客户端程序：

#include<stdlib.h>
#include<iostream.h>
#include<stdio.h>
#include<conio.h>
#include<winsock2.h>
#include<windows.h>

#pragma comment(lib,"ws2_32.lib")
main()
{
 SOCKET s;
 sockaddr_in addrto;
 WSADATA wsdata;
 BOOL bsocket;
 char *smsg="this is a test";
 //启动SOCKET库，版本为2.0
 WSAStartup(0x0202,&wsdata);
 
 s=WSASocket(AF_INET,SOCK_DGRAM,0,NULL,0,WSA_FLAG_OVERLAPPED);
 bsocket=TRUE;
    //然后赋值给地址，用来从网络上的广播地址接收消息；
 addrto.sin_family=AF_INET;
    addrto.sin_addr.s_addr=INADDR_BROADCAST;
 addrto.sin_port=htons(5050);
 bool opt=true;
 //设置该套接字为广播类型，
 setsockopt(s,SOL_SOCKET,SO_BROADCAST,(char FAR *)&opt,sizeof(opt));
 int nlen=sizeof(addrto);
 while(1)
 {
  Sleep(1000);
  //从广播地址发送消息
  int ret=sendto(s,smsg,256,0,(sockaddr*)&addrto,nlen);
  if(ret==SOCKET_ERROR)
   cout<<WSAGetLastError()<<endl;
  else
  {  
   printf("ok"); 
  }
 }
}

服务器程序:

#include<stdlib.h>
#include<iostream.h>
#include<conio.h>
#include<stdio.h>
#include<winsock2.h>
#include<windows.h>
#pragma comment(lib,"ws2_32.lib")

void main(void)
{
 SOCKET s;
 sockaddr_in from,a;
 WSADATA wsdata;
 BOOL optval;
 //启动SOCKET库，版本为2.0
 WSAStartup(0x0202,&wsdata);
 optval=TRUE;
 //然后赋值给两个地址，一个用来绑定套接字，一个用来从网络上的广播地址接收消息；
 a.sin_family=AF_INET;
 a.sin_addr.s_addr=0;
 a.sin_port=htons(5050);

 from.sin_family=AF_INET;
 from.sin_addr.s_addr=INADDR_BROADCAST;
 from.sin_port=htons(5050);
 
 int fromlength=sizeof(SOCKADDR);
 //用UDP初始化套接字
 s=socket(AF_INET,SOCK_DGRAM,0);
   //设置该套接字为广播类型，
 setsockopt(s,SOL_SOCKET,SO_BROADCAST,(char FAR *)&optval,sizeof(optval));
 bind(s,(sockaddr *)&a,sizeof(sockaddr_in));
 char buf[256];
 while(1)
 {//从广播地址接收消息，注意用来绑定的地址和接收消息的地址是不一样的
  recvfrom(s,buf,256,0,(struct sockaddr FAR *)&from,(int FAR *)&fromlength);
  Sleep(2000);
  printf("%s\n",buf);
  ZeroMemory(buf,256);
 }
}