这次我将代码整合后，做一个实战的练习，扫描一个IP段，返回所有活动的IP

要完成这个练习，以下有几个步骤，作为程序员的我们就用代码说话
首先要做到如何证明一个IP是否在活动，代码如下
Java代码
BOOL IpCheck::IsIPActive(char *addr)
{
// 目的IP地址，即要Ping的IP地址
char *szDestIp = addr; // 127.0.0.1

// 创建原始套节字
WSADATA wsaData;
WSAStartup(MAKEWORD(2, 2), &wsaData);
SOCKET sRaw = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);

// 设置接收超时
SetTimeout(sRaw, 100, TRUE);

// 设置目的地址
SOCKADDR_IN dest;
dest.sin_family = AF_INET;
dest.sin_port = htons(0);
dest.sin_addr.S_un.S_addr = inet_addr(szDestIp);

// 创建ICMP封包
char buff[sizeof(ICMP_HDR) + 32];
ICMP_HDR* pIcmp = (ICMP_HDR*)buff;

// 填写ICMP封包数据，请求一个ICMP回显
pIcmp->icmp_type = 8;
pIcmp->icmp_code = 0;
pIcmp->icmp_id = (USHORT)GetCurrentProcessId();
pIcmp->icmp_checksum = 0;
pIcmp->icmp_sequence = 0;

// 填充数据部分，可以为任意
memset(&buff[sizeof(ICMP_HDR)], 'E', 32);

// 开始发送和接收ICMP封包
USHORT nSeq = 0;
char recvBuf[1024];
SOCKADDR_IN from;
int nLen = sizeof(from);

static int nCount = 0;
int nRet;

pIcmp->icmp_checksum = 0;
pIcmp->icmp_timestamp = GetTickCount();
pIcmp->icmp_sequence = nSeq++;
pIcmp->icmp_checksum = checksum((USHORT*)buff, sizeof(ICMP_HDR) + 32);
nRet = sendto(sRaw, buff, sizeof(ICMP_HDR) + 32, 0, (SOCKADDR *)&dest, sizeof(dest));
if(nRet == SOCKET_ERROR)
{
printf(" sendto() failed: %d \n", ::WSAGetLastError());
return -1;
}
nRet = recvfrom(sRaw, recvBuf, 1024, 0, (sockaddr*)&from, &nLen);
if(nRet == SOCKET_ERROR)
{
if(WSAGetLastError() == WSAETIMEDOUT)
{
printf("%s timed out\n", addr);
return FALSE;
}
printf("recvfrom() failed: %d\n", WSAGetLastError());
return FALSE;
}

// 下面开始解析接收到的ICMP封包
int nTick = ::GetTickCount();
if(nRet < sizeof(IPHeader) + sizeof(ICMP_HDR))
{
printf(" Too few bytes from %s \n", inet_ntoa(from.sin_addr));
}

// 接收到的数据中包含IP头，IP头大小为20个字节，所以加20得到ICMP头
// (ICMP_HDR*)(recvBuf + sizeof(IPHeader));
ICMP_HDR* pRecvIcmp = (ICMP_HDR*)(recvBuf + 20);
if(pRecvIcmp->icmp_type == ICMP_TYPE_REACH_FAIL) // 回显
{
printf("%s reach fail, type %d recvd \n", addr, pRecvIcmp->icmp_type);
return FALSE;
}

if(pRecvIcmp->icmp_id != GetCurrentProcessId())
{
printf(" someone else's packet! \n");
return FALSE;
}

printf("从 %s 返回 %d 字节:", addr,nRet);
printf(" 数据包序列号 = %d. \t", pRecvIcmp->icmp_sequence);
printf(" 延时大小: %d ms", nTick - pRecvIcmp->icmp_timestamp);
printf(" \n");

s_array->Insert(addr);

WSACleanup();
closesocket(sRaw);

return TRUE;
}