Paho MQTT C库多话题订阅代码

好的，以下是使用 Paho MQTT C 库实现多话题订阅的代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <MQTTClient.h>

#define ADDRESS     "tcp://mqtt.example.com:1883"
#define CLIENTID    "ExampleClientSub"
#define QOS         1
#define TIMEOUT     10000L

int main(int argc, char* argv[])
{
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    MQTTClient_message* msg = NULL;
    MQTTClient_deliveryToken token;
    int rc;

    // 创建 MQTT 客户端实例
    MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);

    // 设置连接选项
    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;

    // 连接到 MQTT 代理服务器
    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS) {
        printf("Failed to connect, return code %d\n", rc);
        exit(EXIT_FAILURE);
    }
    printf("Connected to MQTT broker\n");

    // 订阅多个主题
    const char* topics[] = {"test/topic1", "test/topic2", "test/topic3"};
    int qos[] = {QOS, QOS, QOS};
    int count = sizeof(topics) / sizeof(char*);
    MQTTClient_subscribeMany(client, count, topics, qos);

    // 循环接收消息
    while (1) {
        MQTTClient_messageArrived(client, NULL, msg);
        printf("Received message on topic: %s, payload: %.*s\n", msg->topicName->lenstring.data, (int)msg->payloadlen, (char*)msg->payload);
        MQTTClient_freeMessage(&msg);
        MQTTClient_free(topicName);
    }

    // 断开连接
    MQTTClient_disconnect(client, TIMEOUT);
    MQTTClient_destroy(&client);

    return rc;
}

在以上代码中，首先创建了一个 MQTT 客户端实例，并设置连接选项。然后连接到 MQTT 代理服务器，如果连接失败则打印错误信息并退出程序。

接着使用 `MQTTClient_subscribeMany()` 方法订阅多个主题，其中 `topics` 数组存储了多个主题名称，`qos` 数组存储了对应主题的 QoS 等级。

最后使用循环不断接收消息，并打印输出消息的主题和负载内容，直到程序被手动终止为止。

希望这个示例能够帮助到你。