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I had tested ros2 launch with arguments. The arguments are successfully implemented using only set LaunchConfiguration exclude DeclareLaunchArgument. For example, attached launch files worked excluding DeclareLaunchArgument

import os

from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.substitutions import LaunchConfiguration, EnvironmentVariable
from launch.actions import DeclareLaunchArgument
from launch_ros.actions import Node

TURTLEBOT3_MODEL = os.environ['TURTLEBOT3_MODEL']

def generate_launch_description():
    use_sim_time = LaunchConfiguration('use_sim_time', default='false')
    urdf_file_name = 'turtlebot3_' + TURTLEBOT3_MODEL + '.urdf'
    print("urdf_file_name : {}".format(urdf_file_name))

    urdf = os.path.join(get_package_share_directory('turtlebot3_description'), 'urdf', urdf_file_name)

    return LaunchDescription([
        #DeclareLaunchArgument(
        #    'use_sim_time',
        #    default_value='false',
        #    description='Use simulation (Gazebo) clock if true'),

        Node(
            package='robot_state_publisher',
            node_executable='robot_state_publisher',
            node_name='robot_state_publisher',
            output='screen',
            parameters=[{' use_sim_time': use_sim_time}],
            arguments=[urdf]),
    ])

However, most examples of ros2 launch are included DeclareLaunchArgument when user want to use arguments. So, my main questions is What is different btw LaunchConfiguration and DeclareLaunchArgument?

Hi, Kaveh :) You can make a new node whose laserscan publisher combined data and it subscribes laserscan and ultrasonic

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Thank you for updates. I could check launch arguments using -s and I clearly understand what is a different of them. Tha

Thank you for comments :) However, if I set LaunchConfiguration excluding DeclareLaunchArgument, I would access launch a

[ROS2] what is different between DeclareLaunchArgument and LaunchConfiguration I had tested ros2 launch with arguments.

[ROS2] what is different between DeclareLaunchArgument and LaunchConfiguration I had tested ros2 launch with arguments.

Hello :)

I have tried to install ROS2 in my macbook(High Sierra). But I got an error message that rosidl_generator_c package in rosidl(master branch) is failed to build. In this error was not occured in ubuntu.

How to handle this problem?

--- stderr: rosidl_generator_c                                                                                  
'Token' object has no attribute 'children' 
/Users/darby/ros2_ws/build/rosidl_generator_c/rosidl_adapter/rosidl_generator_c/msg/BoundedArrayPrimitives.idl
Error processing idl file: 
/Users/darby/ros2_ws/build/rosidl_generator_c/rosidl_adapter/rosidl_generator_c/msg/BoundedArrayPrimitives.idl
Traceback (most recent call last):
  File "/Users/darby/ros2_ws/src/ros2/rosidl/rosidl_generator_c/bin/rosidl_generator_c", line 40, in <module>
sys.exit(main())
  File "/Users/darby/ros2_ws/src/ros2/rosidl/rosidl_generator_c/bin/rosidl_generator_c", line 35, in main
    args.generator_arguments_file,
   File "/Users/darby/ros2_ws/src/ros2/rosidl/rosidl_generator_c/rosidl_generator_c/__init__.py", line 35, in generate_c
    generate_files(generator_arguments_file, mapping)
  File "/Users/darby/ros2_ws/install/rosidl_cmake/lib/python3.7/site-packages/rosidl_cmake/__init__.py", line 121, in 
generate_files
    raise(e)
  File "/Users/darby/ros2_ws/install/rosidl_cmake/lib/python3.7/site-packages/rosidl_cmake/__init__.py", line 101, in 
generate_files
    idl_file = parse_idl_file(locator)
  File "/Users/darby/ros2_ws/install/rosidl_parser/lib/python3.7/site-packages/rosidl_parser/parser.py", line 60, in 
parse_idl_file
    content = parse_idl_string(string, png_file=png_file)
  File "/Users/darby/ros2_ws/install/rosidl_parser/lib/python3.7/site-packages/rosidl_parser/parser.py", line 69, in 
parse_idl_string
    content = extract_content_from_ast(tree)
  File "/Users/darby/ros2_ws/install/rosidl_parser/lib/python3.7/site-packages/rosidl_parser/parser.py", line 139, in 
extract_content_from_ast
    add_message_members(msg, struct_defs[0])
  File "/Users/darby/ros2_ws/install/rosidl_parser/lib/python3.7/site-packages/rosidl_parser/parser.py", line 366, in 
add_message_members
    abstract_type = get_abstract_type_from_type_spec(type_spec)
  File "/Users/darby/ros2_ws/install/rosidl_parser/lib/python3.7/site-packages/rosidl_parser/parser.py", line 407, in 
get_abstract_type_from_type_spec
    return get_abstract_type(child)
  File "/Users/darby/ros2_ws/install/rosidl_parser/lib/python3.7/site-packages/rosidl_parser/parser.py", line 440, in 
get_abstract_type
    basetype = get_abstract_type_from_type_spec(type_spec)
  File "/Users/darby/ros2_ws/install/rosidl_parser/lib/python3.7/site-packages/rosidl_parser/parser.py", line 407, in 
get_abstract_type_from_type_spec
    return get_abstract_type(child)
  File "/Users/darby/ros2_ws/install/rosidl_parser/lib/python3.7/site-packages/rosidl_parser/parser.py", line 416, in 
get_abstract_type
    while len(child.children) == 1:
AttributeError: 'Token' object has no attribute 'children'
make[2]: *** [rosidl_generator_c/rosidl_generator_c/msg/bool.h] Error 1
make[2]: *** Deleting file `rosidl_generator_c/rosidl_generator_c/msg/bool.h'
make[1]: *** [CMakeFiles/rosidl_generator_c_interfaces__rosidl_generator_c.dir/all] Error 2
make: *** [all] Error 2
---
Failed   <<< rosidl_generator_c [ Exited with code 2 ]

Thank you very much!

Build failed at rosidl_generator_c package Hello :) I have tried to install ROS2 in my macbook(High Sierra). But I got

I assume that you could somthing wrong to add publisher on your code. Can you attach your code?

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