ROS Answers SE migration: ROS2 Linking

Question

I'm having trouble linking libraries in ROS2. I have a simple example posted here

I have two packages. awesome_library defines a C++ class in a library and fantastic_node defines a C++ executable that instantiates the class from awesome_library.

I am familiar with how to do this in ROS1, but in ROS2 I am getting the following error.

[ 50%] Linking CXX executable fantastic_node_node
CMakeFiles/fantastic_node_node.dir/src/fnode.cpp.o: In function `main':
fnode.cpp:(.text+0x17d): undefined reference to `awesome_library::Awesomeness::Awesomeness()'
collect2: error: ld returned 1 exit status
CMakeFiles/fantastic_node_node.dir/build.make:177: recipe for target 'fantastic_node_node' failed
make[2]: *** [fantastic_node_node] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/fantastic_node_node.dir/all' failed

From the command ament build --only-packages awesome_library fantastic_node

I've tried a couple different variations of the library installation in awesome_library and target linking in fantastic_node but have not found one that works, or a similar example.

Current attempts with allenh1's branch:

ros-bouncy-ament-tools:
  Installed: 0.5.0-0bionic.20180719.223430
  Candidate: 0.5.0-0bionic.20180719.223430
  Version table:
 *** 0.5.0-0bionic.20180719.223430 500
        500 http://repo.ros2.org/ubuntu/main bionic/main amd64 Packages
        100 /var/lib/dpkg/status
! ros2_ws/ > apt-cache policy python3-colcon-core 
python3-colcon-core:
  Installed: 0.3.12-1
  Candidate: 0.3.12-1
  Version table:
 *** 0.3.12-1 500
        500 http://repo.ros2.org/ubuntu/main bionic/main amd64 Packages
        500 http://repo.ros2.org/ubuntu/main bionic/main arm64 Packages
        100 /var/lib/dpkg/status
! ros2_ws/ > colcon build --packages-select awesome_library fantastic_node --symlink-install
Starting >>> awesome_library
Finished <<< awesome_library [0.27s]                       
Starting >>> fantastic_node
--- stderr: fantastic_node                             
CMakeFiles/fantastic_node_node.dir/src/fnode.cpp.o: In function `main':
fnode.cpp:(.text+0x17d): undefined reference to `awesome_library::Awesomeness::Awesomeness()'
collect2: error: ld returned 1 exit status
make[2]: *** [fantastic_node_node] Error 1
make[1]: *** [CMakeFiles/fantastic_node_node.dir/all] Error 2
make: *** [all] Error 2
---
Failed   <<< fantastic_node [ Exited with code 2 ]

Summary: 1 package finished [0.75s]
  1 package failed: fantastic_node
  1 package had stderr output: fantastic_node
[0.860s] ERROR:colcon.colcon_notification.desktop_notification:Exception in desktop notification extension 'notify2': org.freedesktop.Notifications.MaxNotificationsExceeded: Exceeded maximum number of notifications
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/colcon_notification/desktop_notification/__init__.py", line 107, in notify
    title=title, message=message, icon_path=icon_path)
  File "/usr/lib/python3/dist-packages/colcon_notification/desktop_notification/notify2.py", line 50, in notify
    self._last_notification.show()
  File "/usr/lib/python3/dist-packages/notify2.py", line 188, in show
    self.timeout,  # expire_timeout
  File "/usr/lib/python3/dist-packages/dbus/proxies.py", line 70, in __call__
    return self._proxy_method(*args, **keywords)
  File "/usr/lib/python3/dist-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib/python3/dist-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)
dbus.exceptions.DBusException: org.freedesktop.Notifications.MaxNotificationsExceeded: Exceeded maximum number of notifications

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Originally posted by David Lu on ROS Answers with karma: 10932 on 2018-11-01

Post score: 1

---

Original comments

Comment by gvdhoorn on 2018-11-01:
Unfortunately, GHFM doesn't work here :(

Answer 1

you should probably use colcon if you're using bouncy:

colcon build --packages-select awesome_library fantastic_node

---

Edit: upon further review, I see you're linking to ${catkin_LIBRARIES}, which you probably shouldn't be doing.

In my ports, I usually do a

set(req_deps
  "rclcpp"
  # other libs
)

then, in lieu of ${catkin_LIBRARIES}, I would do this:

ament_auto_find_build_dependencies(REQUIRED ${req_deps})

and this

ament_auto_add_library(awesomeness src/aswesome.cpp)
ament_target_dependencies(awesomeness ${req_deps})

For an example of libraries, I'll point you to my openslam_gmapping port, and for a very minimal port (so you can see the whole diff), I'll point you to a port of rplidar_ros I did recently.

I'm sure I forgot something above, so let me know what it was. ;)

---

Originally posted by allenh1 with karma: 3055 on 2018-11-01

This answer was ACCEPTED on the original site

Post score: 1

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Original comments

Comment by David Lu on 2018-11-01:
That results in the same error.

Comment by allenh1 on 2018-11-01:
Ya, noticed a bit more for you to change, haha. See above.

Comment by David Lu on 2018-11-01:
Okay, I've tried porting to ament_auto (of which there are few examples/documents that I've found). Results are in this branch: https://github.com/DLu/simple_ros2_example/tree/ros2auto Still gets the same linking error.

Comment by allenh1 on 2018-11-02:
Hey! I just went ahead and played around with it some. PR is on your repo, linked here for convenience.

Comment by David Lu on 2018-11-02:
I tried your branch and it didn't work (see comments on the PR). It also seems like there should be a way to do it without ament_auto (since the migration guide and examples don't use it)

Comment by allenh1 on 2018-11-02:\

I tried your branch and it didn't work

:( It definitely worked on my machine. Did you invoke colcon with --symlink-install?

do it without ament_auto

that makes sense. @dirk-thomas can you please explain what ament_auto is? I've forgotten the difference.

Comment by allenh1 on 2018-11-02:
Also, I didn't see the PR comments...

Comment by David Lu on 2018-11-02:
Oops, forgot to submit my review. Done now.

I've updated the above with some of the pertinent version info, exact command and output.

Comment by David Lu on 2018-11-02:
Any hints @dirk-thomas?