c++ - 另一个 undefined reference 错误

Question

我正在愉快地编码，以为一切都很好，直到..

libtool: link: g++ -g -O2 -o bbcp bbcp-main.o bbcp-server.o bbcp-client.o bbcp-client_manager.o bbcp-bbcp.pb.o -pthread  -lconfig++ /usr/lib/libprotobuf.so -lz -lpthread -lglog -L/usr/lib -lboost_thread-mt -lboost_system -pthread
bbcp-client_manager.o: In function `BBCP::Server::ClientManager::send_message(boost::shared_ptr<BBCP::Server::Client>, BBCP::Protocol::Message const&)':
/home/eax/BBCP/src/client_manager.cpp:63: undefined reference to `void BBCP::Server::Client::sendPacket<BBCP::Protocol::Message>(BBCP::Protocol::PacketType, BBCP::Protocol::Message const&)'
collect2: ld returned 1 exit status

这个不太开心的错误让我一头雾水......

client_manager.cpp:

void BBCP::Server::ClientManager::send_message(BBCP::Server::client_ptr client, BBCP::Protocol::Message const &message) {
    google::protobuf::RepeatedPtrField<BBCP::Protocol::Destination> destinations = message.destination();
    BBCP::Protocol::Destination *tmp;
    BBCP::Protocol::Message msg = message;
    std::string tmp_nickname;
    client_ptr tmp_target;
    int x;

    if (!msg.has_sender() || msg.destination_size() == 0) {
        return;
    }

    for (x = 0; x < msg.destination_size(); ++x) {
        tmp_nickname = (destinations.Get(x)).nickname();

        if ((tmp_target = get_nickname(tmp_nickname))) {
            msg.clear_destination();
            tmp = msg.add_destination();
            tmp->set_nickname(tmp_nickname);

            tmp_target->sendPacket<BBCP::Protocol::Message>(BBCP::Protocol::SINGLE_MESSAGE, msg); // this is the line of the error
        }
        else {
            client->sendError(BBCP::Protocol::DESTINATION_UNKNOWN, tmp_nickname);
        }
    }

    return;
}

client_ptr等于 boost::shared_ptr<BBCP::Server::Client> .

然后我们有client.cpp:

template<class T>
void BBCP::Server::Client::sendPacket(enum BBCP::Protocol::PacketType type, T const &packet) {
    std::vector<unsigned char> pbuffer;
    BBCP::Protocol::Header header;

    header.set_type(type);
    header.set_length(packet.ByteSize());
    pbuffer.resize(BBCP_HDR_MSG_SIZE + packet.ByteSize());

    if (!header.SerializeToArray(&pbuffer[0], BBCP_HDR_MSG_SIZE)) {
        LOG(ERROR) << "Header of type " << type << " and length " << packet.ByteSize() << " failed to serialize to array. Send aborted.";
    }
    else if (!packet.SerializeToArray(&pbuffer[BBCP_HDR_MSG_SIZE], packet.ByteSize())) {
        LOG(ERROR) << "Packet of type " << type << " and length " << packet.ByteSize() << " failed to serialize to array. Send aborted.";
    }
    else {
        boost::asio::async_write(*socket, boost::asio::buffer(&pbuffer[0], pbuffer.size()), boost::bind(&BBCP::Server::Client::sendPacketWriteHandler, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));
    }

   return;
}

此函数在BBCP::Server::Client 中的定义方式相同作为公共(public)成员。

一如既往，我们将不胜感激。

朱利安。

Answer 1

只要您在相应的源文件中显式实例化模板，就可以在 C++ 源代码中定义 [member] 函数模板。仅在源中定义成员函数模板并在不同的源中使用是行不通的。你可以尝试在成员函数模板的定义之后添加这样的东西:

template void BBCP::Server::Client::sendPacket<BBCP::Protocol::Message>(
    BBCP::Protocol::PacketType, BBCP::Protocol::Message const &packet);

当然，这假定 BBCP::Protocol::Message 已在此时定义。