ROS2_04 - 8BitsCoding/RobotMentor GitHub Wiki

#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/int32.hpp"

rclcpp::Node::SharedPtr g_node = nullptr;

void topic_callback(const std_msgs::msg::Int32::SharedPtr msg)
{
  RCLCPP_INFO(g_node->get_logger(), "I heard: '%d'", msg->data);
}

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  g_node = rclcpp::Node::make_shared("simple_subscriber");
  auto subscription = g_node->create_subscription<std_msgs::msg::Int32>
      ("counter", topic_callback);
  rclcpp::spin(g_node);
  rclcpp::shutdown();
  
  subscription = nullptr;
  g_node = nullptr;
  return 0;
}

$ ros2 topic pub <topic_name> <message_type> <value>
# Example
$ ros2 topic pub /counter std_msgs/Int32 "{data: '5'}"

#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/int32.hpp"
using std::placeholders::_1;

class SimpleSubscriber : public rclcpp::Node
{
public:
  SimpleSubscriber()
  : Node("simple_subscriber")
  {
    subscription_ = this->create_subscription<std_msgs::msg::Int32>(
      "counter", std::bind(&SimpleSubscriber::topic_callback, this, _1));
  }

private:
  void topic_callback(const std_msgs::msg::Int32::SharedPtr msg)
  {
    RCLCPP_INFO(this->get_logger(), "I heard: '%d'", msg->data);
  }
  rclcpp::Subscription<std_msgs::msg::Int32>::SharedPtr subscription_;
};

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

$ cd ~/ros2_ws/src/<package_name>
$ mkdir msg

float32 years
float32 months
float32 days

find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)
find_package(builtin_interfaces REQUIRED)
find_package(rosidl_default_generators REQUIRED)

cmake_minimum_required(VERSION 3.5)
project(new_msg)

# Default to C99
if(NOT CMAKE_C_STANDARD)
  set(CMAKE_C_STANDARD 99)
endif()

# Default to C++14
if(NOT CMAKE_CXX_STANDARD)
  set(CMAKE_CXX_STANDARD 14)
endif()

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()

# find dependencies
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)
find_package(builtin_interfaces REQUIRED)
find_package(rosidl_default_generators REQUIRED)

if(BUILD_TESTING)
  find_package(ament_lint_auto REQUIRED)
  # the following line skips the linter which checks for copyrights
  # remove the line when a copyright and license is present in all source files
  set(ament_cmake_copyright_FOUND TRUE)
  # the following line skips cpplint (only works in a git repo)
  # remove the line when this package is a git repo
  set(ament_cmake_cpplint_FOUND TRUE)
  ament_lint_auto_find_test_dependencies()
endif()

rosidl_generate_interfaces(new_msg
  "msg/Age.msg"
  DEPENDENCIES builtin_interfaces
)

ament_package()

<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
  <name>new_msg</name>
  <version>0.0.0</version>
  <description>TODO: Package description</description>
  <maintainer email="[email protected]">ubuntu</maintainer>
  <license>TODO: License declaration</license>

  <buildtool_depend>ament_cmake</buildtool_depend>

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

  <build_depend>builtin_interfaces</build_depend>
  <build_depend>rosidl_default_generators</build_depend>
  <exec_depend>builtin_interfaces</exec_depend>
  <exec_depend>rosidl_default_runtime</exec_depend>

  <member_of_group>rosidl_interface_packages</member_of_group>

  <test_depend>ament_lint_auto</test_depend>
  <test_depend>ament_lint_common</test_depend>

  <export>
    <build_type>ament_cmake</build_type>
  </export>
</package>