Socket网络编程的广播用的地址是255.255.255.255，广播数据不会被路由器转发，限定于局域网内，否则就是网络风暴了。

广播的代码比较简单，直接参考单播/组播的例子写一个。

Server端的流程如下：

• 调用socket()打开一个Socket
• 调用bind()指定Port信息
• 调用setsockopt()加入广播
• 调用recvfrom()阻塞接收
• 最后，调用close()关闭Socket

 
#include "stdio.h" /* pritnf() */ 
#include "stdLib.h" /* malloc() */ 
#include "sockLib.h" /* socket() */ 
#include "inetLib.h" /* struct sockaddr_in */ 

 
#define HOST_PORT 60000 
#define MIN_SIZE 10 
#define MIN_TIMES 10 

 
void broadServer (int port, int size, int times) 
{ 
 struct sockaddr_in localAddr; 
 struct sockaddr_in peerAddr; 
 int addrSize = sizeof(struct sockaddr); 
 int opt = 1; 
 int fd; 
 int num; 
 char *buffer; 
 if(port <= 2000) port = HOST_PORT; 
 if(size <= 0) size = MIN_SIZE; 
 if(times <= 0) times = MIN_TIMES; 
 printf (" broadServer: try to receive %d chars from port %d\n", size, port); 
  
 /* 打开Socket */ 
 fd = socket (AF_INET, SOCK_DGRAM, 0); 
  
 /* 指定本地地址信息 */ 
 localAddr.sin_family = AF_INET; 
 localAddr.sin_port = htons (port); 
 localAddr.sin_addr.s_addr = INADDR_ANY; 
 bind (fd, (struct sockaddr *)&localAddr, sizeof(struct sockaddr)); 

 
/* 加入广播 */ 
 setsockopt(fd, SOL_SOCKET, SO_BROADCAST, (char *)&opt, sizeof(int)); 

 
buffer = (char *)malloc (size); 
 while ((times--)>0) 
 { 
 /* 接收广播数据 */ 
 num = recvfrom (fd, buffer, size, 0,  
 (struct sockaddr *)&peerAddr, &addrSize); 
 if (num < 0) break; 
 printf (" broadServer: recv %d chars from %s\n",  
 num, inet_ntoa(peerAddr.sin_addr)); 
 } 

 
/* 关闭Socket */ 
 close (fd); 
 free (buffer); 
 printf (" broadServer: end\n"); 
 } 

 

Client端的流程如下：

• 调用socket()打开一个Socket
• 指定广播地址和Port信息
• 调用sendto()发送数据
• 最后，调用close()关闭Socket

#include "stdio.h" /* pritnf() */
#include "stdLib.h" /* malloc() */
#include "sockLib.h" /* socket() */
#include "inetLib.h" /* struct sockaddr_in */

#define HOST_PORT 60000
#define MIN_SIZE 1
#define MIN_TIMES 1

void broadClient (int port, int size, int times)
{
struct sockaddr_in serverAddr;
int opt = 1;
int fd; 
char *buffer;
int num; 
if(port <= 2000) port = HOST_PORT;
if(size <= 0) size = MIN_SIZE;
if(times<= 0) times= MIN_TIMES;
buffer = (char *)malloc(size);
for(num=0; num<size; num++) buffer[num] = (num%26)+'a';

/* 服务器地址信息 */
serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons (port);
serverAddr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
printf (" broadClient: try to send %d chars %d times to %s:%d\n",
size, times, inet_ntoa(serverAddr.sin_addr), port);

/* 打开Socket */
fd = socket (AF_INET, SOCK_DGRAM, 0);

while ((times--)>0)
{
/* 发送数据到BroadCast Server */
num = sendto(fd, buffer, size, 0, 
(struct sockaddr *)&serverAddr, sizeof(struct sockaddr));
printf (" broadClient: send %d chars\n", num);
}

/* 关闭Socket */
close (fd);
free (buffer);
printf (" broadClient: send finished\n");
}

测试结果如下：