roscpp publish int32 - C++

Introduction

In this tutorial, we will learn how to publish an integer message using ROS C++ API (roscpp). We will use roscpp to create a publisher node that sends integer messages to a topic.

Prerequisites

• ROS (Robot Operating System) installed on your system.
• Basic understanding of ROS concepts, such as topics, messages, nodes, and publishers/subscribers.

Create a ROS package

We will start by creating a new ROS package called demo_package. Open a terminal window and execute the following command:

$ cd ~/catkin_ws/src
$ catkin_create_pkg demo_package roscpp std_msgs

This command will create a new ROS package with the dependencies roscpp and std_msgs.

Building the package

Execute the following commands in your terminal to build the package:

$ cd ~/catkin_ws
$ catkin_make

Writing the publisher node

1. Create a new source file publisher_node.cpp inside the src directory of your package.

2. Include the necessary headers:

#include <ros/ros.h>
#include <std_msgs/Int32.h>

3. Add the main function and create a node handle:

int main(int argc, char **argv)
{
    // Initialize the ROS node
    ros::init(argc, argv, "publisher_node");
    ros::NodeHandle nh;

    // ...
}

4. Create a publisher object that publishes integer messages:

ros::Publisher pub = nh.advertise<std_msgs::Int32>("int_topic", 10);

This creates a publisher object pub that publishes integer messages to the topic int_topic.

5. Create a loop that publishes the messages:

ros::Rate loop_rate(1); // loop at 1 Hz

while (ros::ok()) { // run until the node is terminated
    std_msgs::Int32 msg;
    msg.data = 42;

    pub.publish(msg); // publish the message

    ros::spinOnce();
    loop_rate.sleep();
}

This loop publishes integer messages with the value 42 at a rate of 1 Hz.

6. Full code for the publisher node:

#include <ros/ros.h>
#include <std_msgs/Int32.h>

int main(int argc, char **argv)
{
    // Initialize the ROS node
    ros::init(argc, argv, "publisher_node");
    ros::NodeHandle nh;

    // Create a publisher that sends integer messages to "int_topic" topic
    ros::Publisher pub = nh.advertise<std_msgs::Int32>("int_topic", 10);

    // Loop at 1 Hz and publish integer messages with value 42
    ros::Rate loop_rate(1);

    while (ros::ok()) {
        std_msgs::Int32 msg;
        msg.data = 42;

        pub.publish(msg);

        ros::spinOnce();
        loop_rate.sleep();
    }

    return 0;
}

Running the node

Execute the following command in your terminal to run the node:

$ rosrun demo_package publisher_node

This should start the publisher node and publish integer messages to the topic int_topic.

Conclusion

In this tutorial, we learned how to create a simple ROS publisher node that sends integer messages using roscpp. We created a ROS package and wrote a simple publisher node that publishes messages to a topic. We also ran the node and confirmed that it correctly published messages to the topic.