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C++如何實(shí)現(xiàn)DNS域名解析

來源：本站原創(chuàng)|時(shí)間：2020-01-10|欄目：C語言|點(diǎn)擊： 次

一、概述

現(xiàn)在來搞定DNS域名解析，其實(shí)這是前面一篇文章C++實(shí)現(xiàn)Ping里面的遺留問題，要干的活是ping的過程中畫紅線的部分：

cmd下域名解析的命令是nslookup，比如“nslookup www.baidu.com”的結(jié)果如下：

其中，Address返回的就是www.baidu.com對應(yīng)的IP地址，這個可能有多個

Alias指別名，也就是說www.baidu.com是www.a.shifen.com的別名，而www.a.shifen.com則是www.baidu.com的規(guī)范名(Canonical Name，CName)，具體參考RFC1035 3.2.2 & wikipedia

二、實(shí)現(xiàn)結(jié)果預(yù)覽

先看一下最終搞成了什么樣子

輸入：域名字符串

輸出：IP列表、CName列表、DNS查詢所用時(shí)間

三、相關(guān)技術(shù)

3.1、UDP or TCP ? (RFC1035 4.2)

UDP：DNS查詢和回復(fù)采用低開銷高性能的UDP，端口號為53。

TCP：輔助DNS服務(wù)器從主DNS服務(wù)器拉取最新數(shù)據(jù)時(shí)，采用可靠的TCP傳輸，端口號也為53。

我們這里做DNS查詢采用UDP，53端口。

3.2、DNS查詢/回復(fù)包頭部解析 (RFC1035 4.1.1)

重點(diǎn)介紹一下我們關(guān)心的部分：

ID(16bits)：標(biāo)識符，一般填入本進(jìn)程的標(biāo)識符

QR(1bits)：標(biāo)志位，查詢包為0，回復(fù)包為1

Opcode(4bits)：查詢的種類，標(biāo)準(zhǔn)查詢?yōu)?

QDCOUNT(16bits)：DNS查詢/回復(fù)包數(shù)據(jù)部分Question字段的個數(shù)

ANCOUNT(16bits)：DNS查詢/回復(fù)包數(shù)據(jù)部分Answer字段的個數(shù)

3.2、DNS查詢/回復(fù)包數(shù)據(jù)部分解析 (RFC1035 4.1.2 & 4.1.3)

查詢/回復(fù)包的數(shù)據(jù)部分依次為QDCOUNT個Question字段、ANCOUNT個Answer字段....

對于任意字段，其格式如下：

Name(不定長)：域名，這部分的格式比較復(fù)雜，后面單獨(dú)說。

TYPE(16bits)：查詢類型/回復(fù)包RDATA類型，比如TYPE=1表示主機(jī)IP地址、TYPE=5表示CNAME，詳見RFC1035 3.2.2

CLASS(16bits)：類，一般情況下CLASS=1表示Internet，詳見RFC1035 3.2.4

TTL(32bits，僅回復(fù)包)：生存時(shí)間

RDLENGTH(16bits，僅回復(fù)包)：RDATA部分的字節(jié)數(shù)

RDATA(不定長，僅回復(fù)包)：資源數(shù)據(jù)，具體格式取決于TYPE和CLASS，比如TYPE=1、CLASS=1時(shí)，RDATA為四個字節(jié)的IP地址

3.3、Name解析&消息壓縮

3.3.1、一般格式 (RFC1035 4.1.2)

標(biāo)簽內(nèi)容長度(1個字節(jié)) + 標(biāo)簽內(nèi)容，以標(biāo)簽內(nèi)容長度0作為Name的結(jié)束符，例如：

3.3.2、消息壓縮格式 (RFC1035 4.1.4)

如果標(biāo)簽內(nèi)容長度的二進(jìn)制前兩位是11，則表示消息壓縮。

此時(shí)，標(biāo)簽內(nèi)容長度1個字節(jié)+后面的1個字節(jié)一共16位，后14位表示相對DNS包起始地址的偏移(Byte)，例如：

