Question

我刚刚开始学习如何使用zeromq库并在不同的C ++项目中使用它们。我写的示例代码（实际上从那里复制了教程）是这样的：

//  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;
}

并使用以下命令构建此文件的输出：

g++ main.cpp -o test -lzmq

生成文件没有问题。

我遇到的问题是我想使用CMake构建文件。因此，我已经编写了CMakeLists.txt文件，如下所示：

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})

我认为构建程序的部分是-lzmq，但即使包含该部分，我也会收到以下错误消息：

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'

我应该在CMake文件中设置另一种变量，还是将库安装在错误的目录中？或者还有什么我应该提到的吗？我正在研究的系统是Ubuntu 14.04

Answer 1

CMake不包括对0mq的直接支持，0mq不包括对CMake的直接支持。但是，0mq确实支持pkg-config，我们可以用它来帮助我们。由于您提到您使用的是Ubuntu 14.04，因此请确保您已完成sudo apt-get install libzmq3-dev以安装0mq库，标头和pkg-config .pc文件。

然后使用我在上面的版本中修改过的CMakeLists.txt。（我已对内线的所有更改进行了评论。）

## i have cmake 3.5
cmake_minimum_required(VERSION 3.5)
project(test2)

## use this to globally use C++11 with in our project
set(CMAKE_CXX_STANDARD 11)

## load in pkg-config support
find_package(PkgConfig)
## use pkg-config to get hints for 0mq locations
pkg_check_modules(PC_ZeroMQ QUIET zmq)

## use the hint from above to find where 'zmq.hpp' is located
find_path(ZeroMQ_INCLUDE_DIR
        NAMES zmq.hpp
        PATHS ${PC_ZeroMQ_INCLUDE_DIRS}
        )

## use the hint from about to find the location of libzmq
find_library(ZeroMQ_LIBRARY
        NAMES zmq
        PATHS ${PC_ZeroMQ_LIBRARY_DIRS}
        )

set(SOURCE_FILES main.cpp)
add_executable(test2 ${SOURCE_FILES})

## add the include directory to our compile directives
target_include_directories(test2 PUBLIC ${ZeroMQ_INCLUDE_DIR})
## at the 0mq library to our link directive
target_link_libraries(test2 PUBLIC ${ZeroMQ_LIBRARY})

现在你可以make你的项目。

❯ make
[ 50%] Building CXX object CMakeFiles/test2.dir/main.cpp.o
[100%] Linking CXX executable test2
[100%] Built target test2

如果你想看看幕后发生了什么，请做一个详细的制作。

❯ make VERBOSE=1
/usr/bin/cmake -H/home/nega/foo -B/home/nega/foo/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake -E cmake_progress_start /home/nega/foo/build/CMakeFiles /home/nega/foo/build/CMakeFiles/progress.marks
make -f CMakeFiles/Makefile2 all
make[1]: Entering directory '/home/nega/foo/build'
make -f CMakeFiles/test2.dir/build.make CMakeFiles/test2.dir/depend
make[2]: Entering directory '/home/nega/foo/build'
cd /home/nega/foo/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/nega/foo /home/nega/foo /home/nega/foo/build /home/nega/foo/build /home/nega/foo/build/CMakeFiles/test2.dir/DependInfo.cmake --color=
make[2]: Leaving directory '/home/nega/foo/build'
make -f CMakeFiles/test2.dir/build.make CMakeFiles/test2.dir/build
make[2]: Entering directory '/home/nega/foo/build'
[ 50%] Building CXX object CMakeFiles/test2.dir/main.cpp.o
/usr/bin/c++     -std=gnu++11 -o CMakeFiles/test2.dir/main.cpp.o -c /home/nega/foo/main.cpp
[100%] Linking CXX executable test2
/usr/bin/cmake -E cmake_link_script CMakeFiles/test2.dir/link.txt --verbose=1
/usr/bin/c++      CMakeFiles/test2.dir/main.cpp.o  -o test2 /usr/lib/x86_64-linux-gnu/libzmq.so 
make[2]: Leaving directory '/home/nega/foo/build'
[100%] Built target test2
make[1]: Leaving directory '/home/nega/foo/build'
/usr/bin/cmake -E cmake_progress_start /home/nega/foo/build/CMakeFiles 0

如果查看编译行，您会注意到

添加了C ++ 11支持（带有-std=gnu++11标志）
没有-I/path/to/zmq标志。这是因为Ubuntu将zmq.hpp转储到/usr/include，而CMake足够聪明，知道这是一条默认路径，所以它什么都不做

如果查看链接行，您会注意到libzmq.so已经通过它的完整路径包含在内。有些人不喜欢（包括我自己），而更喜欢-L/lib/dir -lmylib。使用完整路径是“CMake方式”，当你与CMake一起成长并将其用于更大更复杂的项目时，你会真正体会到它（你仍然可能不喜欢它。）

另请注意，由于您使用的是Ubuntu，我们可能会欺骗并使用dpkg -L libzmq3-dev查找我们感兴趣的文件的位置，然后将它们添加到原始的CMAKE_CXX_FLAGS行，但是这是作弊，更重要的是，不便携。

Answer 2

cmake配置文件已添加到libzmq github存储库2017年1月7日here。

这还没有包含在最新版本（4.2.1）中，但我相信它应该在下一个版本中。

我已经使用cmake安装了head版本，然后安装了cppzmq，它使用find_package(ZeroMQ REQUIRED)来定位libzmq。一切都像魅力一样。

编辑：cmake配置文件包含在版本4.2.2 here中。然后它在版本4.2.4移动到目录builds/cmake。我没有再次测试它，但{i}只能在ibzmq 4.2.2之后才能正常工作。

Answer 3

这也很好

 cmake_minimum_required(VERSION 3.6)
 project(test)     
 add_executable(c main.cpp)
 target_link_libraries(c zmq)

如何在cmake中导入zeromq库？

3 个答案: