mqtt客户端c代码

MQTT客户端C代码是一种基于C语言编写的用于实现MQTT（Message Queuing Telemetry Transport，消息队列遥测传输）协议的客户端程序。以下是一段简单的MQTT客户端C代码示例：

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

#define ADDRESS "tcp://localhost:1883"
#define CLIENTID "ExampleClient"
#define TOPIC "exampleTopic"
#define QOS 1
#define TIMEOUT 10000L

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

    MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_DEFAULT, NULL);
    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;

    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");

    if ((rc = MQTTClient_subscribe(client, TOPIC, QOS)) != MQTTCLIENT_SUCCESS) {
        printf("Failed to subscribe, return code %d\n", rc);
        exit(EXIT_FAILURE);
    }
    printf("Subscribed to topic: %s\n", TOPIC);

    while (1) {
        MQTTClient_receive(client, &received_message, TIMEOUT);
        if (received_message) {
            printf("Received message: %s\n", received_message->payload);
            MQTTClient_freeMessage(&received_message);
            MQTTClient_yield();
        }
    }

    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);
    return EXIT_SUCCESS;
}

上述代码创建了一个MQTT客户端，并连接到指定的MQTT代理服务器。它订阅了一个名为"exampleTopic"的主题，并在收到消息时打印出消息内容。该客户端将持续监听服务器发送的消息，直到程序手动终止。