C语言使用mqtt协议向服务器发送心跳包

您可以使用MQTT C语言客户端库，如Eclipse Paho，来实现使用MQTT协议向服务器发送心跳包。以下是一个简单的示例代码：

#include "MQTTClient.h"

#define CLIENT_ID       "your_client_id"
#define SERVER_ADDRESS  "your_server_address"
#define SERVER_PORT     your_server_port
#define KEEP_ALIVE      60

int main(int argc, char* argv[])
{
    MQTTClient client;
    int rc;

    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    conn_opts.keepAliveInterval = KEEP_ALIVE;
    conn_opts.cleansession = 1;

    MQTTClient_create(&client, SERVER_ADDRESS, CLIENT_ID, MQTTCLIENT_PERSISTENCE_NONE, NULL);

    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS) {
        printf("Failed to connect, return code %d\n", rc);
        exit(EXIT_FAILURE);
    }

    while (1) {
        MQTTClient_publish(client, "your_topic", 0, "heartbeat", strlen("heartbeat"), 0, NULL);
        sleep(KEEP_ALIVE);
    }

    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);

    return rc;
}

您需要将`your_client_id`替换为您的客户端ID，`your_server_address`替换为您的服务器地址，`your_server_port`替换为您的服务器端口，`your_topic`替换为您的主题。

在代码中，发送心跳包的方法是使用`MQTTClient_publish`函数，将`"heartbeat"`作为消息内容发布到`"your_topic"`主题中。每隔`KEEP_ALIVE`秒，程序会发送一次心跳包。