C++实现DNS域名解析

一、概述

现在来搞定DNS域名解析，其实这是前面一篇文章C++实现Ping里面的遗留问题，要干的活是ping的过程中画红线的部分：

cmd下域名解析的命令是nslookup，比如“nslookup www.baidu.com”的结果如下：

其中，Address返回的就是www.baidu.com对应的IP地址，这个可能有多个

Alias指别名，也就是说www.baidu.com是www.a.shifen.com的别名，而www.a.shifen.com则是www.baidu.com的规范名(Canonical Name，CName)，具体参考RFC1035 3.2.2 & wikipedia

[转载请保留本文地址：http://www.cnblogs.com/goagent/p/4101729.html]

二、实现结果预览

先看一下最终搞成了什么样子

输入：域名字符串

输出：IP列表、CName列表、DNS查询所用时间

[转载请保留本文地址：http://www.cnblogs.com/goagent/p/4101729.html]

三、相关技术

3.1、UDP or TCP ? (RFC1035 4.2)

UDP：DNS查询和回复采用低开销高性能的UDP，端口号为53。

TCP：辅助DNS服务器从主DNS服务器拉取最新数据时，采用可靠的TCP传输，端口号也为53。

我们这里做DNS查询采用UDP，53端口。

3.2、DNS查询/回复包头部解析 (RFC1035 4.1.1)

重点介绍一下我们关心的部分：

ID(16bits)：标识符，一般填入本进程的标识符

QR(1bits)：标志位，查询包为0，回复包为1

Opcode(4bits)：查询的种类，标准查询为0

QDCOUNT(16bits)：DNS查询/回复包数据部分Question字段的个数

ANCOUNT(16bits)：DNS查询/回复包数据部分Answer字段的个数

3.2、DNS查询/回复包数据部分解析 (RFC1035 4.1.2 & 4.1.3)

查询/回复包的数据部分依次为QDCOUNT个Question字段、ANCOUNT个Answer字段....

对于任意字段，其格式如下：

Name(不定长)：域名，这部分的格式比较复杂，后面单独说。

TYPE(16bits)：查询类型/回复包RDATA类型，比如TYPE=1表示主机IP地址、TYPE=5表示CNAME，详见RFC1035 3.2.2

CLASS(16bits)：类，一般情况下CLASS=1表示Internet，详见RFC1035 3.2.4

TTL(32bits，仅回复包)：生存时间

RDLENGTH(16bits，仅回复包)：RDATA部分的字节数

RDATA(不定长，仅回复包)：资源数据，具体格式取决于TYPE和CLASS，比如TYPE=1、CLASS=1时，RDATA为四个字节的IP地址

3.3、Name解析&消息压缩

3.3.1、一般格式 (RFC1035 4.1.2)

标签内容长度(1个字节) + 标签内容，以标签内容长度0作为Name的结束符，例如：

3.3.2、消息压缩格式 (RFC1035 4.1.4)

如果标签内容长度的二进制前两位是11，则表示消息压缩。

此时，标签内容长度1个字节+后面的1个字节一共16位，后14位表示相对DNS包起始地址的偏移(Byte)，例如：

上述例子中，DNS包起始地址为0x0000，c0 13的二进制为11000000 00010003，即跳转偏移为0x13个字节，对应的数据为03 63 6f 6d 00。

RFC1035中规定，支持的消息压缩规则为：

①以内容长度0结尾的标签序列

②偏移指针

③标签序列+偏移指针

也就是说，Name的消息压缩要求偏移指针必须在Name的尾部，且不支持同一级存在多个偏移指针(偏移指针序列)，

但Name的消息压缩支持嵌套的偏移指针，即指针指向的偏移位置仍然是以偏移指针结尾的数据

[转载请保留本文地址：http://www.cnblogs.com/goagent/p/4101729.html]

