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How to write header file for ROS 2 publisher [closed]

asked 2021-06-11 04:23:38 -0500

cjoshi17 gravatar image


I am relatively new to ROS 2. I have worked on ROS and can make header files for my class. I am trying to replicate the same thing for ROS 2. I am following the Pub Sub tutorial on ROS 2 documentation. However, in that they have defined the class and the main function inside one .cpp file. I want to define the class in a .h file, make a corresponding .cpp file of the class and call the entire thing in a main.cpp file

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Closed for the following reason the question is answered, right answer was accepted by cjoshi17
close date 2022-07-14 01:48:43.034315

1 Answer

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answered 2021-06-11 21:10:54 -0500

404RobotNotFound gravatar image

updated 2021-06-11 21:12:34 -0500

It can be done, you just need to build the files correctly. Taking the minimum publisher as an example, you can break it up into different files:


#include <chrono>
#include <functional>
#include <memory>
#include <string>

#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"

class MinimalPublisher : public rclcpp::Node

  void timer_callback();
  rclcpp::TimerBase::SharedPtr timer_;
  rclcpp::Publisher<std_msgs::msg::String>::SharedPtr publisher_;
  size_t count_;


#include "minimal_publisher.hpp"

MinimalPublisher::MinimalPublisher ()
: Node("minimal_publisher"), count_(0)
    publisher_ = this->create_publisher<std_msgs::msg::String>("topic", 10);
    timer_ = this->create_wall_timer(
      500ms, std::bind(&MinimalPublisher::timer_callback, this));

    auto message = std_msgs::msg::String(); = "Hello, world! " + std::to_string(count_++);
    RCLCPP_INFO(this->get_logger(), "Publishing: '%s'",;


#include "minimal_publisher.hpp"

int main(int argc, char * argv[])
  rclcpp::init(argc, argv);
  return 0;

Now you just need to be able to build it correctly. If you don't care exactly, you can wrap it all into one add_executable call in the CMakeLists.txt. Or, you can build them minimal_publisher.hpp and .cpp as a library and then the minimal_publisher_node.cpp as an executable and link the library.

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Thanks for solving my problem. I had defined my .h and corresponding .cpp file like you have mentioned in the answer. The step I was doing wrong was in the CMakeLists.txt. I defined an executable for my publisher.cpp, subscriber.cpp and main.cpp instead of having it all defined in one executable like this

Wrong way:

add_executable(talker src/publisher.cpp) ament_target_dependencies(talker rclcpp std_msgs)

add_executable(listener src/subscriber.cpp) ament_target_dependencies(listener rclcpp std_msgs)

add_executable(main_node src/main.cpp) ament_target_dependencies(main_node rclcpp std_msgs)

Correct way:

add_executable(main_node src/main.cpp src/publisher.cpp src/subscriber.cpp) ament_target_dependencies(main_node rclcpp std_msgs)

Thanks again for solving my problem. I have been coding in python for a few months now and hence forgotten about the whole CMake definitions for C++.

cjoshi17 gravatar image cjoshi17  ( 2021-06-11 23:56:53 -0500 )edit

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Asked: 2021-06-11 04:23:38 -0500

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Last updated: Jun 11 '21