上述例子中，DNS包起始地址為0x0000，c0 13的二進(jìn)制為11000000 00010003，即跳轉(zhuǎn)偏移為0x13個字節(jié)，對應(yīng)的數(shù)據(jù)為03 63 6f 6d 00。

RFC1035中規(guī)定，支持的消息壓縮規(guī)則為：

①以內(nèi)容長度0結(jié)尾的標(biāo)簽序列

②偏移指針

③標(biāo)簽序列+偏移指針

也就是說，Name的消息壓縮要求偏移指針必須在Name的尾部，且不支持同一級存在多個偏移指針(偏移指針序列)，

但Name的消息壓縮支持嵌套的偏移指針，即指針指向的偏移位置仍然是以偏移指針結(jié)尾的數(shù)據(jù)

四、代碼實(shí)現(xiàn)

#pragma once

//這里需要導(dǎo)入庫 Ws2_32.lib，在不同的IDE下可能不太一樣
//#pragma comment(lib, "Ws2_32.lib")

#include <windows.h>
#include <string>
#include <vector>

#define MAX_DOMAINNAME_LEN 255
#define DNS_PORT   53
#define DNS_TYPE_SIZE  2
#define DNS_CLASS_SIZE  2
#define DNS_TTL_SIZE  4
#define DNS_DATALEN_SIZE 2
#define DNS_TYPE_A   0x0001 //1 a host address
#define DNS_TYPE_CNAME  0x0005 //5 the canonical name for an alias
#define DNS_PACKET_MAX_SIZE (sizeof(DNSHeader) + MAX_DOMAINNAME_LEN + DNS_TYPE_SIZE + DNS_CLASS_SIZE)

struct DNSHeader
{
 USHORT usTransID; //標(biāo)識符
 USHORT usFlags; //各種標(biāo)志位
 USHORT usQuestionCount; //Question字段個數(shù) 
 USHORT usAnswerCount; //Answer字段個數(shù)
 USHORT usAuthorityCount; //Authority字段個數(shù)
 USHORT usAdditionalCount; //Additional字段個數(shù)
};

class CDNSLookup
{
public:
 CDNSLookup();
 ~CDNSLookup();

 BOOL DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList = NULL, std::vector<std::string> *pvecstrCNameList = NULL, ULONG ulTimeout = 1000, ULONG *pulTimeSpent = NULL);
 BOOL DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<std::string> *pvecstrIPList = NULL, std::vector<std::string> *pvecstrCNameList = NULL, ULONG ulTimeout = 1000, ULONG *pulTimeSpent = NULL);

private:
 BOOL Init();
 BOOL UnInit();
 BOOL DNSLookupCore(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent);
 BOOL SendDNSRequest(sockaddr_in sockAddrDNSServer, char *szDomainName);
 BOOL RecvDNSResponse(sockaddr_in sockAddrDNSServer, ULONG ulTimeout, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG *pulTimeSpent);
 BOOL EncodeDotStr(char *szDotStr, char *szEncodedStr, USHORT nEncodedStrSize);
 BOOL DecodeDotStr(char *szEncodedStr, USHORT *pusEncodedStrLen, char *szDotStr, USHORT nDotStrSize, char *szPacketStartPos = NULL);
 ULONG GetTickCountCalibrate();

private:
 BOOL m_bIsInitOK;
 SOCKET m_sock;
 WSAEVENT m_event;
 USHORT m_usCurrentProcID;
 char *m_szDNSPacket;
};
 [DNSLookup.h]

 

#include "DNSLookup.h"
#include <stdio.h>
#include <string.h>

CDNSLookup::CDNSLookup() : 
 m_bIsInitOK(FALSE), 
 m_sock(INVALID_SOCKET),
 m_szDNSPacket(NULL)
{
 m_bIsInitOK = Init();
}

CDNSLookup::~CDNSLookup()
{
 UnInit();
}

BOOL CDNSLookup::DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent)
{
 return DNSLookupCore(ulDNSServerIP, szDomainName, pveculIPList, pvecstrCNameList, ulTimeout, pulTimeSpent);
}