四、代码实现

 1 #pragma once
 2 
 3 //这里需要导入库 Ws2_32.lib，在不同的IDE下可能不太一样
 4 //#pragma comment(lib, "Ws2_32.lib")
 5 
 6 #include <windows.h>
 7 #include <string>
 8 #include <vector>
 9 
10 #define MAX_DOMAINNAME_LEN  255
11 #define DNS_PORT            53
12 #define DNS_TYPE_SIZE       2
13 #define DNS_CLASS_SIZE      2
14 #define DNS_TTL_SIZE        4
15 #define DNS_DATALEN_SIZE    2
16 #define DNS_TYPE_A          0x0001 //1 a host address
17 #define DNS_TYPE_CNAME      0x0005 //5 the canonical name for an alias
18 #define DNS_PACKET_MAX_SIZE (sizeof(DNSHeader) + MAX_DOMAINNAME_LEN + DNS_TYPE_SIZE + DNS_CLASS_SIZE)
19 
20 struct DNSHeader
21 {
22     USHORT usTransID; //标识符
23     USHORT usFlags; //各种标志位
24     USHORT usQuestionCount; //Question字段个数 
25     USHORT usAnswerCount; //Answer字段个数
26     USHORT usAuthorityCount; //Authority字段个数
27     USHORT usAdditionalCount; //Additional字段个数
28 };
29 
30 class CDNSLookup
31 {
32 public:
33     CDNSLookup();
34     ~CDNSLookup();
35 
36     BOOL DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList = NULL, std::vector<std::string> *pvecstrCNameList = NULL, ULONG ulTimeout = 1000, ULONG *pulTimeSpent = NULL);
37     BOOL DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<std::string> *pvecstrIPList = NULL, std::vector<std::string> *pvecstrCNameList = NULL, ULONG ulTimeout = 1000, ULONG *pulTimeSpent = NULL);
38 
39 private:
40     BOOL Init();
41     BOOL UnInit();
42     BOOL DNSLookupCore(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent);
43     BOOL SendDNSRequest(sockaddr_in sockAddrDNSServer, char *szDomainName);
44     BOOL RecvDNSResponse(sockaddr_in sockAddrDNSServer, ULONG ulTimeout, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG *pulTimeSpent);
45     BOOL EncodeDotStr(char *szDotStr, char *szEncodedStr, USHORT nEncodedStrSize);
46     BOOL DecodeDotStr(char *szEncodedStr, USHORT *pusEncodedStrLen, char *szDotStr, USHORT nDotStrSize, char *szPacketStartPos = NULL);
47     ULONG GetTickCountCalibrate();
48 
49 private:
50     BOOL m_bIsInitOK;
51     SOCKET m_sock;
52     WSAEVENT m_event;
53     USHORT m_usCurrentProcID;
54     char *m_szDNSPacket;
55 };

View Code [DNSLookup.h]

