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Background: I work in underwater robotics, and DCCL is a library for encoding of messages to fit within our extremely constrained message sizes based on an original protobuf format. Just for practice before applying this to one of our real messages, I'm modifying the basic publisher/subscriber from the tutorial to encode the message to DCCL before sending. It seems to do just fine with the protobuf library, but I'm getting an undefined reference error on the DCCL library, which I assuming is a linking error.

Error:

teddybouch@Norby:~/workspace/ros2_ws$ colcon build --packages-select cpp_pubsub
Starting >>> cpp_pubsub
--- stderr: cpp_pubsub                             
/usr/bin/ld: CMakeFiles/talker.dir/src/publisher_member_function.cpp.o: in function `MinimalPublisher::timer_callback()':
publisher_member_function.cpp:(.text._ZN16MinimalPublisher14timer_callbackEv[_ZN16MinimalPublisher14timer_callbackEv]+0xa2): undefined reference to `dccl::Codec::Codec(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/usr/bin/ld: publisher_member_function.cpp:(.text._ZN16MinimalPublisher14timer_callbackEv[_ZN16MinimalPublisher14timer_callbackEv]+0xed): undefined reference to `testdccl::NavigationReport::NavigationReport()'
/usr/bin/ld: publisher_member_function.cpp:(.text._ZN16MinimalPublisher14timer_callbackEv[_ZN16MinimalPublisher14timer_callbackEv]+0x1d5): undefined reference to `dccl::Codec::encode(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, google::protobuf::Message const&, bool, int)'
/usr/bin/ld: publisher_member_function.cpp:(.text._ZN16MinimalPublisher14timer_callbackEv[_ZN16MinimalPublisher14timer_callbackEv]+0x3b7): undefined reference to `testdccl::NavigationReport::~NavigationReport()'
/usr/bin/ld: publisher_member_function.cpp:(.text._ZN16MinimalPublisher14timer_callbackEv[_ZN16MinimalPublisher14timer_callbackEv]+0x3c6): undefined reference to `dccl::Codec::~Codec()'
/usr/bin/ld: publisher_member_function.cpp:(.text._ZN16MinimalPublisher14timer_callbackEv[_ZN16MinimalPublisher14timer_callbackEv]+0x48b): undefined reference to `testdccl::NavigationReport::~NavigationReport()'
/usr/bin/ld: publisher_member_function.cpp:(.text._ZN16MinimalPublisher14timer_callbackEv[_ZN16MinimalPublisher14timer_callbackEv]+0x4a3): undefined reference to `dccl::Codec::~Codec()'
/usr/bin/ld: CMakeFiles/talker.dir/src/publisher_member_function.cpp.o: in function `void dccl::Codec::load<testdccl::NavigationReport>()':
publisher_member_function.cpp:(.text._ZN4dccl5Codec4loadIN8testdccl16NavigationReportEEEvv[_ZN4dccl5Codec4loadIN8testdccl16NavigationReportEEEvv]+0x11): undefined reference to `testdccl::NavigationReport::descriptor()'
/usr/bin/ld: publisher_member_function.cpp:(.text._ZN4dccl5Codec4loadIN8testdccl16NavigationReportEEEvv[_ZN4dccl5Codec4loadIN8testdccl16NavigationReportEEEvv]+0x28): undefined reference to `dccl::Codec::load(google::protobuf::Descriptor const*, int)'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/talker.dir/build.make:132: talker] Error 1
make[1]: *** [CMakeFiles/Makefile2:82: CMakeFiles/talker.dir/all] Error 2
make: *** [Makefile:141: all] Error 2
---
Failed   <<< cpp_pubsub [0.97s, exited with code 2]

Summary: 0 packages finished [1.16s]
  1 package failed: cpp_pubsub
  1 package had stderr output: cpp_pubsub

Except for the addition of the proto directory and the protobuf message definition file in it, I think that the only relevant changes are in the CMakeLists.txt and publisher_member_function.cpp, which I'm including below, but if I've missed something or anyone wants all the code for some reason, the whole package is on my Dropbox here.

CMakeLists.txt:

cmake_minimum_required(VERSION 3.5)
project(cpp_pubsub)

# Default to C99
if(NOT CMAKE_C_STANDARD)
  set(CMAKE_C_STANDARD 99)
endif()

# Default to C++14
if(NOT CMAKE_CXX_STANDARD)
  set(CMAKE_CXX_STANDARD 14)
endif()

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()

# find dependencies
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)
find_package(dccl REQUIRED)
message(STATUS "Using DCCL in ${DCCL_DIR}")
find_package(Protobuf REQUIRED)

if(NOT DEFINED DCCL_INCLUDE_DIR)
  #for DCCL 3.0.3 and newer
  get_target_property(DCCL_INCLUDE_DIR dccl INTERFACE_INCLUDE_DIRECTORIES)
endif()

if(DCCL_INCLUDE_DIR)
  message ...

