link c code with c++ ROS code
asked 23 hours ago
I am having trouble with linking c-code with C++-code. The C++ code describes a ROS-node. I made a program that can read a compressed image-stream over udp with gstreamer in c-code. Each image-buffer calls a C++-method of the ROS-node, which effectively converts the gstreamer stream into a ROS image stream.
I organised it as such:
- udp_to_ros3.c file that describes gstreamer-functionality,
- ros_cpp.cpp file with class and wrapper for C-code to indirectly call class
- ros_cpp.o.so dynamic library compiled by catkin_make from ros_cpp.cpp (location: /home/edward/catkin_ws/devel/lib/)
- im_imageconv.h header of wrapper-code, used in ros_cpp.cpp and upd_to_ros3.c
I compiled upd_to_ros3.c to upd_to_ros3.o, and ros_cpp.o.so is compiled by catkin_make.
Now try to link it with: gcc -Wall -L/home/edward/catkin_ws/devel/lib/ udp_to_ros3.o -lros_cpp.o $(pkg-config --cflags --libs gstreamer-0.10) -lgstapp-0.10 -o udp_to_ros_image
I get the following errors:
/home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference to cv::fastFree(void*)' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference toros::init(int&, char**, std::basic_string, std::allocator > const&, unsigned int)' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference toros::NodeHandle::~NodeHandle()' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference toimage_transport::ImageTransport::ImageTransport(ros::NodeHandle const&)' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference to ros::Time::now()' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference toimage_transport::Publisher::publish(boost::shared_ptr > const> const&) const' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference toimage_transport::ImageTransport::~ImageTransport()' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference toros::NodeHandle::NodeHandle(std::basic_string, std::allocator > const&, std::map, std::allocator >, std::basic_string, std::allocator >, std::less, std::allocator > >, std::allocator, std::allocator > const, std::basic_string, std::allocator > > > > const&)' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference to cv::waitKey(int)' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference tocv_bridge::CvImage::toImageMsg() const' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference to ros::spinOnce()' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference tocv::Mat::copySize(cv::Mat const&)' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference to cv::Mat::deallocate()' /home/edward/catkin_ws/devel/lib//libros_cpp.o.so: undefined reference toimage_transport::ImageTransport::advertise(std::basic_string, std::allocator > const&, unsigned int, bool)' collect2: ld returned 1 exit status
I think it needs the ROS-headerfiles, but maybe also the libraries (?) as used by catkin to be able to link the two files. But even when I add -I/opt/ros/groovy/include/ros/ it still complains about undefined reference to ros:: things.
How to solve this the most pragmatic? Do I need to compile also the C-file within catkin CMakefile and link them together, or is there another way ?
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2 Answers
answered 19 hours ago
To answer your last question, you do not necessarily need to compile your standalone (in the sense of ROS independent) c code within catkin. It is pretty straight forward to compile your c code as a shared or static library, and then link your ROS node to it using the standard CMake syntax (by adding your c library to target_link_libraries(...) for example).
To address your linker errors. You are not missing header files, you are improperly specify the libraries to link to and the library search paths. Remember that "-L" specifies the search path, and the "-l" specifies the library name (preferably without path and without ending). For object files ".o" you do not need the "-l" flag prefix. you are missing lots of opencv libraries in command, you can try adding "-lopencv_core" and "-lcv_bridge -limage_transport" to take care of the missing OpenCV and OpenCV binding symbols.
But I highly recommend you use the cakin for building and integrating your ROS code, and not to build things by hand.
EDIT: Responding to your further comments, you are using the CMake commands incorrectly. To create your library and link to it in CMake you should use:
add_library(upd_to_ros SHARED src/upd_to_ros3.cpp) #add the source files for your "external" library code here
add_executable(imageconv_node src/ros_cpp.cpp )
target_link_libraries(imageconv_node
upd_to_ros
${catkin_LIBRARIES}
)
Note that your ROS node imageconv_node declared in your CMakeLists.txt will need a typical main function, and it is bad practice to hard code full paths in a CMakeLists.txt.
Comments
I also tried it by hand , compiled : gcc -Wall upd_to_ros3.o -o udp_to_ros_image -L/home/edward/catkin_ws/devel/lib/ -lros_cpp.o $(pkg-config --cflags --libs gstreamer-0.10) -lgstapp-0.10 -lopencv_core -L/opt/ros/groovy/lib/ -lrostime -limage_transport -lcv_bridge -lopencv_highgui This was successful.
edward (13 hours ago)
answered 14 hours ago
Thank you for your answer Jensenb. In the catkin CMakeList.txt I declared the following:
add_executable(imageconv_node src/ros_cpp.cpp ) <-- br="" has="" is="" it="" library="" main="" nbsp="" no="" really="" the="" which="">target_link_libraries(
/home/edward/c920/upd_to_ros3.o<-- before="" br="" compiled="">${catkin_LIBRARIES}
)
Then get the following error:
CMake Error at CMakeLists.txt:115 (target_link_libraries): Cannot specify link libraries for target "/home/edward/c920/upd_to_ros3.o" which is not built by this project.
How to continue?
Comments
Please do not answers to your question that are not answers but further questions. Instead either edit your original question, or post a comment to my answer. You should delete this post.
jensenb (38 mins ago)