  1 #include "DNSLookup.h"
  2 #include <stdio.h>
  3 #include <string.h>
  4 
  5 CDNSLookup::CDNSLookup() : 
  6     m_bIsInitOK(FALSE), 
  7     m_sock(INVALID_SOCKET),
  8     m_szDNSPacket(NULL)
  9 {
 10     m_bIsInitOK = Init();
 11 }
 12 
 13 CDNSLookup::~CDNSLookup()
 14 {
 15     UnInit();
 16 }
 17 
 18 BOOL CDNSLookup::DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent)
 19 {
 20     return DNSLookupCore(ulDNSServerIP, szDomainName, pveculIPList, pvecstrCNameList, ulTimeout, pulTimeSpent);
 21 }
 22 
 23 BOOL CDNSLookup::DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<std::string> *pvecstrIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent)
 24 {
 25     std::vector<ULONG> *pveculIPList = NULL;
 26     if (pvecstrIPList != NULL)
 27     {
 28         std::vector<ULONG> veculIPList;
 29         pveculIPList = &veculIPList;
 30     }
 31 
 32     BOOL bRet = DNSLookupCore(ulDNSServerIP, szDomainName, pveculIPList, pvecstrCNameList, ulTimeout, pulTimeSpent);
 33 
 34     if (bRet)
 35     {
 36         pvecstrIPList->clear();
 37         char szIP[16] = {''};
 38         for (std::vector<ULONG>::iterator iter = pveculIPList->begin(); iter != pveculIPList->end(); ++iter)
 39         {
 40             BYTE *pbyIPSegment = (BYTE*)(&(*iter));
 41             //sprintf_s(szIP, 16, "%d.%d.%d.%d", pbyIPSegment[0], pbyIPSegment[1], pbyIPSegment[2], pbyIPSegment[3]);
 42             sprintf(szIP, "%d.%d.%d.%d", pbyIPSegment[0], pbyIPSegment[1], pbyIPSegment[2], pbyIPSegment[3]);
 43             pvecstrIPList->push_back(szIP);
 44         }
 45     }
 46 
 47     return bRet;
 48 }
 49 
 50 
 51 BOOL CDNSLookup::Init()
 52 {
 53     WSADATA wsaData;
 54     if (WSAStartup(MAKEWORD(2, 2), &wsaData) == SOCKET_ERROR)
 55     {
 56         return FALSE;
 57     }
 58     
 59     if ((m_sock = socket(AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET)
 60     {
 61         return FALSE;
 62     }
 63 
 64     m_event = WSACreateEvent();
 65     WSAEventSelect(m_sock, m_event, FD_READ);
 66 
 67     m_szDNSPacket = new (std::nothrow) char[DNS_PACKET_MAX_SIZE];
 68     if (m_szDNSPacket == NULL)
 69     {
 70         return FALSE;
 71     }
 72 
 73     m_usCurrentProcID = (USHORT)GetCurrentProcessId();
 74 
 75     return TRUE;
 76 }
 77 
 78 BOOL CDNSLookup::UnInit()
 79 {
 80     WSACleanup();
 81 
 82     if (m_szDNSPacket != NULL)
 83     {
 84         delete [] m_szDNSPacket;
 85     }
 86 
 87     return TRUE;
 88 }
 89 
 90 BOOL CDNSLookup::DNSLookupCore(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent)
 91 {
 92     if (m_bIsInitOK == FALSE || szDomainName == NULL)
 93     {
 94         return FALSE;
 95     }
 96 
 97     //配置SOCKET
 98     sockaddr_in sockAddrDNSServer; 
 99     sockAddrDNSServer.sin_family = AF_INET; 
100     sockAddrDNSServer.sin_addr.s_addr = ulDNSServerIP;
101     sockAddrDNSServer.sin_port = htons( DNS_PORT );
102 
103     //DNS查询与解析
104     if (!SendDNSRequest(sockAddrDNSServer, szDomainName)
105         || !RecvDNSResponse(sockAddrDNSServer, ulTimeout, pveculIPList, pvecstrCNameList, pulTimeSpent))
106     {
107         return FALSE;
108     }
109 
110     return TRUE;
111 }
112 
113 BOOL CDNSLookup::SendDNSRequest(sockaddr_in sockAddrDNSServer, char *szDomainName)
114 {
115     char *pWriteDNSPacket = m_szDNSPacket;
116     memset(pWriteDNSPacket, 0, DNS_PACKET_MAX_SIZE);    
117 
118     //填充DNS查询报文头部
119     DNSHeader *pDNSHeader = (DNSHeader*)pWriteDNSPacket;
120     pDNSHeader->usTransID = m_usCurrentProcID;
121     pDNSHeader->usFlags = htons(0x0100);
122     pDNSHeader->usQuestionCount = htons(0x0001);
123     pDNSHeader->usAnswerCount = 0x0000;
124     pDNSHeader->usAuthorityCount = 0x0000;
125     pDNSHeader->usAdditionalCount = 0x0000;
126 
127     //设置DNS查询报文内容
128     USHORT usQType = htons(0x0001);
129     USHORT usQClass = htons(0x0001);
130     USHORT nDomainNameLen = strlen(szDomainName);
131     char *szEncodedDomainName = (char *)malloc(nDomainNameLen + 2);
132     if (szEncodedDomainName == NULL)
133     {
134         return FALSE;
135     }
136     if (!EncodeDotStr(szDomainName, szEncodedDomainName, nDomainNameLen + 2))
137     {
138         return FALSE;
139     }
140 
141     //填充DNS查询报文内容
142     USHORT nEncodedDomainNameLen = strlen(szEncodedDomainName) + 1;
143     memcpy(pWriteDNSPacket += sizeof(DNSHeader), szEncodedDomainName, nEncodedDomainNameLen);
144     memcpy(pWriteDNSPacket += nEncodedDomainNameLen, (char*)(&usQType), DNS_TYPE_SIZE);
145     memcpy(pWriteDNSPacket += DNS_TYPE_SIZE, (char*)(&usQClass), DNS_CLASS_SIZE);
146     free (szEncodedDomainName);
147 
148     //发送DNS查询报文