I'm trying to define a simple message for a larger suite of messages that just defines the limits of some attribute by containing a maximum and a minimum value. So I defined the following message as Limits.msg:

float32 minimum
float32 maximum

The CMakeLists.txt is very simple right now while I debug this issue:

cmake_minimum_required(VERSION 2.8.3)
project(test_msgs)

find_package(catkin REQUIRED
  COMPONENTS
    std_msgs
    message_generation
)

add_message_files(
  FILES
  Limits.msg
  GPSFix.msg
)

generate_messages(
  DEPENDENCIES
  std_msgs
)

catkin_package(
  CATKIN_DEPENDS
  std_msgs
)

I'm keeping GPSFix.msg in there because it's another simple message that builds just fine for some reason. In any case, if I catkin_make from the catkin workspace, I get this:

ava@3b97b310abf0:~/workspace/test_msgs$ catkin_make
Base path: /home/ava/workspace/test_msgs
Source space: /home/ava/workspace/test_msgs/src
Build space: /home/ava/workspace/test_msgs/build
Devel space: /home/ava/workspace/test_msgs/devel
Install space: /home/ava/workspace/test_msgs/install
####
#### Running command: "cmake /home/ava/workspace/test_msgs/src -DCATKIN_DEVEL_PREFIX=/home/ava/workspace/test_msgs/devel -DCMAKE_INSTALL_PREFIX=/home/ava/workspace/test_msgs/install -G Unix Makefiles" in "/home/ava/workspace/test_msgs/build"
####
-- Using CATKIN_DEVEL_PREFIX: /home/ava/workspace/test_msgs/devel
-- Using CMAKE_PREFIX_PATH: /home/ava/workspace/sci288ava/devel;/home/ava/workspace/ava_ros/devel;/home/ava/workspace/ros_ivp/devel;/opt/ros/kinetic;/home/ava/CMake/Modules/
-- This workspace overlays: /home/ava/workspace/sci288ava/devel;/home/ava/workspace/ava_ros/devel;/home/ava/workspace/ros_ivp/devel;/opt/ros/kinetic
-- Using PYTHON_EXECUTABLE: /usr/bin/python
-- Using Debian Python package layout
-- Using empy: /usr/bin/empy
-- Using CATKIN_ENABLE_TESTING: ON
-- Call enable_testing()
-- Using CATKIN_TEST_RESULTS_DIR: /home/ava/workspace/test_msgs/build/test_results
-- Found gmock sources under '/usr/src/gmock': gmock will be built
-- Found gtest sources under '/usr/src/gmock': gtests will be built
-- Using Python nosetests: /usr/bin/nosetests-2.7
-- catkin 0.7.14
-- BUILD_SHARED_LIBS is on
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- ~~  traversing 1 packages in topological order:
-- ~~  - test_msgs
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- +++ processing catkin package: 'test_msgs'
-- ==> add_subdirectory(test_msgs/test_msgs)
-- Using these message generators: gencpp;geneus;genlisp;gennodejs;genpy
/opt/ros/kinetic/share/genmsg/cmake/pkg-genmsg.cmake.em:56: error: <class 'genmsg.base.InvalidMsgSpec'>: /home/ava/workspace/test_msgs/src/test_msgs/test_msgs/msg/Limits.msg: Invalid declaration: float32 minimum
Traceback (most recent call last):
  File "/usr/bin/empy", line 3302, in <module>
    if __name__ == '__main__': main()
  File "/usr/bin/empy", line 3300, in main
    invoke(sys.argv[1:])
  File "/usr/bin/empy", line 3283, in invoke
    interpreter.wrap(interpreter.file, (file, name))
  File "/usr/bin/empy", line 2295, in wrap
    self.fail(e)
  File "/usr/bin/empy", line 2284, in wrap
    callable(*args)
  File "/usr/bin/empy", line 2359, in file
    self.safe(scanner, done, locals)
  File "/usr/bin/empy", line 2401, in safe
    self.parse(scanner, locals)
  File "/usr/bin/empy", line 2421, in parse
    token.run(self, locals)
  File "/usr/bin/empy", line 1425, in run
    interpreter.execute(self.code, locals)
  File "/usr/bin/empy", line 2595, in execute
    _exec(statements, self.globals, locals)
  File "/usr/bin/empy", line 42, in _exec
    exec("""exec code in globals""")
  File "<string>", line 1, in <module>
  File "<string> ...