如何在cmake中导入zeromq库？

我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(实际上是从教程中复制的)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,我编写了一个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

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.既然你提到你在Ubuntu 14.04上,请确保你已经完成了sudo apt-get install libzmq3-dev来安装0mq库,头文件和pkg-config .pc文件.

然后使用我从上面的版本修改过的以下CMakeLists.txt. (我已经评论了我的所有内联更改.)

## 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})

现在你可以制作你的项目了.

❯ 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

如果你看一下编译行,你会发现它

>添加了C 11支持(使用-std = gnu 11标志)

>没有-I / path / to / zmq标志.那是因为Ubuntu将zmq.hpp转储到/usr/include中,并且CMake足够聪明,知道这是一个默认路径,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.)

还要注意,既然你在Ubuntu上我们可以欺骗并使用dpkg -L libzmq3-dev来查找我们感兴趣的文件的位置,然后将它们添加到你原来的CMAKE_CXX_FLAGS行,但这是作弊,更重要的是,不便携.