ROS2与C++入门教程-编写服务端和客户端

ROS2与C++入门教程-编写服务端和客户端

说明：

• 介绍如何编写服务端和客户端

编写服务端步骤：

• 新建包cpp_srvcli

cd ~/dev_ws/src
ros2 pkg create --build-type ament_cmake cpp_srvcli --dependencies rclcpp example_interfaces

• 依赖example_interfaces包，将会使用到example_interfaces的srv文件
• 进入srv目录，新建文件add_two_ints_server.cpp

vim add_two_ints_server.cpp

• 内容如下：

#include "rclcpp/rclcpp.hpp"
#include "example_interfaces/srv/add_two_ints.hpp"

#include <memory>

void add(const std::shared_ptr<example_interfaces::srv::AddTwoInts::Request> request,
          std::shared_ptr<example_interfaces::srv::AddTwoInts::Response>      response)
{
  response->sum = request->a + request->b;
  RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "Incoming request\na: %ld" " b: %ld",
                request->a, request->b);
  RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "sending back response: [%ld]", (long int)response->sum);
}

int main(int argc, char **argv)
{
  rclcpp::init(argc, argv);

  std::shared_ptr<rclcpp::Node> node = rclcpp::Node::make_shared("add_two_ints_server");

  rclcpp::Service<example_interfaces::srv::AddTwoInts>::SharedPtr service =
    node->create_service<example_interfaces::srv::AddTwoInts>("add_two_ints", &add);

  RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "Ready to add two ints.");

  rclcpp::spin(node);
  rclcpp::shutdown();
}

• 修改CMakeLists.txt，增加如下行：

add_executable(server src/add_two_ints_server.cpp)
ament_target_dependencies(server
rclcpp example_interfaces)

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

编写客户端步骤：

• 进入srv目录，新建文件add_two_ints_client.cpp
• 如下内容：

#include "rclcpp/rclcpp.hpp"
#include "example_interfaces/srv/add_two_ints.hpp"

#include <chrono>
#include <cstdlib>
#include <memory>

using namespace std::chrono_literals;

int main(int argc, char **argv)
{
  rclcpp::init(argc, argv);

  if (argc != 3) {
      RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "usage: add_two_ints_client X Y");
      return 1;
  }

  std::shared_ptr<rclcpp::Node> node = rclcpp::Node::make_shared("add_two_ints_client");
  rclcpp::Client<example_interfaces::srv::AddTwoInts>::SharedPtr client =
    node->create_client<example_interfaces::srv::AddTwoInts>("add_two_ints");

  auto request = std::make_shared<example_interfaces::srv::AddTwoInts::Request>();
  request->a = atoll(argv[1]);
  request->b = atoll(argv[2]);

  while (!client->wait_for_service(1s)) {
    if (!rclcpp::ok()) {
      RCLCPP_ERROR(rclcpp::get_logger("rclcpp"), "Interrupted while waiting for the service. Exiting.");
      return 0;
    }
    RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "service not available, waiting again...");
  }

  auto result = client->async_send_request(request);
  // Wait for the result.
  if (rclcpp::spin_until_future_complete(node, result) ==
    rclcpp::FutureReturnCode::SUCCESS)
  {
    RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "Sum: %ld", result.get()->sum);
  } else {
    RCLCPP_ERROR(rclcpp::get_logger("rclcpp"), "Failed to call service add_two_ints");
  }

  rclcpp::shutdown();
  return 0;
}

• 编辑CMakeLists.txt，内容如下：

cmake_minimum_required(VERSION 3.5)
project(cpp_srvcli)

find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(example_interfaces REQUIRED)

add_executable(server src/add_two_ints_server.cpp)
ament_target_dependencies(server
  rclcpp example_interfaces)

add_executable(client src/add_two_ints_client.cpp)
ament_target_dependencies(client
  rclcpp example_interfaces)

install(TARGETS
  server
  client
  DESTINATION lib/${PROJECT_NAME})

ament_package()

编译包：

• 安装依赖包

rosdep install -i --from-path src --rosdistro <distro> -y

• 编译

colcon build --packages-select cpp_srvcli

测试：

• 新开终端，启动服务端

cd ~/dev_ws/
. install/setup.bash
ros2 run cpp_srvcli server

• 效果如下：

[INFO] [rclcpp]: Ready to add two ints.
[INFO] [rclcpp]: Incoming request
a: 2 b: 3
[INFO] [rclcpp]: sending back response: [5]

• 新开终端，启动客户端

cd ~/dev_ws/
. install/setup.bash
ros2 run cpp_srvcli client 2 3

• 效果如下：

[INFO] [rclcpp]: Sum: 5