void Transport(int *p) { int t = 0; for (int i = 0; i < 3; i++) { for (int j = i; j < 3; j++) { t = *(p + (i * 3) + j); *(p + (i * 3) + j) = *(p + (j * 3) + i); *(p + (j * 3) + i) = t; } } }

你的问题是一个函数，我理解您想问这个函数的作用是什么。这个函数实现了一个矩阵的转置，它将一个3x3的矩阵沿主对角线进行转置。具体地说，它通过交换矩阵中第i行第j列的元素和第j行第i列的元素，来实现矩阵的转置。

相关问题

UEC++编写实现MQTT协议

MQTT（Message Queuing Telemetry Transport）是一个轻量级的、基于发布/订阅模式的通讯协议，被广泛应用于物联网等领域。下面是一个使用UEC++编写实现MQTT协议的示例：

#include <iostream>
#include <string>
#include <cstring>
#include <map>
#include <vector>

using namespace std;

// 定义MQTT消息类型
enum MqttMessageType {
  CONNECT = 1,
  CONNACK,
  PUBLISH,
  PUBACK,
  PUBREC,
  PUBREL,
  PUBCOMP,
  SUBSCRIBE,
  SUBACK,
  UNSUBSCRIBE,
  UNSUBACK,
  PINGREQ,
  PINGRESP,
  DISCONNECT
};

// 定义MQTT连接状态
enum MqttConnectStatus {
  CONNECT_ACCEPTED = 0,
  CONNECT_REFUSED_PROTOCOL,
  CONNECT_REFUSED_ID,
  CONNECT_REFUSED_SERVER,
  CONNECT_REFUSED_USER,
  CONNECT_REFUSED_PWD
};

// 定义MQTT消息结构体
struct MqttMessage {
  MqttMessageType type;
  bool dup;
  int qos;
  bool retain;
  int length;
  string topic;
  string payload;
  int packet_id;
  map<string, string> properties;
};

// 定义MQTT连接结构体
struct MqttConnect {
  string protocol_name;
  int protocol_version;
  bool clean_session;
  bool will_flag;
  int will_qos;
  bool will_retain;
  string will_topic;
  string will_message;
  string client_id;
  string username;
  string password;
  map<string, string> properties;
};

// 定义MQTT客户端类
class MqttClient {
public:
  MqttClient(const string& broker_url, int broker_port);
  ~MqttClient();
  bool connect(const MqttConnect& connect);
  bool publish(const MqttMessage& message);
  bool subscribe(const vector<string>& topics);
  bool unsubscribe(const vector<string>& topics);
  void disconnect();
private:
  bool send_message(const MqttMessage& message);
  bool read_message(MqttMessage& message);
  string broker_url_;
  int broker_port_;
  int socket_fd_;
  int packet_id_;
};

// 构造函数
MqttClient::MqttClient(const string& broker_url, int broker_port)
  : broker_url_(broker_url), broker_port_(broker_port), socket_fd_(-1), packet_id_(1) {}

// 析构函数
MqttClient::~MqttClient() {
  disconnect();
}

// 连接到MQTT服务器
bool MqttClient::connect(const MqttConnect& connect) {
  // 建立TCP连接
  socket_fd_ = socket(AF_INET, SOCK_STREAM, 0);
  if (socket_fd_ < 0) {
    cerr << "Failed to create socket." << endl;
    return false;
  }
  struct sockaddr_in broker_addr;
  memset(&broker_addr, 0, sizeof(broker_addr));
  broker_addr.sin_family = AF_INET;
  broker_addr.sin_port = htons(broker_port_);
  broker_addr.sin_addr.s_addr = inet_addr(broker_url_.c_str());
  if (connect(socket_fd_, (struct sockaddr*)&broker_addr, sizeof(broker_addr)) < 0) {
    cerr << "Failed to connect to broker." << endl;
    return false;
  }
  // 发送CONNECT消息
  MqttMessage message;
  message.type = CONNECT;
  message.qos = 0;
  message.properties["protocol_name"] = connect.protocol_name;
  message.properties["protocol_version"] = to_string(connect.protocol_version);
  message.properties["clean_session"] = connect.clean_session ? "1" : "0";
  message.properties["client_id"] = connect.client_id;
  message.properties["will_flag"] = connect.will_flag ? "1" : "0";
  message.properties["will_qos"] = to_string(connect.will_qos);
  message.properties["will_retain"] = connect.will_retain ? "1" : "0";
  message.properties["will_topic"] = connect.will_topic;
  message.properties["will_message"] = connect.will_message;
  message.properties["username"] = connect.username;
  message.properties["password"] = connect.password;
  message.properties.insert(connect.properties.begin(), connect.properties.end());
  if (!send_message(message)) {
    cerr << "Failed to send CONNECT message." << endl;
    return false;
  }
  // 读取CONNACK消息
  MqttMessage connack;
  if (!read_message(connack) || connack.type != CONNACK) {
    cerr << "Failed to receive CONNACK message." << endl;
    return false;
  }
  if (connack.properties["connect_status"] != to_string(CONNECT_ACCEPTED)) {
    cerr << "Connect refused: " << connack.properties["connect_status"] << endl;
    return false;
  }
  return true;
}

