第2章：ROS 2 核心编程基础

my_robot_pkg/                     # 包根目录
├── package.xml                   # 包元数据和依赖
├── CMakeLists.txt                # 编译与安装规则
├── src/
│   └── my_node.cpp               # C++ 节点代码
├── launch/
│   └── demo.launch.py            # ROS 2 Launch 文件
└── test/                         # 测试代码

source ~/.config/ros2-course-com260/env.bash
mkdir -p ~/my_robot_com260_ws/src
cd ~/my_robot_com260_ws/src
ros2 pkg create my_robot_pkg --build-type ament_cmake --dependencies rclcpp std_msgs
mkdir -p my_robot_pkg/launch

<?xml version="1.0"?>
<package format="3">
  <name>my_robot_pkg</name>
  <version>0.1.0</version>
  <description>My first ROS 2 C++ package</description>
  <maintainer email="student@example.com">Student Name</maintainer>
  <license>Apache-2.0</license>
  <buildtool_depend>ament_cmake</buildtool_depend>
  <depend>rclcpp</depend>
  <depend>std_msgs</depend>
  <test_depend>ament_copyright</test_depend>
  <test_depend>ament_lint_auto</test_depend>
  <export><build_type>ament_cmake</build_type></export>
</package>

cmake_minimum_required(VERSION 3.10)
project(my_robot_pkg)
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)
add_executable(my_node src/my_node.cpp)
target_compile_features(my_node PUBLIC cxx_std_17)
ament_target_dependencies(my_node rclcpp std_msgs)
install(TARGETS my_node DESTINATION lib/${PROJECT_NAME})
install(DIRECTORY launch DESTINATION share/${PROJECT_NAME})
ament_package()

#include <chrono>
#include <memory>
#include "rclcpp/rclcpp.hpp"
 
class MyFirstNode : public rclcpp::Node
{
public:
  MyFirstNode() : Node("my_first_node")
  {
    timer_ = create_wall_timer(std::chrono::seconds(1), [this]() {
      RCLCPP_INFO(get_logger(), "Hello ROS 2! Count: %d", ++count_);
    });
    RCLCPP_INFO(get_logger(), "节点已启动！");
  }
private:
  int count_{0};
  rclcpp::TimerBase::SharedPtr timer_;
};
 
int main(int argc, char ** argv)
{
  rclcpp::init(argc, argv);
  auto node = std::make_shared<MyFirstNode>();
  rclcpp::spin(node);
  node.reset();
  rclcpp::shutdown();
  return 0;
}

// 方式 1：直接创建带命名空间的节点
// 所需头文件：<memory> 和 "rclcpp/rclcpp.hpp"
auto newnode = std::make_shared<rclcpp::Node>("node_name", "my_ns");
 
// 方式 2：命令行重映射
// ros2 run my_robot_pkg my_node --ros-args -r __ns:=/new_ns -r __node:=new_name
 
// 方式 3：在派生类构造函数中指定
class MyNode : public rclcpp::Node
{
public:
  MyNode() : Node("node_name", "my_ns") {}
};

// 日志级别通过运行参数设置：--ros-args --log-level DEBUG
// 以下语句放在节点成员函数中。
RCLCPP_INFO_THROTTLE(get_logger(), *get_clock(), 1000,
  "此消息每秒最多输出一次");
RCLCPP_INFO_ONCE(get_logger(), "此消息只输出一次");

# 构建与运行
cd ~/my_robot_com260_ws
python3 -m colcon build --packages-select my_robot_pkg --symlink-install
source install/setup.bash
ros2 run my_robot_pkg my_node
 
# 查看节点
ros2 node list --no-daemon --spin-time 10                          # 列出所有节点
ros2 node info /my_first_node           # 查看节点详情
 
# 查看话题
ros2 topic list                         # 列出所有话题
ros2 topic echo /topic_name             # 监听话题消息
ros2 topic info /topic_name             # 查看话题信息
ros2 topic hz /topic_name               # 查看话题频率
 
# 查看包信息
ros2 pkg list                           # 列出所有包
ros2 pkg xml my_robot_pkg               # 查看包 XML

# 启动 rqt_graph 可视化节点通信图
rqt_graph
# 或通过 ros2 命令启动
ros2 run rqt_graph rqt_graph

# 启动 RViz2
rviz2
# 或指定配置文件
rviz2 -d /path/to/config.rviz

source /opt/ros/humble/setup.bash
source /workspace/install/setup.bash
 
# 终端 1：启动 Gazebo 仿真（无界面更省资源）
ros2 launch robot_sim_demo gazebo2.launch.py gui:=false rviz:=false drive:=false

source ~/.config/ros2-course-com260/env.bash
source ~/ros2_course_com260_ws/install/setup.bash
ros2 run demo_nodes_cpp listener

ros2 node list --no-daemon --spin-time 10          # 会看到 listener 以及其他仿真节点
ros2 node info /listener

source ~/.config/ros2-course-com260/env.bash
mkdir -p ~/my_scan_com260_ws/src
cd ~/my_scan_com260_ws/src
ros2 pkg create my_first_pkg --build-type ament_cmake \
  --dependencies rclcpp sensor_msgs

#include <memory>
#include "rclcpp/rclcpp.hpp"
#include "sensor_msgs/msg/laser_scan.hpp"
 
class ScanNode : public rclcpp::Node
{
public:
  ScanNode() : Node("my_node")
  {
    subscription_ = create_subscription<sensor_msgs::msg::LaserScan>(
      "/scan", rclcpp::SensorDataQoS(),
      [this](sensor_msgs::msg::LaserScan::ConstSharedPtr message) {
        RCLCPP_INFO_THROTTLE(get_logger(), *get_clock(), 1000,
          "SCAN_RECEIVED ranges=%zu frame=%s", message->ranges.size(),
          message->header.frame_id.c_str());
      });
  }
private:
  rclcpp::Subscription<sensor_msgs::msg::LaserScan>::SharedPtr subscription_;
};
 
int main(int argc, char ** argv)
{
  rclcpp::init(argc, argv);
  auto node = std::make_shared<ScanNode>();
  rclcpp::spin(node);
  node.reset();
  rclcpp::shutdown();
  return 0;
}

cmake_minimum_required(VERSION 3.10)
project(my_first_pkg)
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(sensor_msgs REQUIRED)
add_executable(my_node src/my_node.cpp)
target_compile_features(my_node PUBLIC cxx_std_17)
ament_target_dependencies(my_node rclcpp sensor_msgs)
install(TARGETS my_node DESTINATION lib/${PROJECT_NAME})
ament_package()

cd ~/my_scan_com260_ws
python3 -m colcon build --packages-select my_first_pkg --symlink-install
source install/setup.bash
ros2 run my_first_pkg my_node

ros2 node info /my_node
ros2 run my_first_pkg my_node --ros-args -r __node:=my_node2
# 在第三个同环境终端查询两个实例。
ros2 node list --no-daemon --spin-time 10