广播通信

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);
    }
}

完整源代码如下：（可运行）

sender.cpp:

/////////////////////////////////////////
// sender.cpp文件

#include "initsock.h"
#include "stdio.h"
#include <windows.h>

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 <windows.h>

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);
        }
    }
}