149     USHORT nDNSPacketSize = sizeof(DNSHeader) + nEncodedDomainNameLen + DNS_TYPE_SIZE + DNS_CLASS_SIZE;
150     if (sendto(m_sock, m_szDNSPacket, nDNSPacketSize, 0, (sockaddr*)&sockAddrDNSServer, sizeof(sockAddrDNSServer)) == SOCKET_ERROR)
151     {
152         return FALSE;
153     }
154 
155     return TRUE;
156 }
157 
158 BOOL CDNSLookup::RecvDNSResponse(sockaddr_in sockAddrDNSServer, ULONG ulTimeout, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG *pulTimeSpent)
159 {
160     ULONG ulSendTimestamp = GetTickCountCalibrate();
161 
162     if (pveculIPList != NULL)
163     {
164         pveculIPList->clear();
165     }
166     if (pvecstrCNameList != NULL)
167     {
168         pvecstrCNameList->clear();
169     }
170 
171     char recvbuf[1024] = {''};
172     char szDotName[128] = {''};
173     USHORT nEncodedNameLen = 0;
174 
175     while (TRUE)
176     {
177         if (WSAWaitForMultipleEvents(1, &m_event, FALSE, 100, FALSE) != WSA_WAIT_TIMEOUT)
178         {
179             WSANETWORKEVENTS netEvent;
180             WSAEnumNetworkEvents(m_sock, m_event, &netEvent);
181 
182             if (netEvent.lNetworkEvents & FD_READ)
183             {
184                 ULONG ulRecvTimestamp = GetTickCountCalibrate();
185                 int nSockaddrDestSize = sizeof(sockAddrDNSServer);
186 
187                 //接收响应报文
188                 if (recvfrom(m_sock, recvbuf, 1024, 0, (struct sockaddr*)&sockAddrDNSServer, &nSockaddrDestSize) != SOCKET_ERROR)
189                 {
190                     DNSHeader *pDNSHeader = (DNSHeader*)recvbuf;
191                     USHORT usQuestionCount = 0;
192                     USHORT usAnswerCount = 0;
193 
194                     if (pDNSHeader->usTransID == m_usCurrentProcID
195                         && (ntohs(pDNSHeader->usFlags) & 0xfb7f) == 0x8100 //RFC1035 4.1.1(Header section format)
196                         && (usQuestionCount = ntohs(pDNSHeader->usQuestionCount)) >= 0
197                         && (usAnswerCount = ntohs(pDNSHeader->usAnswerCount)) > 0)
198                     {
199                         char *pDNSData = recvbuf + sizeof(DNSHeader);
200 
201                         //解析Question字段
202                         for (int q = 0; q != usQuestionCount; ++q)
203                         {
204                             if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName)))
205                             {
206                                 return FALSE;
207                             }
208                             pDNSData += (nEncodedNameLen + DNS_TYPE_SIZE + DNS_CLASS_SIZE);
209                         }
210 
211                         //解析Answer字段
212                         for (int a = 0; a != usAnswerCount; ++a)
213                         {
214                             if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName), recvbuf))
215                             {
216                                 return FALSE;
217                             }
218                             pDNSData += nEncodedNameLen;
219 
220                             USHORT usAnswerType = ntohs(*(USHORT*)(pDNSData));
221                             USHORT usAnswerClass = ntohs(*(USHORT*)(pDNSData + DNS_TYPE_SIZE));
222                             ULONG usAnswerTTL = ntohl(*(ULONG*)(pDNSData + DNS_TYPE_SIZE + DNS_CLASS_SIZE));
223                             USHORT usAnswerDataLen = ntohs(*(USHORT*)(pDNSData + DNS_TYPE_SIZE + DNS_CLASS_SIZE + DNS_TTL_SIZE));
224                             pDNSData += (DNS_TYPE_SIZE + DNS_CLASS_SIZE + DNS_TTL_SIZE + DNS_DATALEN_SIZE);
225 
226                             if (usAnswerType == DNS_TYPE_A && pveculIPList != NULL)
227                             {
228                                 ULONG ulIP = *(ULONG*)(pDNSData);
229                                 pveculIPList->push_back(ulIP);
230                             }
231                             else if (usAnswerType == DNS_TYPE_CNAME && pvecstrCNameList != NULL)
232                             {
233                                 if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName), recvbuf))
234                                 {
235                                     return FALSE;
236                                 }
237                                 pvecstrCNameList->push_back(szDotName);
238                             }
239 
240                             pDNSData += (usAnswerDataLen);
241                         }
242 
243                         //计算DNS查询所用时间
244                         if (pulTimeSpent != NULL)
245                         {
246                             *pulTimeSpent = ulRecvTimestamp - ulSendTimestamp;
247                         }
248 
249                         break;
