我刚刚开始学习如何使用zeromq库以及如何在不同的C ++项目中使用它们。我编写的示例代码(实际上是从那里的教程中复制的)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;
}
并通过以下命令构建此文件的输出:
g++ main.cpp -o test -lzmq
该文件将毫无问题地生成。
我遇到的问题是我想使用CMake构建文件。因此,我编写了CMakeLists.txt
如下文件:
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})
我认为足以构建程序的部分是,-lzmq
但是即使包含该部分,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文件中设置其他类型的变量,还是将库安装在错误的目录中?还是我应该提到的其他内容?我正在使用的系统女巫是Ubuntu 14.04
CMake不直接支持0mq,0mq不直接支持CMake。但是,0mq确实支持pkg-config
,我们可以用它来帮助我们。既然您提到您使用的是Ubuntu 14.04,请确保已完成sudo apt-get install libzmq3-dev
安装0mq库,标头和pkg-config
.pc
文件的操作。
然后使用下面CMakeLists.txt
我从您的版本中修改过的以下内容。(我已在线注释了所有更改。)
## 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})
现在您可以进行make
项目了。
❯ make
[ 50%] Building CXX object CMakeFiles/test2.dir/main.cpp.o
[100%] Linking CXX executable test2
[100%] Built target test2
如果您想了解引擎盖下发生的事情,请进行详细说明。
❯ 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
如果您看一下编译行,您会注意到
-std=gnu++11
标志)-I/path/to/zmq
标志。那是因为Ubuntu转储zmq.hpp
到/usr/include
并且CMake很聪明,知道这是默认路径,所以它什么也不做如果查看链接线,您会注意到libzmq.so已通过其完整路径包含在内。有些人不喜欢那样(包括我自己),-L/lib/dir -lmylib
而是喜欢。使用完整路径是“ CMake方式”,随着CMake的发展,您会逐渐体会到它的价值,并将其用于更大,更复杂的项目(尽管您仍然可能不喜欢它)。
还要注意,由于您使用的是Ubuntu,因此我们可能会作弊并用来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CMAKE_CXX_FLAGS
行中,但这是作弊的,更重要的是,它不是可移植的。
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我来说两句