//打开网络连接
mysock = transport\_open(host, port);
if(mysock < 0)
return mysock;
printf("Sending to hostname %s port %d\n", host, port);
//现在将连接字符串格式化一下，现在还没有发送
len = MQTTSerialize\_connect(buf, buflen, &data);
printf("%s",buf);
//现在是数据的发送
rc = transport\_sendPacketBuffer(mysock, buf, len);
/\* 等待connack \*///发送后接收服务器返回的数据，这里使用了一个函数的指针，要定义这个指针
if (MQTTPacket\_read(buf, buflen, transport_getdata) == CONNACK)//CONNACK – 确认连接请求
{
unsigned char sessionPresent, connack_rc
if (MQTTDeserialize\_connack(&sessionPresent, &connack_rc, buf, buflen) != 1 || connack_rc != 0)
{
printf("Unable to connect, return code %d\n", connack_rc);
goto exit;
}
}
else
goto exit;
/\* 订阅 \*/
topicString.cstring = "substopic";
len = MQTTSerialize\_subscribe(buf, buflen, 0, msgid, 1, &topicString, &req_qos);
rc = transport\_sendPacketBuffer(mysock, buf, len);
//等待服务器答复
//SUBACK 订阅确认 报文包含一个返回码清单， 它们指定了 SUBSCRIBE 请求的每个订阅被授予的最大 QoS 等级。
if (MQTTPacket\_read(buf, buflen, transport_getdata) == SUBACK) /\* 等待 suback \*/
{
unsigned short submsgid;
int subcount;
int granted_qos;
rc = MQTTDeserialize\_suback(&submsgid, 1, &subcount, &granted_qos, buf, buflen);
if (granted_qos != 0)
{
printf("granted qos != 0, %d\n", granted_qos);
goto exit;
}
}
else
goto exit;
/\* 循环获取消息 on subscribed topic \*/
// topicString.cstring = "pubtopic";
// while (1)
{
/\* transport\_getdata() has a built-in 1 second timeout,
your mileage will vary \*/
if (MQTTPacket\_read(buf, buflen, transport_getdata) == PUBLISH)//qos 响应报文，当qos>0时才有响应
{
unsigned char dup;
int qos;
unsigned char retained;
unsigned short msgid;
int payloadlen_in;
unsigned char\* payload_in;
int rc;
MQTTString receivedTopic;
rc = MQTTDeserialize\_publish(&dup, &qos, &retained, &msgid, &receivedTopic,
&payload_in, &payloadlen_in, buf, buflen);
printf("message arrived %.\*s\n", payloadlen_in, payload_in); //消息到达
}
printf("publishing reading\n");//读取发布
//下面两行是用来发布消息。这里发布，上面订阅，就形成了一个循环。
len = MQTTSerialize\_publish(buf, buflen, 0, 0, 0, 0, topicString, (unsigned char\*)payload, payloadlen);
rc = transport\_sendPacketBuffer(mysock, buf, len);
delay\_ms(1000);
}
while(1)
{
len = MQTTSerialize\_pingreq(buf, buflen);//发送心跳
rc = transport\_sendPacketBuffer(mysock, buf, len);//发送
delay\_s(55);
printf("心跳");
}
exit:
transport\_close(mysock);
MQTT实质上只是一个协议，搞清楚什么是订阅什么是发布，如何保持连接。
鉴于网友要求现在提供工程文件：
链接：pan.baidu.com/s/1OiG0CdIu…
提取码：d5ni
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