广播：可以把数据发送给本地子网上的每个机器。

如果多个进程都发送广播数据，网络就会阻塞

对于UDP来说，存在一个特定的广播地址，255.255.255.255

 

发送方程序在创建套接字后使用setsockopt函数打开SO_BROADCAST选项，然后设置广播地址255.255.255.255,向端口号4567不断发送广播数据。

发送代码如下：

SOCKET s = ::socket(AF_INET,SOCK_DGRAM,0);//有效的SO_BROADCAST选项BOOL bBroadcast = TRUE;::setsockopt(s,SOL_SOCKET,SO_BROADCAST,(char*)&bBroadcast,sizeof(BOOL));//设置广播地址SOCKADDR_IN bcast;bcast.sin_family = AF_INET;bcast.sin_addr.s_addr = INADDR_BROADCAST;bcast.sin_port = htons(4567);//发送广播printf("开始向4567发送广播数据...\n");char sz[] = "this is just a test.\n";while(TRUE){    ::sendto(s,sz,strlen(sz),0,(sockaddr*)&bcast,sizeof(bcast));    ::Sleep(5000);}

接收方代码：

SOCKET s = ::socket(AF_INET,SOCK_DGRAM,0);//绑定一个本地地址，指明广播端口号SOCKADDR_IN sin;sin.sin_family = AF_INET;sin.sin_addr.S_un.S_addr = INADDR_ANY;sin.sin_port = ::ntohs(4567);if(::bind(s,(sockaddr*)&sin,&sizeof(sin))==SOCKET_ERROR){    printf("bind() failed!\n");    return;}//接收广播printf("开始在4567接收广播数据...\n");char sz[256];while(TRUE){    int nRet = ::recvfrom(s,sz,256,0,(sockaddr*)&addRemote,&nLen);    if(nRet>0)    {        sz[nRet] = '\0';        printf(sz);    }}

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完整源代码如下：（可运行）

sender.cpp:

/////// sender.cpp文件#include "initsock.h"#include "stdio.h"#include 
     
      CInitSock theSock;void main(){    SOCKET s = ::socket(AF_INET, SOCK_DGRAM, 0);    // 有效SO_BROADCAST选项    BOOL bBroadcast = TRUE;    ::setsockopt(s, SOL_SOCKET, SO_BROADCAST, (char*)&bBroadcast, sizeof(BOOL));    // 设置广播地址，这里的广播端口号（电台）是4567    SOCKADDR_IN bcast;    bcast.sin_family = AF_INET;    bcast.sin_addr.s_addr = INADDR_BROADCAST; // ::inet_addr("255.255.255.255");    bcast.sin_port = htons(4567);    // 发送广播    printf(" 开始向4567端口发送广播数据... \n \n");    char sz[] = "This is just a test. \r\n";    while(TRUE)    {        ::sendto(s, sz, strlen(sz), 0, (sockaddr*)&bcast, sizeof(bcast));        ::Sleep(5000);    }}/*    ::send(s, sz, strlen(sz), 0);    sockaddr_in addr;    addr.sin_family = AF_INET;    addr.sin_port = ntohs(3333);    addr.sin_addr.S_un.S_addr  = ADDR_ANY;    if(::bind(s, (sockaddr*)&addr, sizeof(addr)) == SOCKET_ERROR)    {        printf(" bind() failed \n");        return;    }  */
     

recver.cpp：

/////// recver.cpp文件#include "initsock.h"#include "stdio.h"#include 
     
      CInitSock theSock;void main(){    SOCKET s = ::socket(AF_INET, SOCK_DGRAM, 0);    // 首先要绑定一个本地地址，指明广播端口号    SOCKADDR_IN sin;    sin.sin_family = AF_INET;    sin.sin_addr.S_un.S_addr = INADDR_ANY;        sin.sin_port = ::ntohs(4567);    if(::bind(s, (sockaddr*)&sin, sizeof(sin)) == SOCKET_ERROR)    {        printf(" bind() failed \n");        return;    }    // 接收广播    printf(" 开始在4567端口接收广播数据... \n\n");    SOCKADDR_IN addrRemote;        int nLen = sizeof(addrRemote);    char sz[256];    while(TRUE)    {        int nRet = ::recvfrom(s, sz, 256, 0, (sockaddr*)&addrRemote, &nLen);        if(nRet > 0)        {            sz[nRet] = '\0';            printf(sz);        }    }}
     

运行结果：