Arduino ESP32向EMQX发布消息的代码

好的，以下是Arduino ESP32向EMQX发布消息的代码：

#include <WiFi.h>
#include <PubSubClient.h>

// 连接到Wi-Fi网络
const char* ssid = "your_SSID";
const char* password = "your_PASSWORD";
WiFiClient espClient;
PubSubClient client(espClient);
const char* mqtt_server = "your_MQTT_broker_address";

void setup() {
  Serial.begin(115200);
  Serial.println("Connecting to Wi-Fi");
  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());

  // 连接到MQTT broker
  client.setServer(mqtt_server, 1883);
  while (!client.connected()) {
    Serial.println("Connecting to MQTT Broker...");
    if (client.connect("ESP32Client")) {
      Serial.println("MQTT Broker Connected");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      delay(5000);
    }
  }
}

void loop() {
  // 发布消息
  char message[50];
  snprintf (message, 50, "Hello from ESP32");
  client.publish("testTopic", message);
  delay(1000);
}

请注意，你需要修改代码中的 `your_SSID` ， `your_PASSWORD` 和 `your_MQTT_broker_address` 分别为你的Wi-Fi SSID，Wi-Fi密码和MQTT broker的ip地址或域名。还需要安装 PubSubClient 库，该库可在 Arduino IDE 中的“库管理器”中进行安装。