ROS2 建立 workapace , package node , build 範例說明

 下面給你「一步到位」的順序＋可直接複製的範例（含 Python/C++ 兩種做法）。

範例使用工作區名：~/ros2_ws_demo，套件名：my_pkg.

1) 建立 Workspace

# 建立目錄結構
mkdir -p ~/ros2_ws_demo/src
cd ~/ros2_ws_demo

# 只載入系統 ROS 2
source /opt/ros/humble/setup.bash

2A) 建立 Python 套件 (rclpy)

cd ~/ros2_ws_demo/src
ros2 pkg create my_pkg --build-type ament_python --dependencies rclpy std_msgs

最小節點（my_pkg/my_pkg/talker.py）：

#!/usr/bin/env python3
import rclpy
from rclpy.node import Node
from std_msgs.msg import String

class Talker(Node):
    def __init__(self):
        super().__init__('talker')
        self.pub = self.create_publisher(String, 'chatter', 10)
        self.create_timer(0.5, self.tick)

    def tick(self):
        msg = String(); msg.data = 'hello ros2'
        self.pub.publish(msg)

def main():
    rclpy.init(); rclpy.spin(Talker()); rclpy.shutdown()
if __name__ == '__main__': main()

在 setup.py 的 entry_points 增加（已自帶，補一行即可）：

'console_scripts': [
    'talker = my_pkg.talker:main',
],

2B) 建立 C++ 套件 (rclcpp)

cd ~/ros2_ws_demo/src
ros2 pkg create my_pkg_cpp --build-type ament_cmake --dependencies rclcpp std_msgs

最小節點（my_pkg_cpp/src/talker.cpp）：

#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"
using std::placeholders::_1;

int main(int argc, char** argv){
  rclcpp::init(argc, argv);
  auto node = rclcpp::Node::make_shared("talker_cpp");
  auto pub = node->create_publisher<std_msgs::msg::String>("chatter", 10);
  rclcpp::WallTimer<std::chrono::milliseconds> *timer;
  timer = new rclcpp::WallTimer<std::chrono::milliseconds>(
      std::chrono::milliseconds(500),
      [pub](){
        auto msg = std_msgs::msg::String();
        msg.data = "hello ros2";
        pub->publish(msg);
      });
  node->create_wall_timer(std::chrono::milliseconds(500), [pub](){
    auto msg = std_msgs::msg::String(); msg.data = "hello ros2"; pub->publish(msg);
  });
  rclcpp::spin(node); rclcpp::shutdown(); return 0;
}

在 my_pkg_cpp/CMakeLists.txt 增加可執行檔與安裝：

add_executable(talker src/talker.cpp)
ament_target_dependencies(talker rclcpp std_msgs)
install(TARGETS talker DESTINATION lib/${PROJECT_NAME})

3)（可選）建立 Launch

~/ros2_ws_demo/src/my_pkg/launch/demo.launch.py

from launch import LaunchDescription
from launch_ros.actions import Node
def generate_launch_description():
    return LaunchDescription([
        Node(package='my_pkg', executable='talker', name='talker_py'),
        # Node(package='my_pkg_cpp', executable='talker', name='talker_cpp'), # 若用 C++
    ])

4) 建置

cd ~/ros2_ws_demo
colcon build --symlink-install

5) 載入環境

source install/setup.bash

6) 執行與檢查

# 直接跑節點
ros2 run my_pkg talker              # Python
# ros2 run my_pkg_cpp talker       # C++

# 或用 launch
ros2 launch my_pkg demo.launch.py

# 檢查
ros2 node list
ros2 topic echo /chatter

小提示

• 每次更動程式後：colcon build → source install/setup.bash。

• 若有多個 workspace，確保最後 source 的是你要用的那個。

• 新增相依套件：rosdep install -i --from-paths src -y。