C/C++ Socket UDP 广播消息的发送与接收

C/C++ Socket UDP 广播消息的发送与接收

局域网内全网段广播消息的IP地址为：255.255.255.255，向该IP地址发送广播消息，局域网下的任何网段的客户机都能收到广播。

对于发送端，如果你只想给某个特定的网段发送消息，例如你的IP地址为192.168.31.107，那么你的广播地址是192.168.31.255，向该广播地址发送广播消息，只有192.168.31.XXX网段下的客户机能收到广播。

同样，对于接收端，绑定了广播地址0.0.0.0这个IP即可。

C语言 UDP 广播简单示例（linux系统下）：

/*
 * main.c
 *
 *  Created on: Sep 26, 2022
 *      Author: root
 */

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>

#define BOARDCAST_IP     "255.255.255.255"
#define BOARDCAST_PORT   10130

int broadcast_send(void)
{
  int fd;
  int ret;
  int on;
  struct sockaddr_in addr;
  const char* message = "This is boardcast message !";

  fd = socket(AF_INET, SOCK_DGRAM, 0);

  if(fd < 0)
  {
    fprintf(stderr, " create socket failed ! \n");
    goto __exit;
  }

  on = 1;
  ret = setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &on, sizeof(on));
  if(ret < 0)
  {
    fprintf(stderr, " setsockopt failed ! \n");
    goto __exit;
  }

  memset(&addr, 0, sizeof(addr));

  addr.sin_family = AF_INET;
  addr.sin_port = htons(BOARDCAST_PORT);
  addr.sin_addr.s_addr = inet_addr(BOARDCAST_IP);

  ret = sendto(fd, message, strlen(message), 0, (struct sockaddr *)&addr, sizeof(addr));
  if(fd < 0)
  {
    fprintf(stderr, " boardcast failed ! \n");
    goto __exit;
  }

  printf(" send ok ! \n");

__exit:
  close(fd);
  return 0;
}

int broadcast_recv(void)
{
  int fd;
  int ret;
  int on;
  struct sockaddr_in addr, addr_from;
  char message[512];
  socklen_t len;

  fd = socket(AF_INET, SOCK_DGRAM, 0);

  if(fd < 0)
  {
    fprintf(stderr, " create socket failed ! \n");
    goto __exit;
  }

  on = 1;
  ret = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
  if(ret < 0)
  {
    fprintf(stderr, " setsockopt failed ! \n");
    goto __exit;
  }

  memset(&addr, 0, sizeof(addr));

  addr.sin_family = AF_INET;
  addr.sin_port = htons(BOARDCAST_PORT);
  addr.sin_addr.s_addr = htonl(INADDR_ANY);

  ret = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
  if(ret < 0)
  {
    fprintf(stderr, " bind failed ! \n");
    goto __exit;
  }

  memset(message, 0X00, sizeof(message));

  len = sizeof(addr_from);
  ret = recvfrom(fd, message, sizeof(message), 0, (struct sockaddr *)&addr_from, &len);
  if(ret < 0)
  {
    fprintf(stderr, " recv failed ! \n");
    goto __exit;
  }

  printf(" recv: [%s] ok ! \n", message);

__exit:
  close(fd);
  return 0;
}

int main(int argc, const char* argv[])
{
  if(argc == 2)
  {
    if(strcmp(argv[1], "recv") == 0)
    {
      broadcast_recv();
    }

    if(strcmp(argv[1], "send") == 0)
    {
      broadcast_send();
    }
  }else
  {
    printf("\r\n");
    printf("########################################### \r\n");
    printf("Usage: %s [ recv | send ] \r\n", argv[0]);
    printf("e.g. : %s recv\r\n", argv[0]);
    printf("e.g. : %s send\r\n", argv[0]);
    printf("########################################### \r\n");
  }

  return 0;
}

程序运行结果：

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