BOOL CDNSLookup::DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<std::string> *pvecstrIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent)
{
 std::vector<ULONG> *pveculIPList = NULL;
 if (pvecstrIPList != NULL)
 {
  std::vector<ULONG> veculIPList;
  pveculIPList = &veculIPList;
 }

 BOOL bRet = DNSLookupCore(ulDNSServerIP, szDomainName, pveculIPList, pvecstrCNameList, ulTimeout, pulTimeSpent);

 if (bRet)
 {
  pvecstrIPList->clear();
  char szIP[16] = {'\0'};
  for (std::vector<ULONG>::iterator iter = pveculIPList->begin(); iter != pveculIPList->end(); ++iter)
  {
   BYTE *pbyIPSegment = (BYTE*)(&(*iter));
   //sprintf_s(szIP, 16, "%d.%d.%d.%d", pbyIPSegment[0], pbyIPSegment[1], pbyIPSegment[2], pbyIPSegment[3]);
   sprintf(szIP, "%d.%d.%d.%d", pbyIPSegment[0], pbyIPSegment[1], pbyIPSegment[2], pbyIPSegment[3]);
   pvecstrIPList->push_back(szIP);
  }
 }

 return bRet;
}


BOOL CDNSLookup::Init()
{
 WSADATA wsaData;
 if (WSAStartup(MAKEWORD(2, 2), &wsaData) == SOCKET_ERROR)
 {
  return FALSE;
 }
 
 if ((m_sock = socket(AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET)
 {
  return FALSE;
 }

 m_event = WSACreateEvent();
 WSAEventSelect(m_sock, m_event, FD_READ);

 m_szDNSPacket = new (std::nothrow) char[DNS_PACKET_MAX_SIZE];
 if (m_szDNSPacket == NULL)
 {
  return FALSE;
 }

 m_usCurrentProcID = (USHORT)GetCurrentProcessId();

 return TRUE;
}

BOOL CDNSLookup::UnInit()
{
 WSACleanup();

 if (m_szDNSPacket != NULL)
 {
  delete [] m_szDNSPacket;
 }

 return TRUE;
}

BOOL CDNSLookup::DNSLookupCore(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent)
{
 if (m_bIsInitOK == FALSE || szDomainName == NULL)
 {
  return FALSE;
 }

 //配置SOCKET
 sockaddr_in sockAddrDNSServer; 
 sockAddrDNSServer.sin_family = AF_INET; 
 sockAddrDNSServer.sin_addr.s_addr = ulDNSServerIP;
 sockAddrDNSServer.sin_port = htons( DNS_PORT );

 //DNS查詢與解析
 if (!SendDNSRequest(sockAddrDNSServer, szDomainName)
  || !RecvDNSResponse(sockAddrDNSServer, ulTimeout, pveculIPList, pvecstrCNameList, pulTimeSpent))
 {
  return FALSE;
 }

 return TRUE;
}

BOOL CDNSLookup::SendDNSRequest(sockaddr_in sockAddrDNSServer, char *szDomainName)
{
 char *pWriteDNSPacket = m_szDNSPacket;
 memset(pWriteDNSPacket, 0, DNS_PACKET_MAX_SIZE); 

 //填充DNS查詢報(bào)文頭部
 DNSHeader *pDNSHeader = (DNSHeader*)pWriteDNSPacket;
 pDNSHeader->usTransID = m_usCurrentProcID;
 pDNSHeader->usFlags = htons(0x0100);
 pDNSHeader->usQuestionCount = htons(0x0001);
 pDNSHeader->usAnswerCount = 0x0000;
 pDNSHeader->usAuthorityCount = 0x0000;
 pDNSHeader->usAdditionalCount = 0x0000;

 //設(shè)置DNS查詢報(bào)文內(nèi)容
 USHORT usQType = htons(0x0001);
 USHORT usQClass = htons(0x0001);
 USHORT nDomainNameLen = strlen(szDomainName);
 char *szEncodedDomainName = (char *)malloc(nDomainNameLen + 2);
 if (szEncodedDomainName == NULL)
 {
  return FALSE;
 }
 if (!EncodeDotStr(szDomainName, szEncodedDomainName, nDomainNameLen + 2))
 {
  return FALSE;
 }