// 发布MQTT消息
bool MqttClient::publish(const MqttMessage& message) {
  // 发送PUBLISH消息
  MqttMessage publish_msg = message;
  publish_msg.type = PUBLISH;
  publish_msg.dup = false;
  publish_msg.packet_id = packet_id_++;
  if (!send_message(publish_msg)) {
    cerr << "Failed to send PUBLISH message." << endl;
    return false;
  }
  // 读取PUBACK消息
  if (message.qos == 1) {
    MqttMessage puback;
    if (!read_message(puback) || puback.type != PUBACK || puback.packet_id != publish_msg.packet_id) {
      cerr << "Failed to receive PUBACK message." << endl;
      return false;
    }
  }
  return true;
}

// 订阅MQTT主题
bool MqttClient::subscribe(const vector<string>& topics) {
  // 构造SUBSCRIBE消息
  MqttMessage message;
  message.type = SUBSCRIBE;
  message.qos = 1;
  message.packet_id = packet_id_++;
  for (auto topic : topics) {
    message.properties["topic"] = topic;
    message.properties["qos"] = "1";
  }
  if (!send_message(message)) {
    cerr << "Failed to send SUBSCRIBE message." << endl;
    return false;
  }
  // 读取SUBACK消息
  MqttMessage suback;
  if (!read_message(suback) || suback.type != SUBACK || suback.packet_id != message.packet_id) {
    cerr << "Failed to receive SUBACK message." << endl;
    return false;
  }
  return true;
}

// 取消订阅MQTT主题
bool MqttClient::unsubscribe(const vector<string>& topics) {
  // 构造UNSUBSCRIBE消息
  MqttMessage message;
  message.type = UNSUBSCRIBE;
  message.qos = 1;
  message.packet_id = packet_id_++;
  for (auto topic : topics) {
    message.properties["topic"] = topic;
  }
  if (!send_message(message)) {
    cerr << "Failed to send UNSUBSCRIBE message." << endl;
    return false;
  }
  // 读取UNSUBACK消息
  MqttMessage unsuback;
  if (!read_message(unsuback) || unsuback.type != UNSUBACK || unsuback.packet_id != message.packet_id) {
    cerr << "Failed to receive UNSUBACK message." << endl;
    return false;
  }
  return true;
}

// 断开MQTT连接
void MqttClient::disconnect() {
  if (socket_fd_ >= 0) {
    MqttMessage message;
    message.type = DISCONNECT;
    send_message(message);
    close(socket_fd_);
    socket_fd_ = -1;
  }
}

// 发送MQTT消息
bool MqttClient::send_message(const MqttMessage& message) {
  // 构造消息头
  char header[5];
  int pos = 0;
  header[pos++] = (message.type << 4) | (message.dup << 3) | (message.qos << 1) | message.retain;
  do {
    uint8_t digit = message.length % 128;
    message.length /= 128;
    if (message.length > 0) {
      digit |= 0x80;
    }
    header[pos++] = digit;
  } while (message.length > 0);
  // 发送消息头
  if (write(socket_fd_, header, pos) != pos) {
    return false;
  }
  // 发送消息体
  if (write(socket_fd_, message.topic.c_str(), message.topic.length()) != message.topic.length() ||
      (message.qos > 0 && write(socket_fd_, &message.packet_id, sizeof(message.packet_id)) != sizeof(message.packet_id)) ||
      write(socket_fd_, message.payload.c_str(), message.payload.length()) != message.payload.length()) {
    return false;
  }
  return true;
}

// 读取MQTT消息
bool MqttClient::read_message(MqttMessage& message) {
  // 读取消息头
  char header[5];
  int pos = 0;
  while (pos < 2) {
    int ret = read(socket_fd_, header + pos, 2 - pos);
    if (ret <= 0) {
      return false;
    }
    pos += ret;
  }
  message.type = static_cast<MqttMessageType>((header[0] & 0xf0) >> 4);
  message.dup = (header[0] & 0x08) != 0;
  message.qos = (header[0] & 0x06) >> 1;
  message.retain = (header[0] & 0x01) != 0;
  message.length = 0;
  for (int i = 1; i < pos; ++i) {
    message.length = (message.length << 7) | (header[i] & 0x7f);
    if ((header[i] & 0x80) == 0) {
      break;
    }
  }
  // 读取消息体
  int payload_len = message.length;
  if (message.qos > 0) {
    payload_len -= sizeof(message.packet_id);
  }
  char* payload_buf = new char[payload_len];
  pos = 0;
  while (pos < payload_len) {
    int ret = read(socket_fd_, payload_buf + pos, payload_len - pos);
    if (ret <= 0) {
      delete[] payload_buf;
      return false;
    }
    pos += ret;
  }
  message.topic = string(payload_buf, payload_len);
  if (message.qos > 0) {
    memcpy(&message.packet_id, payload_buf + payload_len, sizeof(message.packet_id));
    message.payload = string(payload_buf + payload_len + sizeof(message.packet_id), message.length - payload_len - sizeof(message.packet_id));
  } else {
    message.payload = string(payload_buf + payload_len, message.length - payload_len);
  }
  delete[] payload_buf;
  return true;
}

int main() {
  MqttConnect connect;
  connect.protocol_name = "MQTT";
  connect.protocol_version = 4;
  connect.clean_session = true;
  connect.client_id = "test_client";
  MqttClient client("localhost", 1883);
  if (client.connect(connect)) {
    MqttMessage message;
    message.qos = 1;
    message.topic = "test_topic";
    message.payload = "hello world";
    client.publish(message);
    client.subscribe({"test_topic"});
    client.unsubscribe({"test_topic"});
    client.disconnect();
  }
  return 0;
}

