关于udp的广播和普通链接

今天在工作的时候遇到了一个问题，将一个socket  bind到一个SOCKADDR_IN上后，广播不出去。后来查找资料发现广播需要使用两个SOCKADDR_IN。一个SOCKADDR_IN用来bind  socket，一个SOCKADDR_IN在sendto的时候使用。具体代码如下：

广播客户端：

#pragma comment(lib, "ws2_32.lib")


int _tmain(int argc, _TCHAR* argv[])
{
	
	WORD wVersionRequested;
	WSADATA wsaData;         //指向WinSocket信息结构的指针
    SOCKET sockListener;
    SOCKADDR_IN sin,saClient;
    char cRecvBuff[2000];
    int nSize,nbSize;
    int iAddrLen=sizeof(saClient);
	bool bOpt = true;
	 // 启动socket api
    wVersionRequested = MAKEWORD( 2, 2 );
	int err = WSAStartup( wVersionRequested, &wsaData );
	if ( err != 0 )
	{
		return -1;
	}

	if ( LOBYTE( wsaData.wVersion ) != 2 || HIBYTE( wsaData.wVersion ) != 2 )
	{
		WSACleanup( );
		return -1;
	}
	// 创建socket
    sockListener=socket(AF_INET, SOCK_DGRAM,0);
	setsockopt(sockListener,SOL_SOCKET, SO_BROADCAST, (char*)&bOpt, sizeof(bOpt));
	// 用来绑定套接字
    sin.sin_family = AF_INET;
    sin.sin_port = htons(7001);//发送端使用的发送端口，可以根据需要更改
    sin.sin_addr.s_addr = 0;
	// 用来从网络上的广播地址接收数据
	saClient.sin_family = AF_INET;
	saClient.sin_port = htons(7001);
	saClient.sin_addr.S_un.S_addr = INADDR_BROADCAST;
    if(bind( sockListener, (SOCKADDR FAR *)&sin, sizeof(sin))!=0)
    {
        printf("Can't bind socket to local port!Program stop.\n");//初始化失败返回-1
        return -1;
    }
    while(1)
    {// 接收数据
        nSize = sizeof ( SOCKADDR_IN );
        if((nbSize=recvfrom (sockListener,cRecvBuff,2000,0,(SOCKADDR FAR *) &saClient,&nSize))==SOCKET_ERROR)
        {
            printf("Recive Error");
			Sleep(10000);
            break;
        }
        cRecvBuff[nbSize] = '\0';
        printf("%s\n",cRecvBuff);
	}
    return 0;
}

广播服务器端：

#include "stdafx.h"
#include <string.h>
#pragma comment(lib, "ws2_32.lib")


int _tmain(int argc, _TCHAR* argv[])
{

<span style="white-space:pre">	</span>WSADATA wsaData;          //指向WinSocket信息结构的指针
    SOCKET sockListener;
    SOCKADDR_IN sin,saUdpServ;
    BOOL fBroadcast = TRUE;
    char sendBuff[1024];
    int nSize;
    int ncount=0;
    if(WSAStartup(MAKEWORD( 1, 1 ), &wsaData )!=0)//进行WinSocket的初始化
    {
        printf("Can't initiates windows socket!Program stop.\n");//初始化失败返回-1
        return -1;
    }
    sockListener=socket(PF_INET,SOCK_DGRAM,0);
    setsockopt ( sockListener,SOL_SOCKET,SO_BROADCAST,(CHAR *)&fBroadcast,sizeof ( BOOL ));
    sin.sin_family = AF_INET;
    sin.sin_port = htons(0);
    sin.sin_addr.s_addr = htonl(INADDR_ANY);
    if(bind( sockListener, (SOCKADDR *)&sin, sizeof(sin))!=0)
    {
        printf("Can't bind socket to local port!Program stop.\n");//初始化失败返回-1
        return -1;
    }
    saUdpServ.sin_family = AF_INET;
    saUdpServ.sin_addr.s_addr = htonl ( INADDR_BROADCAST );
    saUdpServ.sin_port = htons (7001);//发送用的端口，可以根据需要更改
    nSize = sizeof ( SOCKADDR_IN );
    while(1)
    {
        sprintf_s(sendBuff,"Message %d",ncount++);
        sendto ( sockListener,sendBuff,lstrlen (sendBuff),0,(SOCKADDR *) &saUdpServ,sizeof ( SOCKADDR_IN ));
        printf("%s\n",sendBuff);
    }
	return 0;
}