Mosquitto发布者不在C中发布整数

Question

我正在使用Paho客户端库来编写一个客户端，该客户端向mosquitto代理发布一个整数。当我将有效负载设置为字符串时，它会毫无问题地发布，但是当我将有效负载设置为整数时，发布者会崩溃并显示以下消息，如图所示。

我的客户端代码如下：

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

#define ADDRESS     "tcp://localhost:1883"
#define CLIENTID    "ExampleClientPub"
#define TOPIC       "MQTT Examples"
#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, ch;
   int i = 4;

   MQTTClient_create(&client, ADDRESS, CLIENTID,
   MQTTCLIENT_PERSISTENCE_NONE, NULL);
   conn_opts.username = "user";
   conn_opts.password = "hello";
   conn_opts.keepAliveInterval = 65000;
   conn_opts.cleansession = 1;

   if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
  {
    printf("Failed to connect, return code %d\n", rc);
    exit(-1);
  }
   pubmsg.payload = i;
   pubmsg.payloadlen = sizeof(i);  //strlen(PAYLOAD);
   pubmsg.qos = QOS;
   pubmsg.retained = 0;
   MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);
   printf("Waiting for up to %d seconds for publication of %d\n"
    "on topic %s for client with ClientID: %s\n",
    (int)(TIMEOUT / 1000), i, TOPIC, CLIENTID);
   rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);
   printf("Message with delivery token %d delivered\n", token);
  do
  {
    ch = getchar();
  } while (ch != 'Q' && ch != 'q');
    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);
    return rc;
}

有谁能告诉我我做错了什么？

Answer 1

payload的类型为char *

typedef struct {
    char * topic;
    char * payload;
    unsigned int length;
    boolean retained;
} MQTTMessage;

这意味着它只接受字符串。

Answer 2

如果有人遇到这篇文章，这对我有用：

发布为：

  uint32_t mmsg = (2<<31)-1;
  mosquitto_publish(mosq, NULL, "topic\0", 4, &mmsg, 2, false);

读为

  LOGD("Message topic and load are %s and %lu\n ", msg->topic, *((uint32_t *) (msg->payload)));

LOGD只是fprintf（stdout，....）

周围的一个宏

Answer 3

Select tf4hid,tf4iid,date,product,planqty from tf4i group by date,product 的{​​{1}}字段是payload，如果要发送整数，则需要使用一个指针并将其正确地强制转换：

MQTTClient_message