250                     }
251                 }
252             }
253         }
254 
255         //超时退出
256         if (GetTickCountCalibrate() - ulSendTimestamp > ulTimeout)
257         {
258             *pulTimeSpent = ulTimeout + 1;
259             return FALSE;
260         }
261     }
262 
263     return TRUE;
264 }
265 
266 /*
267  * convert "www.baidu.com" to "x03wwwx05baidux03com"
268  * 0x0000 03 77 77 77 05 62 61 69 64 75 03 63 6f 6d 00 ff
269  */
270 BOOL CDNSLookup::EncodeDotStr(char *szDotStr, char *szEncodedStr, USHORT nEncodedStrSize)
271 {
272     USHORT nDotStrLen = strlen(szDotStr);
273 
274     if (szDotStr == NULL || szEncodedStr == NULL || nEncodedStrSize < nDotStrLen + 2)
275     {
276         return FALSE;
277     }
278 
279     char *szDotStrCopy = new char[nDotStrLen + 1];
280     //strcpy_s(szDotStrCopy, nDotStrLen + 1, szDotStr);
281     strcpy(szDotStrCopy, szDotStr);
282 
283     char *pNextToken = NULL;
284     //char *pLabel = strtok_s(szDotStrCopy, ".", &pNextToken);
285     char *pLabel = strtok(szDotStrCopy, ".");
286     USHORT nLabelLen = 0;
287     USHORT nEncodedStrLen = 0;
288     while (pLabel != NULL)
289     {
290         if ((nLabelLen = strlen(pLabel)) != 0)
291         {
292             //sprintf_s(szEncodedStr + nEncodedStrLen, nEncodedStrSize - nEncodedStrLen, "%c%s", nLabelLen, pLabel);
293             sprintf(szEncodedStr + nEncodedStrLen, "%c%s", nLabelLen, pLabel);
294             nEncodedStrLen += (nLabelLen + 1);
295         }
296         //pLabel = strtok_s(NULL, ".", &pNextToken);
297         pLabel = strtok(NULL, ".");
298     }
299 
300     delete [] szDotStrCopy;
301     
302     return TRUE;
303 }
304 
305 /*
306  * convert "x03wwwx05baidux03comx00" to "www.baidu.com"
307  * 0x0000 03 77 77 77 05 62 61 69 64 75 03 63 6f 6d 00 ff
308  * convert "x03wwwx05baiduxc0x13" to "www.baidu.com"
309  * 0x0000 03 77 77 77 05 62 61 69 64 75 c0 13 ff ff ff ff
310  * 0x0010 ff ff ff 03 63 6f 6d 00 ff ff ff ff ff ff ff ff
311  */
312 BOOL CDNSLookup::DecodeDotStr(char *szEncodedStr, USHORT *pusEncodedStrLen, char *szDotStr, USHORT nDotStrSize, char *szPacketStartPos)
313 {
314     if (szEncodedStr == NULL || pusEncodedStrLen == NULL || szDotStr == NULL)
315     {
316         return FALSE;
317     }
318 
319     char *pDecodePos = szEncodedStr;
320     USHORT usPlainStrLen = 0;
321     BYTE nLabelDataLen = 0;    
322     *pusEncodedStrLen = 0;
323 
324     while ((nLabelDataLen = *pDecodePos) != 0x00)
325     {
326         if ((nLabelDataLen & 0xc0) == 0) //普通格式，LabelDataLen + Label
327         {
328             if (usPlainStrLen + nLabelDataLen + 1 > nDotStrSize)
329             {
330                 return FALSE;
331             }
332             memcpy(szDotStr + usPlainStrLen, pDecodePos + 1, nLabelDataLen);
333             memcpy(szDotStr + usPlainStrLen + nLabelDataLen, ".", 1);
334             pDecodePos += (nLabelDataLen + 1);
335             usPlainStrLen += (nLabelDataLen + 1);
336             *pusEncodedStrLen += (nLabelDataLen + 1);
337         }
338         else //消息压缩格式，11000000 00000000，两个字节，前2位为跳转标志，后14位为跳转的偏移
339         {
340             if (szPacketStartPos == NULL)
341             {
342                 return FALSE;
343             }
344             USHORT usJumpPos = ntohs(*(USHORT*)(pDecodePos)) & 0x3fff;
345             USHORT nEncodeStrLen = 0;
346             if (!DecodeDotStr(szPacketStartPos + usJumpPos, &nEncodeStrLen, szDotStr + usPlainStrLen, nDotStrSize - usPlainStrLen, szPacketStartPos))
347             {
348                 return FALSE;
349             }
350             else
351             {
352                 *pusEncodedStrLen += 2;
353                 return TRUE;
354             }
355         }
356     }
357 
358     szDotStr[usPlainStrLen - 1] = '';
359     *pusEncodedStrLen += 1;
360 
361     return TRUE;
362 }
363 
364 ULONG CDNSLookup::GetTickCountCalibrate()
365 {
366     static ULONG s_ulFirstCallTick = 0;
367     static LONGLONG s_ullFirstCallTickMS = 0;
368 
369     SYSTEMTIME systemtime;
370     FILETIME filetime;
371     GetLocalTime(&systemtime);    
372     SystemTimeToFileTime(&systemtime, &filetime);
373     LARGE_INTEGER liCurrentTime;
374     liCurrentTime.HighPart = filetime.dwHighDateTime;
375     liCurrentTime.LowPart = filetime.dwLowDateTime;
376     LONGLONG llCurrentTimeMS = liCurrentTime.QuadPart / 10000;
377 
378     if (s_ulFirstCallTick == 0)
379     {
380         s_ulFirstCallTick = GetTickCount();
381     }
382     if (s_ullFirstCallTickMS == 0)
383     {
384         s_ullFirstCallTickMS = llCurrentTimeMS;
385     }
386 
387     return s_ulFirstCallTick + (ULONG)(llCurrentTimeMS - s_ullFirstCallTickMS);
388 }

