Yet another undefined reference error

Question

I was happily coding, thinking that everything was alright, until..

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

This not so happy error made me clueless...

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 equals to boost::shared_ptr<BBCP::Server::Client>.

Then we have 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;
}

This function is defined the same way in BBCP::Server::Client as a public member.

As always, any help will be appreciated.

Julian.

@Pubby what do you mean? the template is declared in the client header file. — Misguided
– Misguided, Commented Jan 28, 2012 at 2:02
@JulianBayardoSpadafora: Use namespaces or redesign in more readable manner. — Andrejs Cainikovs
– Andrejs Cainikovs, Commented Jan 28, 2012 at 2:04

Dietmar Kühl · Accepted Answer · 2012-01-28 02:05:07Z

2

Definition of [member] function templates in C++ sources is OK as long as you explicitly instantiate the template in the corresponding source file. Just having the member function template defined in a source and used in a different source won't work. You can try adding something like this after the the definition of the member function template:

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

Of course, this assume that BBCP::Protocol::Message is defined at this point.

answered Jan 28, 2012 at 2:05

Dietmar Kühl

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