Linux Mqtt客户端编程

安装Eclipse Paho MQTT C++库

1. 安装依赖项：

   sudo apt-get update sudo apt-get install libpaho-mqttpp-dev libpaho-mqtt-dev

2. 下载和编译Eclipse Paho MQTT C++库：

   git clone https://github.com/eclipse/paho.mqtt.cpp.git 
   cd paho.mqtt.cpp 
   mkdir build 
   cd build 
   cmake .. 
   make 
   sudo make install

编写MQTT客户端程序

#include 
#include 
#include 
#include 
#include "mqtt/async_client.h"

// 定义MQTT服务器地址和客户端ID
const std::string SERVER_ADDRESS("tcp://mqtt.eclipse.org:1883");
const std::string CLIENT_ID("paho_cpp_async_publish_subscribe");

const std::string TOPIC("test_topic");
const int QOS = 1;
const auto TIMEOUT = std::chrono::seconds(10);

class callback : public virtual mqtt::callback,
                 public virtual mqtt::iaction_listener
{
    // 消息到达时的回调函数
    void message_arrived(mqtt::const_message_ptr msg) override {
        std::cout << "Message arrived" << std::endl;
        std::cout << "    topic: '" << msg->get_topic() << "'" << std::endl;
        std::cout << "    payload: '" << msg->to_string() << "'" << std::endl;
    }

    // 连接丢失时的回调函数
    void connection_lost(const std::string& cause) override {
        std::cout << "\nConnection lost" << std::endl;
        if (!cause.empty())
            std::cout << "Cause: " << cause << std::endl;
    }

    // 订阅成功或失败时的回调函数
    void on_failure(const mqtt::token& tok) override {
        std::cout << "Subscription failed" << std::endl;
    }

    void on_success(const mqtt::token& tok) override {
        std::cout << "Subscription succeeded" << std::endl;
    }
};

int main(int argc, char* argv[]) {
    // 创建MQTT异步客户端
    mqtt::async_client client(SERVER_ADDRESS, CLIENT_ID);

    // 设置回调函数
    callback cb;
    client.set_callback(cb);

    // 设置连接选项
    mqtt::connect_options connOpts;
    connOpts.set_clean_session(true);

    try {
        // 连接到MQTT服务器
        std::cout << "Connecting to the MQTT server..." << std::flush;
        mqtt::token_ptr conntok = client.connect(connOpts);
        conntok->wait();
        std::cout << "OK" << std::endl;

        // 订阅主题
        std::cout << "Subscribing to topic '" << TOPIC << "'..." << std::flush;
        client.subscribe(TOPIC, QOS, nullptr, cb);
        std::cout << "OK" << std::endl;

        // 发布消息
        std::string payload = "Hello, MQTT!";
        mqtt::message_ptr pubmsg = mqtt::make_message(TOPIC, payload);
        pubmsg->set_qos(QOS);
        client.publish(pubmsg)->wait_for(TIMEOUT);
        std::cout << "Message published" << std::endl;

        // 等待一段时间，以接收消息
        std::this_thread::sleep_for(std::chrono::seconds(10));

        // 断开连接
        std::cout << "Disconnecting from the MQTT server..." << std::flush;
        conntok = client.disconnect();
        conntok->wait();
        std::cout << "OK" << std::endl;
    }
    catch (const mqtt::exception& exc) {
        std::cerr << exc.what() << std::endl;
        return 1;
    }

    return 0;
}

编译和运行程序

1. 创建CMakeLists.txt：

   cmake_minimum_required(VERSION 3.5)
   project(MQTTClient)
   
   set(CMAKE_CXX_STANDARD 11)
   
   find_package(PahoMqttCpp REQUIRED)
   
   add_executable(MQTTClient main.cpp)
   target_link_libraries(MQTTClient PahoMqttCpp::paho-mqttpp3)