ROS 2 C++ Publisher | ROS 2 | Tech Arcanist

NOTE: I will be prioritizing Python and temporarily pausing C++ implementations after Chapter 36. You can go through the C++ chapters covered up to Chapter 36. After that, I will complete the remaining topics in Python first, then revisit the skipped chapters to add their C++ implementations.

Open Visual Studio Code

What you do

Open Visual Studio Code
Click Open Folder

Now

Select: bumperbot_ws
Click Yes, I trust the authors

Navigate to the C++ Package

Inside VS Code, go step by step:

src
└── bumperbot_cpp_examples
└── src

Create the C++ Node File

What you do

Right-click on src
Click New File
Name it:

simple_publisher.cpp

This file will contain our ROS 2 node code.

C++ Node Implementation

#include <rclcpp/rclcpp.hpp>
#include <std_msgs/msg/string.hpp>
#include <chrono>

using namespace std::chrono_literals;

class SimplePublisher : public rclcpp::Node
{
public:
  SimplePublisher() : Node("simple_publisher"), counter_(0)
  {
    pub_ = create_publisher<std_msgs::msg::String>("chatter", 10);
    timer_ = create_wall_timer(1s, std::bind(&SimplePublisher::timerCallback, this));
    RCLCPP_INFO(get_logger(), "Publishing at 1 Hz");
  }

  void timerCallback()
  {
    auto message = std_msgs::msg::String();
    message.data = "Hello ROS 2 - counter:" + std::to_string(counter_++);
    pub_->publish(message);
  }

private:
  rclcpp::Publisher<std_msgs::msg::String>::SharedPtr pub_;
  rclcpp::TimerBase::SharedPtr timer_;
  unsigned int counter_;
};

int main(int argc, char* argv[])
{
  rclcpp::init(argc, argv);
  auto node = std::make_shared<SimplePublisher>();
  rclcpp::spin(node);
  rclcpp::shutdown();
  return 0;
}

simplepublisher.cpp code

CMakeLists.txt

Open: CMakeLists.txt

find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)

add_executable(simple_publisher src/simple_publisher.cpp)
ament_target_dependencies(simple_publisher rclcpp std_msgs)

install(TARGETS
  simple_publisher
  DESTINATION lib/${PROJECT_NAME}
)

Explanation

Short version

find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)

These find the ROS 2 packages/dependencies your code needs.

add_executable(simple_publisher src/simple_publisher.cpp)

Means:

simple_publisher → your executable/target name
src/simple_publisher.cpp → your C++ source file

You can change simple_publisher to anything:

add_executable(my_publisher src/simple_publisher.cpp)

But then change it everywhere else too:

ament_target_dependencies(my_publisher rclcpp std_msgs)

install(TARGETS
  my_publisher
  DESTINATION lib/${PROJECT_NAME}
)

Finally:

${PROJECT_NAME}

is a CMake variable containing the name from:

project(bumperbot_cpp_examples)

So ${PROJECT_NAME} = bumperbot_cpp_examples.

Remember:

rclcpp / std_msgs       → ROS 2 dependencies
simple_publisher        → YOUR executable name
simple_publisher.cpp    → YOUR source file
${PROJECT_NAME}         → CMake variable

package.xml

Open: bumperbot_py_examples/package.xml

  <depend>rclcpp</depend>
  <depend>std_msgs</depend>

Explanation

Word	Meaning
`install`	Copies compiled file to install folder
`TARGETS`	Which executable to install
`DESTINATION`	Where to place it
`lib/${PROJECT_NAME}`	Standard ROS 2 install path

Build the Workspace

cd bumperbot_ws/

colcon build

Converts cpp script into ROS 2 executable

Activate the Workspace

. install/setup.bash

ros2 run bumperbot_cpp_examples simple_publisher

Inspect Topics

ros2 topic list

Shows all active topics in the ROS 2 system
Topics appear only if some node is using them

ros2 topic echo /chatter

/chatter → your publisher is running
If /chatter is NOT listed → publisher is not active

Use this when

You want to check which topics exist
You want to verify your node is publishing