ROS 2 Messages¶

Message Types¶

ROS 2 messages are strongly-typed structures defined in .msg files. Examples:

std_msgs/msg/String
geometry_msgs/msg/Twist
sensor_msgs/msg/LaserScan

Standard Message Packages¶

Common message packages you will encounter include:

std_msgs – basic types such as strings, integers, and booleans.
geometry_msgs – vectors, poses, twists, etc.
sensor_msgs – common sensor data types.
nav_msgs – navigation-related messages such as OccupancyGrid.

Message Introspection¶

Use the ROS 2 CLI to inspect messages and topics:

List topics:
```
ros2 topic list
```
Show the type of a topic:
```
ros2 topic info /cmd_vel
```

Inspect a message definition:

ros2 interface show geometry_msgs/msg/Twist

Using Messages in C++¶

Example: publishing a geometry_msgs/msg/Twist:

#include "geometry_msgs/msg/twist.hpp"

geometry_msgs::msg::Twist cmd;
cmd.linear.x  = 0.5;
cmd.angular.z = 0.0;

publisher_->publish(cmd);

Remember to:

Include the appropriate message header.
Add the package to ament_target_dependencies in CMakeLists.txt.