 //填充DNS查詢報(bào)文內(nèi)容
 USHORT nEncodedDomainNameLen = strlen(szEncodedDomainName) + 1;
 memcpy(pWriteDNSPacket += sizeof(DNSHeader), szEncodedDomainName, nEncodedDomainNameLen);
 memcpy(pWriteDNSPacket += nEncodedDomainNameLen, (char*)(&usQType), DNS_TYPE_SIZE);
 memcpy(pWriteDNSPacket += DNS_TYPE_SIZE, (char*)(&usQClass), DNS_CLASS_SIZE);
 free (szEncodedDomainName);

 //發(fā)送DNS查詢報(bào)文
 USHORT nDNSPacketSize = sizeof(DNSHeader) + nEncodedDomainNameLen + DNS_TYPE_SIZE + DNS_CLASS_SIZE;
 if (sendto(m_sock, m_szDNSPacket, nDNSPacketSize, 0, (sockaddr*)&sockAddrDNSServer, sizeof(sockAddrDNSServer)) == SOCKET_ERROR)
 {
  return FALSE;
 }

 return TRUE;
}

BOOL CDNSLookup::RecvDNSResponse(sockaddr_in sockAddrDNSServer, ULONG ulTimeout, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG *pulTimeSpent)
{
 ULONG ulSendTimestamp = GetTickCountCalibrate();

 if (pveculIPList != NULL)
 {
  pveculIPList->clear();
 }
 if (pvecstrCNameList != NULL)
 {
  pvecstrCNameList->clear();
 }

 char recvbuf[1024] = {'\0'};
 char szDotName[128] = {'\0'};
 USHORT nEncodedNameLen = 0;

 while (TRUE)
 {
  if (WSAWaitForMultipleEvents(1, &m_event, FALSE, 100, FALSE) != WSA_WAIT_TIMEOUT)
  {
   WSANETWORKEVENTS netEvent;
   WSAEnumNetworkEvents(m_sock, m_event, &netEvent);

   if (netEvent.lNetworkEvents & FD_READ)
   {
    ULONG ulRecvTimestamp = GetTickCountCalibrate();
    int nSockaddrDestSize = sizeof(sockAddrDNSServer);

    //接收響應(yīng)報(bào)文
    if (recvfrom(m_sock, recvbuf, 1024, 0, (struct sockaddr*)&sockAddrDNSServer, &nSockaddrDestSize) != SOCKET_ERROR)
    {
     DNSHeader *pDNSHeader = (DNSHeader*)recvbuf;
     USHORT usQuestionCount = 0;
     USHORT usAnswerCount = 0;

     if (pDNSHeader->usTransID == m_usCurrentProcID
      && (ntohs(pDNSHeader->usFlags) & 0xfb7f) == 0x8100 //RFC1035 4.1.1(Header section format)
      && (usQuestionCount = ntohs(pDNSHeader->usQuestionCount)) >= 0
      && (usAnswerCount = ntohs(pDNSHeader->usAnswerCount)) > 0)
     {
      char *pDNSData = recvbuf + sizeof(DNSHeader);

      //解析Question字段
      for (int q = 0; q != usQuestionCount; ++q)
      {
       if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName)))
       {
        return FALSE;
       }
       pDNSData += (nEncodedNameLen + DNS_TYPE_SIZE + DNS_CLASS_SIZE);
      }

      //解析Answer字段
      for (int a = 0; a != usAnswerCount; ++a)
      {
       if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName), recvbuf))
       {
        return FALSE;
       }
       pDNSData += nEncodedNameLen;

