c mqtt 接收到服务器消息后返回一个topic 消息
时间: 2024-04-09 10:29:15 浏览: 13
在 C 语言中,你可以使用 MQTT 客户端库来接收来自服务器的消息并返回相应的主题和消息。以下是一个使用 Eclipse Paho MQTT C 客户端库的示例代码:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
#define ADDRESS "tcp://mqtt.eclipse.org:1883"
#define CLIENTID "ExampleClientSub"
#define TOPIC "testtopic"
#define QOS 1
#define TIMEOUT 10000L
volatile MQTTClient_deliveryToken deliveredtoken;
int msgarrvd(void *context, char *topicName, int topicLen, MQTTClient_message *message)
{
printf("接收到消息!\n");
printf("主题: %s\n", topicName);
printf("消息: ");
fwrite(message->payload, 1, message->payloadlen, stdout);
printf("\n");
MQTTClient_freeMessage(&message);
MQTTClient_free(topicName);
return 1;
}
void connlost(void *context, char *cause)
{
printf("\n连接丢失!\n");
printf("原因: %s\n", cause);
}
int main(int argc, char* argv[])
{
MQTTClient client;
MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
int rc;
MQTTClient_create(&client, ADDRESS, CLIENTID,
MQTTCLIENT_PERSISTENCE_NONE, NULL);
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;
MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered);
if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
{
printf("连接到 MQTT 服务器失败, 返回代码: %d\n", rc);
exit(EXIT_FAILURE);
}
printf("连接到 MQTT 服务器成功!\n");
printf("订阅主题: %s\n", TOPIC);
MQTTClient_subscribe(client, TOPIC, QOS);
while (1)
;
MQTTClient_disconnect(client, 10000);
MQTTClient_destroy(&client);
return rc;
}
```
在这个示例代码中,我们使用 Eclipse Paho MQTT C 客户端库连接到 MQTT 服务器并订阅指定的主题。当收到来自服务器的消息时,会调用 `msgarrvd` 函数来处理消息并返回主题和消息内容。
请注意,你需要提前安装 Eclipse Paho MQTT C 客户端库,并在编译时链接相应的库文件。具体的安装和编译步骤可以参考该库的文档或官方网站。