stm32标准库的MQTT客户端代码

下面是使用STM32标准库的MQTT客户端代码示例：

#include "stm32f4xx.h"
#include "mqtt_client.h"
#include <string.h>

#define MQTT_HOST "test.mosquitto.org"
#define MQTT_PORT 1883
#define MQTT_TOPIC "test"
#define MQTT_CLIENT_ID "STM32F4"

uint8_t mqtt_buffer[1024];
uint8_t mqtt_read_buffer[1024];

/* Callback function for MQTT messages */
void message_callback(MessageData* data)
{
    MQTTMessage* message = data->message;
    char payload[message->payloadlen + 1];
    memcpy(payload, message->payload, message->payloadlen);
    payload[message->payloadlen] = '\0';
    printf("Received message: %s\n", payload);
}

int main(void)
{
    Network network;
    MQTTClient client;
    int rc;

    /* Initialize network interface */
    NewNetwork(&network);

    /* Connect to MQTT broker */
    rc = ConnectNetwork(&network, MQTT_HOST, MQTT_PORT);
    if (rc != 0) {
        printf("Failed to connect to MQTT broker. Error code: %d\n", rc);
        return -1;
    }

    /* Initialize MQTT client */
    MQTTClientInit(&client, &network, 30000, mqtt_buffer, sizeof(mqtt_buffer), mqtt_read_buffer, sizeof(mqtt_read_buffer));

    /* Set MQTT client callbacks */
    client.messageHandlers[0].topicFilter = MQTT_TOPIC;
    client.messageHandlers[0].qos = QOS0;
    client.messageHandlers[0].fp = message_callback;

    /* Connect to MQTT broker */
    MQTTPacket_connectData connect_data = MQTTPacket_connectData_initializer;
    connect_data.clientID.cstring = MQTT_CLIENT_ID;
    rc = MQTTConnect(&client, &connect_data);
    if (rc != 0) {
        printf("Failed to connect to MQTT broker. Error code: %d\n", rc);
        return -1;
    }

    /* Subscribe to MQTT topic */
    rc = MQTTSubscribe(&client, MQTT_TOPIC, QOS0, message_callback);
    if (rc != 0) {
        printf("Failed to subscribe to MQTT topic. Error code: %d\n", rc);
        return -1;
    }

    /* Publish message to MQTT broker */
    MQTTMessage message;
    char payload[] = "Hello, world!";
    message.qos = QOS0;
    message.retained = 0;
    message.payload = payload;
    message.payloadlen = strlen(payload);
    rc = MQTTPublish(&client, MQTT_TOPIC, &message);
    if (rc != 0) {
        printf("Failed to publish message to MQTT broker. Error code: %d\n", rc);
        return -1;
    }

    /* Wait for MQTT messages */
    while (1) {
        MQTTYield(&client, 1000);
    }

    return 0;
}

上述代码依赖于标准库中的网络、MQTT客户端和MQTT包库。在使用此代码之前，请确保已经正确配置了网络和MQTT客户端库。