提供一个简单的用c语言的Eclipse Paho MQTT的客户端代码

好的，以下是一个简单的 C 代码片段，用于连接到 MQTT 代理并发布消息，需要使用 Eclipse Paho MQTT C 客户端库：

#include "MQTTClient.h"

#define ADDRESS     "tcp://mqtt.eclipse.org:1883"
#define CLIENTID    "c-sample"
#define TOPIC       "test/topic"
#define PAYLOAD     "Hello, World!"
#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;

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

    MQTTClient_connect(client, &conn_opts);
    pubmsg.payload = (void*)PAYLOAD;
    pubmsg.payloadlen = (int)strlen(PAYLOAD);
    pubmsg.qos = QOS;
    pubmsg.retained = 0;

    MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);
    rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);
    printf("Message delivered %d\n", rc);

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

这个客户端连接到 Eclipse 的公共 MQTT 测试代理，并发布一条消息到 "test/topic" 主题。你可以根据你的实际需求进行修改。注意，需要在代码中引用 Paho MQTT C 客户端库头文件并链接该库。