKv]+0x14): undefined reference to `google::protobuf::internal::DestroyMessage(void const*)'
Button.pb.cc:(.text._ZN6google8protobuf8internal24OnShutdownDestroyMessageEPKv[_ZN6google8protobuf8internal24OnShutdownDestroyMessageEPKv]+0x19): undefined reference to `google::protobuf::internal::OnShutdownRun(void (*)(void const*), void const*)'
/tmp/ccfmvBXP.o: In function `google::protobuf::internal::InternalMetadataWithArena::default_instance()':
Button.pb.cc:(.text._ZN6google8protobuf8internal25InternalMetadataWithArena16default_instanceEv[_ZN6google8protobuf8internal25InternalMetadataWithArena16default_instanceEv]+0x5): undefined reference to `google::protobuf::UnknownFieldSet::default_instance()'
/tmp/ccfmvBXP.o: In function `google::protobuf::internal::InternalMetadataWithArenaBase<google::protobuf::UnknownFieldSet, google::protobuf::internal::InternalMetadataWithArena>::mutable_unknown_fields_slow()':
Button.pb.cc:(.text._ZN6google8protobuf8internal29InternalMetadataWithArenaBaseINS0_15UnknownFieldSetENS1_25InternalMetadataWithArenaEE27mutable_unknown_fields_slowEv[_ZN6google8protobuf8internal29InternalMetadataWithArenaBaseINS0_15UnknownFieldSetENS1_25InternalMetadataWithArenaEE27mutable_unknown_fields_slowEv]+0x15c): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAligned(unsigned long)'
Button.pb.cc:(.text._ZN6google8protobuf8internal29InternalMetadataWithArenaBaseINS0_15UnknownFieldSetENS1_25InternalMetadataWithArenaEE27mutable_unknown_fields_slowEv[_ZN6google8protobuf8internal29InternalMetadataWithArenaBaseINS0_15UnknownFieldSetENS1_25InternalMetadataWithArenaEE27mutable_unknown_fields_slowEv]+0x176): undefined reference to `google::protobuf::internal::ArenaImpl::AllocateAlignedAndAddCleanup(unsigned long, void (*)(void*))'
/tmp/ccfmvBXP.o:(.rodata._ZTVN13robotjoystick6ButtonE[_ZTVN13robotjoystick6ButtonE]+0xb8): undefined reference to `google::protobuf::Message::SpaceUsedLong() const'
collect2: error: ld returned 1 exit status

这是我用来编译代码的脚本：

#!/bin/sh
echo "Compiling dumbprotos.cpp"
echo ""
g++ dumbprotos.cpp proto_classes/Button.pb.cc -o ./pleasework -std=c++11 -lSDL2 -lprotobuf

我认为这就是我需要向你们展示的一切。我错过了什么吗？我需要做什么才能编译我的 *.cpp 代码？

我在 Ubuntu 16.04 上。

Answer 1

在考虑了@goduk 提供的评论后，我认为我应该进一步研究链接库问题并找到我需要获取的文件。事实证明，我没有链接到任何特定位置。 我决定查看protobuf-3.7.1/src/README.md 下的文档以进一步探索以找到.../lib/ 目录。重新阅读这些文档后，一个特定的部分引起了我的注意。

To compile a package that uses Protocol Buffers, you need to pass
various flags to your compiler and linker.  As of version 2.2.0,
Protocol Buffers integrates with pkg-config to manage this.  If you
have pkg-config installed, then you can invoke it to get a list of
flags like so:

    pkg-config --cflags protobuf         # print compiler flags
    pkg-config --libs protobuf           # print linker flags
    pkg-config --cflags --libs protobuf  # print both

For example:

    c++ my_program.cc my_proto.pb.cc `pkg-config --cflags --libs protobuf`

在我的笔记本电脑上，命令pkg-config --cflags --libs protobuf 返回-pthread -I/usr/local/include -L/usr/local/lib -lprotobuf -pthread。 我不需要尝试确定正确的编译标志，而是只需要在最后使用pkg-config --cflags --libs protobuf 调用所需的标志。 我以前从未听说过 pkg-config，但这解决了我所有的问题。 最终的 bash 脚本行现在是这样的：

g++ dumbprotos.cpp proto_classes/Button.pb.cc -o ./pleasework -std=c++11 -lSDL2 `pkg-config --cflags --libs protobuf`

感谢您的帮助。 （这是链接器类型问题。）

我还要提一下，如果 protobuf 对象包含其他 protobuf 对象，则必须在命令行调用中包含这些对象：

g++ my_program.cc my_proto_imported.pb.cc my_proto_containing.pb.cc `pkg-config --cflags --libs protobuf`

意思是my_proto_imported.pb.cc是在my_proto_contained.pb.cc中导入和使用的protobuf。