Question

I’m having a problem trying to use ZeroMQ in my new application. Please note: I have no problem downloading and building ZeroMQ itself. I downloaded the ZeroMQ ZIP file, opened the project/solution file in Visual Studio/C++ 2008 and built the ZeroMQ library just fine. The /lib directory of the ZeroMQ install folder contains the .lib, .dll, and other files, so all is well there as far as I know.

My problem is that I am trying to build a simple project consisting of the HelloWorld server example in the ZeroMQ user guide. I created the following file called helloserver.c.

//
// Hello World server
// Binds REP socket to tcp://*:5555
// Expects "Hello" from client, replies with "World"
//
#include <zmq.h>
#include <stdio.h>
#include <string.h>

int main (void)
{
zmq_msg_t request;
zmq_msg_t reply;

void *context = zmq_init (1);

// Socket to talk to clients
void *responder = zmq_socket (context, ZMQ_REP);
zmq_bind (responder, "tcp://*:5555");

while (1) {
// Wait for next request from client

    zmq_msg_init (&request);
    zmq_recvmsg (responder, &request, 0);
    printf ("Received Hello\n");
    zmq_msg_close (&request);

// Do some 'work'
    Sleep (1);

// Send reply back to client
    zmq_msg_init_size (&reply, 5);
    memcpy (zmq_msg_data (&reply), "World", 5);
    zmq_sendmsg (responder, &reply, 0);
    zmq_msg_close (&reply);
}
// We never get here but if we did, this would be how we end
zmq_close (responder);
zmq_term (context);
return 0;
}

I added the ZeroMQ installatiion include directory to the VC++2008 include path (Properties->Configuration Properties->C/C++->General->Additional Include Directories) and I also added the ZeroMQ lib directory to the project:
(Properties->Configuration Properties->C/C++->Code Generation->Runtime Library, selected Multithreaded Debug DLL /MDd).

I tried to build the project. Everything compiles fine butI get a bunch of unresolved externals like this when linking:

1>Linking…
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_term referenced in function _main
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_close referenced in function _main
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_sendmsg referenced in function _main
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_msg_data referenced in function _main
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_msg_init_size referenced in function _main
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_msg_close referenced in function _main
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_recvmsg referenced in function _main
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_msg_init referenced in function _main
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_bind referenced in function _main
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_socket referenced in function _main
1>helloserver.obj : error LNK2019: unresolved external symbol _imp_zmq_init referenced in function _main
1>C:\work\visualc++2008\projects\HelloZMQServer\Debug\HelloZMQServer.exe : fatal error LNK1120: 11 unresolved externals

I tried going back to the Code generation->Runtime library settings and tried changing the library switch to ?MD or /MT but nothing worked, I still get these linker errors.

Please note that when I created helloworld.c I used an empty windows console application project, and the only changes I made were to add the ZeroMQ include and lib directories as indicated above. I have not changed any other default project settings. I’m guessing I’m missing a project setting somewhere.

How can I fix this?

Answer 1

You didn’t mention that you also added the concrete lib to your project. Note that it doesn’t suffice to tell VS only the lib path, but you must also add the lib itself to your project. I don’t have Visual Studio at hand right now, but you will find this option within the project’s linker settings. There you can mention all libs you want to link against.