ros2编写一个三个数相乘的服务

在ROS 2中，你可以创建一个服务（service），让用户请求并得到三个数相乘的结果。首先，你需要定义一个服务接口（service interface），通常是一个消息类型（message type）用于描述输入参数和返回值。然后，你可以编写服务器端（server）处理来自客户端的请求，并在客户端编写客户端代码来调用这个服务。

以下是简单的步骤：

1. 定义服务接口（例如名为`multiply_three_numbers`）：

// multiply_service_msgs/msg/MultiplyThreeNumbers.h
#include <ros2/service_traits.hpp>
namespace multiply_service {
struct MultiplyThreeNumbers_Request {
    int32_t num1;
    int32_t num2;
    int32_t num3;
};
typedef std::shared_ptr<MultiplyThreeNumbers_Request> MultiplyThreeNumbers_RequestSharedPtr;
struct MultiplyThreeNumbers_Response {
    int64_t result;
};
typedef std::shared_ptr<MultiplyThreeNumbers_Response> MultiplyThreeNumbers_ResponseSharedPtr;
}  // namespace multiply_service

2. 编写服务实现（server）：

// server.cpp
#include "multiply_service_msgs/srv/multiply_three_numbers.hpp"
#include "rclcpp/rclcpp.hpp"

class MultiplyService : public rclcpp::Node
{
public:
  explicit MultiplyService(rclcpp::NodeOptions options)
      : Node("multiply_service", options),
        server_(this->create_service<multiply_service::MultiplyThreeNumbersRequest, multiply_service::MultiplyThreeNumbersResponse>(
          "multiply_three_numbers",
          [this](auto request) -> rclcpp::executor::Future<multiply_service::MultiplyThreeNumbersResponse> {
            RCLCPP_INFO(get_logger(), "Received multiply request: %d, %d, %d", request.num1, request.num2, request.num3);
            auto response = multiply_service::MultiplyThreeNumbersResponse();
            response.result = request.num1 * request.num2 * request.num3;
            return rclcpp::make_future(response);
          }))
  {}

private:
  rclcpp::Server<multiply_service::MultiplyThreeNumbersRequest, multiply_service::MultiplyThreeNumbersResponse>::SharedPtr server_;
};

3. 启动服务：

int main(int argc, char ** argv)
{
  rclcpp::init(argc, argv);
  auto node = rclcpp::Node::make_shared<MultiplyService>(rclcpp::NodeOptions());
  rclcpp::spin(node);
  rclcpp::shutdown();
  return 0;
}

4. 客户端调用服务：

// client.cpp
#include "multiply_service_msgs/srv/multiply_three_numbers.hpp"

void call_multiply_service()
{
  rclcpp::Client<multiply_service::MultiplyThreeNumbersResponse> client("multiply_three_numbers");
  if (!client.wait_for_service(std::chrono::seconds(5))) {
    RCLCPP_ERROR(client.get_logger(), "Failed to connect to multiply service.");
    return;
  }

  auto request = multiply_service::MultiplyThreeNumbersRequest();
  request.num1 = 2;
  request.num2 = 3;
  request.num3 = 4;

  auto future = client.call_async(request);

  if (future.wait_for_result(std::chrono::seconds(5)) == rclcpp::executor::Result::SUCCESS) {
    const auto& response = future.get_result();
    RCLCPP_INFO(client.get_logger(), "Product of numbers is: %ld", response.result);
  } else {
    RCLCPP_ERROR(client.get_logger(), "Failed to get the multiplication result.");
  }
}

int main(int argc, char ** argv)
{
  rclcpp::init(argc, argv);
  call_multiply_service();
  rclcpp::shutdown();
  return 0;
}