       USHORT usAnswerType = ntohs(*(USHORT*)(pDNSData));
       USHORT usAnswerClass = ntohs(*(USHORT*)(pDNSData + DNS_TYPE_SIZE));
       ULONG usAnswerTTL = ntohl(*(ULONG*)(pDNSData + DNS_TYPE_SIZE + DNS_CLASS_SIZE));
       USHORT usAnswerDataLen = ntohs(*(USHORT*)(pDNSData + DNS_TYPE_SIZE + DNS_CLASS_SIZE + DNS_TTL_SIZE));
       pDNSData += (DNS_TYPE_SIZE + DNS_CLASS_SIZE + DNS_TTL_SIZE + DNS_DATALEN_SIZE);

       if (usAnswerType == DNS_TYPE_A && pveculIPList != NULL)
       {
        ULONG ulIP = *(ULONG*)(pDNSData);
        pveculIPList->push_back(ulIP);
       }
       else if (usAnswerType == DNS_TYPE_CNAME && pvecstrCNameList != NULL)
       {
        if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName), recvbuf))
        {
         return FALSE;
        }
        pvecstrCNameList->push_back(szDotName);
       }

       pDNSData += (usAnswerDataLen);
      }

      //計(jì)算DNS查詢所用時(shí)間
      if (pulTimeSpent != NULL)
      {
       *pulTimeSpent = ulRecvTimestamp - ulSendTimestamp;
      }

      break;
     }
    }
   }
  }

  //超時(shí)退出
  if (GetTickCountCalibrate() - ulSendTimestamp > ulTimeout)
  {
   *pulTimeSpent = ulTimeout + 1;
   return FALSE;
  }
 }

 return TRUE;
}

/*
 * convert "www.baidu.com" to "\x03www\x05baidu\x03com"
 * 0x0000 03 77 77 77 05 62 61 69 64 75 03 63 6f 6d 00 ff
 */
BOOL CDNSLookup::EncodeDotStr(char *szDotStr, char *szEncodedStr, USHORT nEncodedStrSize)
{
 USHORT nDotStrLen = strlen(szDotStr);

 if (szDotStr == NULL || szEncodedStr == NULL || nEncodedStrSize < nDotStrLen + 2)
 {
  return FALSE;
 }

 char *szDotStrCopy = new char[nDotStrLen + 1];
 //strcpy_s(szDotStrCopy, nDotStrLen + 1, szDotStr);
 strcpy(szDotStrCopy, szDotStr);

 char *pNextToken = NULL;
 //char *pLabel = strtok_s(szDotStrCopy, ".", &pNextToken);
 char *pLabel = strtok(szDotStrCopy, ".");
 USHORT nLabelLen = 0;
 USHORT nEncodedStrLen = 0;
 while (pLabel != NULL)
 {
  if ((nLabelLen = strlen(pLabel)) != 0)
  {
   //sprintf_s(szEncodedStr + nEncodedStrLen, nEncodedStrSize - nEncodedStrLen, "%c%s", nLabelLen, pLabel);
   sprintf(szEncodedStr + nEncodedStrLen, "%c%s", nLabelLen, pLabel);
   nEncodedStrLen += (nLabelLen + 1);
  }
  //pLabel = strtok_s(NULL, ".", &pNextToken);
  pLabel = strtok(NULL, ".");
 }

 delete [] szDotStrCopy;
 
 return TRUE;
}

/*
 * convert "\x03www\x05baidu\x03com\x00" to "www.baidu.com"
 * 0x0000 03 77 77 77 05 62 61 69 64 75 03 63 6f 6d 00 ff
 * convert "\x03www\x05baidu\xc0\x13" to "www.baidu.com"
 * 0x0000 03 77 77 77 05 62 61 69 64 75 c0 13 ff ff ff ff
 * 0x0010 ff ff ff 03 63 6f 6d 00 ff ff ff ff ff ff ff ff
 */
BOOL CDNSLookup::DecodeDotStr(char *szEncodedStr, USHORT *pusEncodedStrLen, char *szDotStr, USHORT nDotStrSize, char *szPacketStartPos)
{
 if (szEncodedStr == NULL || pusEncodedStrLen == NULL || szDotStr == NULL)
 {
  return FALSE;
 }

 char *pDecodePos = szEncodedStr;
 USHORT usPlainStrLen = 0;
 BYTE nLabelDataLen = 0; 
 *pusEncodedStrLen = 0;

