使用 paho mqtt c实现MQTT发布

好的，这里提供一个简单的示例代码，使用 paho mqtt c 实现 MQTT 发布：

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

#define ADDRESS     "tcp://localhost:1883"
#define CLIENTID    "ExampleClientPub"
#define TOPIC       "test/topic"
#define QOS         1
#define TIMEOUT     10000L

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

    // 创建 MQTT 客户端
    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);
    }

    // 发布消息
    pubmsg.payload = "Hello, MQTT!";
    pubmsg.payloadlen = strlen(pubmsg.payload);
    pubmsg.qos = QOS;
    pubmsg.retained = 0;
    MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);
    printf("Waiting for publication of %s\n"
           "on topic %s for client with ClientID: %s\n",
           pubmsg.payload, TOPIC, CLIENTID);
    rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);
    printf("Message with delivery token %d delivered\n", token);

    // 断开连接并清理
    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);
    return rc;
}

这个示例代码实现了连接到本地的 MQTT 代理服务器，发布一条消息到 `test/topic` 主题，然后断开连接并清理。如果需要更改主题、代理服务器地址、客户端ID 等参数，请自行修改代码。