这段代码实现了MQTT客户端的基本功能，包括连接到MQTT服务器、发布消息、订阅主题和取消订阅主题等。其中，send_message函数用于发送MQTT消息，read_message函数用于读取MQTT消息。MQTT消息的格式和消息头的解析方式参考MQTT协议规范。

STM32f103+ENC28J60实现PC与开发板udp收发数据代码

以下是基于STM32f103和ENC28J60实现PC与开发板UDP收发数据的示例代码：

首先需要安装lwIP网络协议栈。在创建工程时，选择使用lwIP，然后选择相应的网络接口。在我的例子中，我使用了ENC28J60作为网络接口。

接下来，需要配置lwIP。在lwIP的配置文件（lwipopts.h）中，需要设置以下参数：

#define LWIP_UDP                1
#define LWIP_NETIF_API          1
#define LWIP_NETIF_HOSTNAME     1
#define IP_SOF_BROADCAST        1
#define IP_SOF_BROADCAST_RECV   1

这些参数启用了UDP协议、lwIP API、主机名和广播功能。

接着，在main.c中初始化网络接口：

#include "lwip/init.h"
#include "lwip/netif.h"
#include "netif/etharp.h"
#include "enc28j60.h"

struct netif gnetif;

int main(void)
{
    /* Initialize lwIP */
    lwip_init();

    /* Initialize ENC28J60 */
    enc28j60_init();

    /* Add ENC28J60 interface */
    netif_add(&gnetif, NULL, NULL, NULL, NULL, enc28j60_init_eth, ethernet_input);

    /* Set ENC28J60 interface up */
    netif_set_up(&gnetif);

    /* Start DHCP client */
    dhcp_start(&gnetif);

    /* Main loop */
    while(1)
    {
        /* Process lwIP timers */
        sys_check_timeouts();

        /* Process incoming packets */
        ethernetif_input(&gnetif);
    }
}

在初始化lwIP后，我们需要初始化ENC28J60，并添加网络接口。然后将网络接口设置为活动状态，并启动DHCP客户端。

现在我们可以开始实现UDP数据包的收发。以下是发送UDP数据包的代码：

#include "lwip/udp.h"

#define SERVER_IP_ADDR  IP_ADDR_BROADCAST
#define SERVER_PORT     1234

void udp_send_data(void)
{
    struct udp_pcb *pcb;
    struct pbuf *p;
    err_t err;

    /* Create a new UDP PCB */
    pcb = udp_new();

    /* Allocate a pbuf for the data to be sent */
    p = pbuf_alloc(PBUF_TRANSPORT, sizeof("Hello, world!"), PBUF_RAM);
    memcpy(p->payload, "Hello, world!", sizeof("Hello, world!"));

    /* Send the UDP packet */
    err = udp_sendto(pcb, p, IP_ADDR_BROADCAST, SERVER_PORT);

    /* Free the pbuf */
    pbuf_free(p);

    /* Free the UDP PCB */
    udp_remove(pcb);
}

这个例子中，我们创建了一个新的UDP PCB，并分配了一个pbuf用于发送数据。然后，我们使用udp_sendto函数将数据发送到广播地址。

以下是接收UDP数据包的代码：

#include "lwip/udp.h"

#define CLIENT_PORT     4321

void udp_recv_callback(void *arg, struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *addr, u16_t port)
{
    /* Process the received data */
    printf("Received data: %s\n", p->payload);

    /* Free the pbuf */
    pbuf_free(p);
}

void udp_recv_data(void)
{
    struct udp_pcb *pcb;
    err_t err;

    /* Create a new UDP PCB */
    pcb = udp_new();

    /* Bind the UDP PCB to a local port */
    err = udp_bind(pcb, IP_ADDR_ANY, CLIENT_PORT);

    /* Set the receive callback function */
    udp_recv(pcb, udp_recv_callback, NULL);

    /* Main loop */
    while(1)
    {
        /* Process lwIP timers */
        sys_check_timeouts();

        /* Process incoming packets */
        ethernetif_input(&gnetif);
    }

    /* Free the UDP PCB */
    udp_remove(pcb);
}

这个例子中，我们创建了一个新的UDP PCB，并将其绑定到本地端口。然后，我们设置了一个回调函数来处理接收到的数据。

在主循环中，我们需要定期调用sys_check_timeouts函数来处理lwIP定时器，并调用ethernetif_input函数来处理接收到的数据包。

以上便是基于STM32f103和ENC28J60实现PC与开发板UDP收发数据的示例代码。