 while ((nLabelDataLen = *pDecodePos) != 0x00)
 {
  if ((nLabelDataLen & 0xc0) == 0) //普通格式，LabelDataLen + Label
  {
   if (usPlainStrLen + nLabelDataLen + 1 > nDotStrSize)
   {
    return FALSE;
   }
   memcpy(szDotStr + usPlainStrLen, pDecodePos + 1, nLabelDataLen);
   memcpy(szDotStr + usPlainStrLen + nLabelDataLen, ".", 1);
   pDecodePos += (nLabelDataLen + 1);
   usPlainStrLen += (nLabelDataLen + 1);
   *pusEncodedStrLen += (nLabelDataLen + 1);
  }
  else //消息壓縮格式，11000000 00000000，兩個字節(jié)，前2位為跳轉(zhuǎn)標(biāo)志，后14位為跳轉(zhuǎn)的偏移
  {
   if (szPacketStartPos == NULL)
   {
    return FALSE;
   }
   USHORT usJumpPos = ntohs(*(USHORT*)(pDecodePos)) & 0x3fff;
   USHORT nEncodeStrLen = 0;
   if (!DecodeDotStr(szPacketStartPos + usJumpPos, &nEncodeStrLen, szDotStr + usPlainStrLen, nDotStrSize - usPlainStrLen, szPacketStartPos))
   {
    return FALSE;
   }
   else
   {
    *pusEncodedStrLen += 2;
    return TRUE;
   }
  }
 }

 szDotStr[usPlainStrLen - 1] = '\0';
 *pusEncodedStrLen += 1;

 return TRUE;
}

ULONG CDNSLookup::GetTickCountCalibrate()
{
 static ULONG s_ulFirstCallTick = 0;
 static LONGLONG s_ullFirstCallTickMS = 0;

 SYSTEMTIME systemtime;
 FILETIME filetime;
 GetLocalTime(&systemtime); 
 SystemTimeToFileTime(&systemtime, &filetime);
 LARGE_INTEGER liCurrentTime;
 liCurrentTime.HighPart = filetime.dwHighDateTime;
 liCurrentTime.LowPart = filetime.dwLowDateTime;
 LONGLONG llCurrentTimeMS = liCurrentTime.QuadPart / 10000;

 if (s_ulFirstCallTick == 0)
 {
  s_ulFirstCallTick = GetTickCount();
 }
 if (s_ullFirstCallTickMS == 0)
 {
  s_ullFirstCallTickMS = llCurrentTimeMS;
 }

 return s_ulFirstCallTick + (ULONG)(llCurrentTimeMS - s_ullFirstCallTickMS);
}
 [DNSLookup.cpp]

 

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

int main(void)
{
 char szDomainName[] = "www.baidu.com";
 std::vector<ULONG> veculIPList;
 std::vector<std::string> vecstrIPList;
 std::vector<std::string> vecCNameList;
 ULONG ulTimeSpent = 0;
 CDNSLookup dnslookup;
 BOOL bRet = dnslookup.DNSLookup(inet_addr("114.114.114.114"), szDomainName, &vecstrIPList, &vecCNameList, 1000, &ulTimeSpent);

 printf("DNSLookup result (%s):\n", szDomainName);
 if (!bRet)
 {
  printf("timeout!\n");
  return -1;
 }

 for (int i = 0; i != veculIPList.size(); ++i)
 {
  printf("IP%d(ULONG) = %u\n", i + 1, veculIPList[i]);
 }
 for (int i = 0; i != vecstrIPList.size(); ++i)
 {
  printf("IP%d(string) = %s\n", i + 1, vecstrIPList[i].c_str());
 }
 for (int i = 0; i != vecCNameList.size(); ++i)
 {
  printf("CName%d = %s\n", i + 1, vecCNameList[i].c_str());
 }
 printf("time spent = %ums\n", ulTimeSpent);
 
 return 0;
}

以上就是C++實(shí)現(xiàn)DNS域名解析的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助。

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