c++基于mosqpp实现mqtt客户端 完整示例代码

在C++中使用MqttClient库（如Mosquitto C++客户端库mosquittopp）来实现MQTT客户端是一个常见的任务。以下是创建一个基本的MQTT客户端连接、订阅主题并接收消息的简单示例。请注意，这个例子假设您已经安装了mosquittopp库，并且已经在项目中包含了相应的头文件。

#include <mosquitto.h>
#include <iostream>

class MqttClient {
public:
    MqttClient(const std::string& broker_address, const std::string& client_id) : 
        mqtt_(mosquitto_new(client_id.c_str(), true, nullptr)) {}

    void connect() {
        if (mqtt_) {
            mosquitto_connect(mqtt_, broker_address.c_str(), 1883, 60);
            while (!mosquitto_connack_rdy(mqtt_)); // 等待连接完成
            std::cout << "Connected to MQTT broker." << std::endl;
        }
    }

    void subscribe(const std::string& topic) {
        int result = mosquitto.subscribe(mqtt_, topic.c_str(), 1); // QoS 1 for at least once delivery
        if (result == MOSQ_ERR_SUCCESS) {
            std::cout << "Subscribed to topic: " << topic << std::endl;
        } else {
            std::cerr << "Failed to subscribe: " << mosquitto_error_string(result) << std::endl;
        }
    }

    void on_message(const struct mosquitto_message* message) {
        std::cout << "Received message on topic: " << message->topic << ", payload: " << std::string((char*)message->payload, message->payload_len) << std::endl;
    }

private:
    mosquitto* mqtt_;
};

int main() {
    MqttClient client("localhost", "client-1");
    client.connect();
    client.subscribe("test/topic");

    // 模拟消息接收，通常由 Mosquitto 库自动处理回调
    mosquitto_loop_forever(mqtt_, -1);

    // 关闭连接前，记得清理资源
    mosquitto_destroy(mqtt_);
    return 0;
}