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ROS2 Messages from IDL Files

asked 2019-06-03 17:48:25 -0600

updated 2019-06-04 20:40:55 -0600

I've seen in the release notes for Dashing that the message generation pipeline now supports IDL files directly. Are there any examples available on how to actually use an IDL file directly in a messages package? Can I pass a list of IDL files directly to rosidl_generate_interfaces()?


Based on the advice of sloretz I've tried creating an example project that includes the MyMessage.idl test case from rosidl_parser. It's located at idl_msgs. It tries to generate messages from a single IDL file. On Ubuntu 18.04 with Dashing, running 'colcon build' on the package produces several errors:

davidhodo@ubuntu:~/devel/idl_test_ws$ colcon build
Starting >>> idl_msgs
--- stderr: idl_msgs
AssertionError in template '/opt/ros/dashing/share/rosidl_generator_cpp/cmake/../resource/msg__struct.hpp.em': unknown primitive type 'long double'
AssertionError when expanding 'idl__struct.hpp.em' into '/home/davidhodo/devel/idl_test_ws/build/idl_msgs/rosidl_generator_cpp/idl_msgs/idl/my_message__struct.hpp': unknown primiti
ve type 'long double'
Error processing idl file: /home/davidhodo/devel/idl_test_ws/src/idl_msgs/idl/MyMessage.idl
TypeError in template '/opt/ros/dashing/share/rosidl_generator_dds_idl/resource/msg.idl.em': %d format: a number is required, not str
TypeError when expanding 'idl.idl.em' into '/home/davidhodo/devel/idl_test_ws/build/idl_msgs/rosidl_generator_dds_idl/idl_msgs/idl/dds_opensplice/MyMessage_.idl': %d format: a numb
er is required, not str
Error processing idl file: /home/davidhodo/devel/idl_test_ws/src/idl_msgs/idl/MyMessage.idl

The full error output is available here.

Any suggestions would be appreciated.


I was able to get it to build with a few modifications. I had to remove the long double and wchar types as well as the includes. I also had to change the top level module name to match my package name and the next level module name from 'msg' to 'idl'.

module idl_msgs{
  module idl {


That compiled and gave me a working message. The updated code is available at:



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Can you try to remove the long double field? The 128 bit floating point type doesn't exist anywhere in the ROS message format and therefore has probably never been tested with the generators.

Dirk Thomas gravatar image Dirk Thomas  ( 2019-06-04 13:40:42 -0600 )edit

If you want to use long doubleyou can try the following two PRs which should make it work with FastRTPS: and

Dirk Thomas gravatar image Dirk Thomas  ( 2019-06-04 14:13:48 -0600 )edit

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answered 2019-06-03 18:07:32 -0600

sloretz gravatar image

The package rosidl_parser has a few test idl files:

The documentation for rosidl_generate_interfaces says IDL files can be passed directly to rosidl_generate_interfaces(). Internally all .action, .msg, and .srv are converted to .idl files before given to the code generators, so for more examples build a message package and look in the build directory for the generated files.

The design page IDL -Interface Definition and Language Mapping documents the subset of OMG IDL 4.2 supported in Dashing.

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You can convert existing .msg files using the following command: ros2 run rosidl_adapter The same exists for .srv files too. In general you only want to do so if you want to leverage some features from .idl which aren't available in .msg / .srv.

Dirk Thomas gravatar image Dirk Thomas  ( 2019-06-03 18:12:19 -0600 )edit

Thanks. I've tried creating a basic package based on those test messages and haven't been able to get it successfully build. Based on Dirk's comment, I might should see if what I'm attempting to do is even possible. My main reason for trying this is to try to get ROS2 to interoperate with another system that is using DDS natively. The IDLs don't contain features that aren't supported in ROS2's IDL subset, but I'm unable to generate .msg files that match them, mostly due to underscores in types and namespaces that are added by the ROS message generation process.

david.hodo gravatar image david.hodo  ( 2019-06-04 09:03:09 -0600 )edit

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Asked: 2019-06-03 17:48:25 -0600

Seen: 2,363 times

Last updated: Jun 04 '19