I'm just starting to learn how to work with zeromq libraries and using them in different C++ projects. The sample code that I wrote (actually copied from there tutorials)is this:
// file: main.cpp
// Hello World client in C++
// Connects REQ socket to tcp://localhost:5555
// Sends "Hello" to server, expects "World" back
//
#include <zmq.hpp>
#include <string>
#include <iostream>
int main ()
{
// Prepare our context and socket
zmq::context_t context (1);
zmq::socket_t socket (context, ZMQ_REQ);
std::cout << "Connecting to hello world server…" << std::endl;
socket.connect ("tcp://localhost:5555");
// Do 10 requests, waiting each time for a response
for (int request_nbr = 0; request_nbr != 10; request_nbr++) {
zmq::message_t request (5);
memcpy (request.data (), "Hello", 5);
std::cout << "Sending Hello " << request_nbr << "…" << std::endl;
socket.send (request);
// Get the reply.
zmq::message_t reply;
socket.recv (&reply);
std::cout << "Received World " << request_nbr << std::endl;
}
return 0;
}
and by building the output of this file with the command below:
g++ main.cpp -o test -lzmq
the file will be generated with no problem.
The problem that I have is that I want to build the file using CMake.Thus, I've written a CMakeLists.txt
file as below:
cmake_minimum_required(VERSION 3.6)
project(test2)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -lzmq")
set(SOURCE_FILES main.cpp)
add_executable(test2 ${SOURCE_FILES})
The part that I thought will be enough to build the program is -lzmq
but even with that piece included, I get the following error messages:
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::error_t::error_t()':
/usr/include/zmq.hpp:62: undefined reference to `zmq_errno'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::error_t::what() const':
/usr/include/zmq.hpp:66: undefined reference to `zmq_strerror'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::message_t::message_t()':
/usr/include/zmq.hpp:107: undefined reference to `zmq_msg_init'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::message_t::message_t(unsigned long)':
/usr/include/zmq.hpp:114: undefined reference to `zmq_msg_init_size'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::message_t::~message_t()':
/usr/include/zmq.hpp:129: undefined reference to `zmq_msg_close'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::message_t::data()':
/usr/include/zmq.hpp:180: undefined reference to `zmq_msg_data'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::context_t::context_t(int)':
/usr/include/zmq.hpp:204: undefined reference to `zmq_init'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::context_t::~context_t()':
/usr/include/zmq.hpp:225: undefined reference to `zmq_term'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::socket_t::socket_t(zmq::context_t&, int)':
/usr/include/zmq.hpp:251: undefined reference to `zmq_socket'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::socket_t::close()':
/usr/include/zmq.hpp:283: undefined reference to `zmq_close'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::socket_t::connect(char const*)':
/usr/include/zmq.hpp:314: undefined reference to `zmq_connect'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::socket_t::send(zmq::message_t&, int)':
/usr/include/zmq.hpp:321: undefined reference to `zmq_send'
/usr/include/zmq.hpp:324: undefined reference to `zmq_errno'
CMakeFiles/test2.dir/main.cpp.o: In function `zmq::socket_t::recv(zmq::message_t*, int)':
/usr/include/zmq.hpp:331: undefined reference to `zmq_recv'
/usr/include/zmq.hpp:334: undefined reference to `zmq_errno'
Should I set another kind of variable in the CMake file or have I installed the library in a wrong directory? or is there anything else that I should have mentioned? and The system witch I'm working on is Ubuntu 14.04
A cmake config file has been added to libzmq github repository Jan 7, 2017 here.
This is not included in the latest release (4.2.1) yet, but I belive it should be in the next release.
I have installed the head version using cmake and then installed cppzmq, which uses
find_package(ZeroMQ REQUIRED)
to locate libzmq. All worked like a charm.EDIT: The cmake config file is included in release 4.2.2 here. Then it was moved to directory
builds/cmake
at release 4.2.4. I didn't test it again butfind_package(ZeroMQ REQUIRED)
should just work since ibzmq 4.2.2.This works as well
CMake doesn't include direct support for 0mq and 0mq doesn't include direct support for CMake. But, 0mq does support
pkg-config
and we can use this to help us. Since you mentioned that you're on Ubuntu 14.04, make sure you've donesudo apt-get install libzmq3-dev
to install the 0mq libraries, headers, and thepkg-config
.pc
file.Then use the following
CMakeLists.txt
which I've modified from your version above. (I've commented all my changes inline.)Now you can
make
your project.If you want to see what's happening under the hood, do a verbose make.
If you look at the compile line, you'll notice that
-std=gnu++11
flag)-I/path/to/zmq
flag. That's because Ubuntu dumpszmq.hpp
in to/usr/include
and CMake is smart enough to know that is a default path, so it does nothingIf you look at the link line, you'll notice that libzmq.so has been included via it's full path. Some people don't like that (myself included) and prefer
-L/lib/dir -lmylib
instead. Using the full path is "the CMake way", and you'll actually come to appreciate it as you grow with CMake and use it for larger and more complicated projects (you still might not like it though.)Also note, that since you're on Ubuntu we could have cheated and used
dpkg -L libzmq3-dev
to find the locations of the files we're interested in then added them to your originalCMAKE_CXX_FLAGS
line, but that's cheating and more importantly, not portable.