View Code [DNSLookup.cpp]

 1 #include <stdio.h>
 2 #include <windows.h>
 3 #include "DNSLookup.h"
 4 
 5 int main(void)
 6 {
 7     char szDomainName[] = "www.baidu.com";
 8     std::vector<ULONG> veculIPList;
 9     std::vector<std::string> vecstrIPList;
10     std::vector<std::string> vecCNameList;
11     ULONG ulTimeSpent = 0;
12     CDNSLookup dnslookup;
13     BOOL bRet = dnslookup.DNSLookup(inet_addr("114.114.114.114"), szDomainName, &vecstrIPList, &vecCNameList, 1000, &ulTimeSpent);
14 
15     printf("DNSLookup result (%s):
", szDomainName);
16     if (!bRet)
17     {
18         printf("timeout!
");
19         return -1;
20     }
21 
22     for (int i = 0; i != veculIPList.size(); ++i)
23     {
24         printf("IP%d(ULONG) = %u
", i + 1, veculIPList[i]);
25     }
26     for (int i = 0; i != vecstrIPList.size(); ++i)
27     {
28         printf("IP%d(string) = %s
", i + 1, vecstrIPList[i].c_str());
29     }
30     for (int i = 0; i != vecCNameList.size(); ++i)
31     {
32         printf("CName%d = %s
", i + 1, vecCNameList[i].c_str());
33     }
34     printf("time spent = %ums
", ulTimeSpent);
35     
36     return 0;
37 }

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