用c++语言编写代码，要求如下：用ros2编写一个温度服务节点，该节点提供一个名为“tem”的服务，该服务节点使用模拟数据生成一个随机的浮点数作为温度值，并返回给客户端。再编写一个温度客户端节点，连接到温度服务节点并发送请求，接收到温度值后，打印到控制台。

以下是实现该要求的代码：

**温度服务节点**

#include "rclcpp/rclcpp.hpp"
#include "example_interfaces/srv/get_float.hpp"
#include <cstdlib>
#include <ctime>

using std::placeholders::_1;
using std::placeholders::_2;

class TemperatureServer : public rclcpp::Node
{
public:
  TemperatureServer()
  : Node("temperature_server")
  {
    // 创建服务
    temperature_service_ = this->create_service<example_interfaces::srv::GetFloat>("tem",
        std::bind(&TemperatureServer::handle_temperature_service_request, this, _1, _2));
  }

private:
  void handle_temperature_service_request(const std::shared_ptr<example_interfaces::srv::GetFloat::Request> request,
      std::shared_ptr<example_interfaces::srv::GetFloat::Response> response)
  {
    // 生成模拟温度数据
    srand((unsigned)time(NULL));
    float temperature = (float)(rand() % 100) + ((float)(rand() % 100)) / 100;

    // 返回温度数据
    response->temperature = temperature;
    RCLCPP_INFO(this->get_logger(), "Temperature service: Temperature value returned: %.2f", temperature);
  }

  rclcpp::Service<example_interfaces::srv::GetFloat>::SharedPtr temperature_service_;
};

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

**温度客户端节点**

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

using std::placeholders::_1;
using std::placeholders::_2;

class TemperatureClient : public rclcpp::Node
{
public:
  TemperatureClient()
  : Node("temperature_client")
  {
    // 创建客户端
    temperature_client_ = this->create_client<example_interfaces::srv::GetFloat>("tem");
  }

  void request_temperature()
  {
    while (!temperature_client_->wait_for_service(std::chrono::seconds(1))) {
      if (!rclcpp::ok()) {
        RCLCPP_ERROR(this->get_logger(), "Interrupted while waiting for the service. Exiting.");
        return;
      }
      RCLCPP_INFO(this->get_logger(), "Waiting for the service to become available...");
    }

    // 发送请求
    auto request = std::make_shared<example_interfaces::srv::GetFloat::Request>();
    auto future_result = temperature_client_->async_send_request(request);

    // 接收响应
    if (rclcpp::spin_until_future_complete(this->get_node_base_interface(), future_result) !=
        rclcpp::executor::FutureReturnCode::SUCCESS)
    {
      RCLCPP_ERROR(this->get_logger(), "Failed to receive temperature value.");
      return;
    }

    auto response = future_result.get();
    RCLCPP_INFO(this->get_logger(), "Temperature client: Temperature value received: %.2f", response->temperature);
  }

private:
  rclcpp::Client<example_interfaces::srv::GetFloat>::SharedPtr temperature_client_;
};

int main(int argc, char **argv)
{
  rclcpp::init(argc, argv);
  auto temperature_client = std::make_shared<TemperatureClient>();
  temperature_client->request_temperature();
  rclcpp::shutdown();
  return 0;
}

使用方法：

1. 编译

$ colcon build

2. 运行服务节点

$ ros2 run temperature_service temperature_server

3. 运行客户端节点

$ ros2 run temperature_client temperature_client

客户端节点将会向服务节点发送请求，接收到响应后打印温度值到控制台。服务节点将会在接收到请求后生成一个随机的浮点数作为温度值，并返回给客户端。