公开的mqtt服务器如何获得等问题

让阿豪来帮你解答，本回答参考chatgpt3.5编写提供，如果还有疑问可以评论或留言

1. 初始化MQTT客户端

#include 
#include 
const char* ssid = "your_SSID";
const char* password = "your_PASSWORD";
const char* mqtt_server = "your_MQTT_SERVER";
WiFiClient espClient;
PubSubClient client(espClient);
void setup_wifi() {
  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}
void setup() {
  Serial.begin(115200);
  setup_wifi();
  client.setServer(mqtt_server, 1883);
}
void loop() {
  if (!client.connected()) {
    reconnect();
  }
  client.loop();
}
void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Create a random client ID
    String clientId = "ESP32Client-";
    clientId += String(random(0xffff), HEX);
    // Attempt to connect
    if (client.connect(clientId.c_str())) {
      Serial.println("connected");
      // Once connected, publish an announcement...
      client.publish("outTopic", "hello world");
      // ... and resubscribe
      client.subscribe("inTopic");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

1. 发布消息到MQTT服务器

client.publish("topic_name", "message_payload");

1. 订阅MQTT服务器的消息

client.subscribe("topic_name");

参考文献： 阿里云MQTT客户端https://help.aliyun.com/document_detail/96818.html MQTT客户端代码示例https://github.com/adafruit/Adafruit_MQTT_Library/tree/master/examples/MQTT_ESP32_Example

阿里云提供了公开的MQTT服务器，可以免费使用。通过阿里云MQTT服务，用户可以实现设备与云端的双向通信，方便进行数据传输和控制操作。

// 以STM32单片机为例，使用WiFi模块连接阿里云MQTT服务器的代码示例#include <
WiFi.h>
#include <
PubSubClient.h>
 
const char* ssid = "
your-ssid"
;
const char* password = "
your-password"
;
const char* mqtt_server = "
mqtt.aliyun.com"
;
const int mqtt_port = 1883;
 
WiFiClient espClient;
PubSubClient client(espClient);
 
void setup() {WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {delay(500);
}client.setServer(mqtt_server, mqtt_port);
} 
void loop() {if (!client.connected()) {reconnect();
}client.loop();
// other code here} 
void reconnect() {while (!client.connected()) {if (client.connect("
client-id"
, "
your-username"
, "
your-password"
)) {// Subscribe to a topicclient.subscribe("
topic/sub"
);
} else {delay(5000);
}}}

通过以上代码示例，可以实现STM32单片机连接到阿里云MQTT服务器并订阅指定的主题进行通信。阿里云的MQTT服务器提供了稳定的通信服务，方便开发者进行物联网项目的开发和实现。