mosquitto使用mqtt中一个奇怪的现象

    初次使用mqtt，然后就去找了一个库libmosquitto.so.1，然后就看了下头文件mosquitto.h，找了一下例子。然后就跑起来了

 /* libmosquitto lib init */
    mosquitto_lib_init();
    /* create a mosquitto client */
    mosq = mosquitto_new(device_id, false, mqqtcdev);
    if(!mosq)
    {
        printf("create client failed..\n");
        mosquitto_lib_cleanup();
        return -1;
    }
    
    /* set the username and password */
    mosquitto_username_pw_set(mosq, username, password);

    /* set log call callback */
   // mosquitto_log_callback_set(mosq, my_log_callback);

    /* set connect callback */
    mosquitto_connect_callback_set(mosq, my_connect_callback);

    /* set message callback */
    mosquitto_message_callback_set(mosq, my_message_callback);

    /* set subscribe callback */
    mosquitto_subscribe_callback_set(mosq, my_subscribe_callback);

    /* connect to the broker */
    if(mosquitto_connect(mosq, MQTT_SERVER_ADDR, MQTT_SERVER_PORT, MQQT_KEEPALIVE))
    {
        fprintf(stderr, "Unable to connect.\n");
        return -1;
    }
    
    /* 循环处理网络消息 */
    mosquitto_loop_forever(mosq, -1, 1);

    mosquitto_destroy(mosq);
    mosquitto_lib_cleanup();
    return 0;

 

 

static void my_connect_callback(struct mosquitto *mosq, void *userdata, int result)
{

    ret = mosquitto_subscribe(mosq,  NULL, "12345/67800/sub", 2);

}

 

static void my_subscribe_callback(struct mosquitto *mosq, void *userdata, int mid, int qos_count, const int *granted_qos)
{

    printf("Subscribed (mid: %d): %d\n", mid, granted_qos[0]);
    printf("Subscribed qos_count: %d\n", qos_count);

}

static void my_message_callback(struct mosquitto *mosq, void *userdata, const struct mosquitto_message *message)
{
    int ret = 0;
    printf("mqtt have a message, msglen=%d\n", message->payloadlen);

}

这个吊样mqtt就使用起来了，开始还能正常工作，但是用着用着就订阅不了了，不知道什么原因。后来给订阅的函数加了个mid就好了，也不知道怎么回四，也没时间看，记录一下。看有没有有志青年去探究一下。

  int mid = 0;

    ret = mosquitto_subscribe(mosq,  &mid, "12345/67800/sub", 2);