使用c語言實現域名解析的方法

c語言代碼如下：

#include  
#include  
#include  
typedef enum {false = 0, true = !false}bool; 
typedef struct _DNSHEAD{ //dns 頭部 
USHORT ID; 
USHORT tag; // dns 標志(參數) 
USHORT numQ; // 問題數 
USHORT numA; // 答案數 
USHORT numA1; // 權威答案數 
USHORT numA2; // 附加答案數 
}DnsHead; 
typedef struct _DNSQUERY //dns 查詢結構 
{ 
// char name[64]; 
// //查詢的域名,這是一個大小在0到63之間的字符串； 
USHORT type; 
//查詢類型，大約有20個不同的類型 
USHORT classes; 
//查詢類,通常是A類既查詢IP地址。 
}DnsQuery; 
#pragma comment(lib,"ws2_32.lib") 
// 初始化操作 
bool initWSA(); 
//顯示錯誤 
void displayErrWSA(char *str); 
//創建套接字 
SOCKET CreateSocket(int type); 
//UDP sendto 
int MySendto(SOCKET sockTo, const char FAR * buf,int len,char *addr,USHORT port); 
//TCP 連接 
bool MyConnect(SOCKET s, char *addr,USHORT ); 
// UDP recvfrom 
int MyRecvFrom(SOCKET s, char FAR * buf,int len,char *addr,USHORT port); 
//設置DNS 頭部 
bool SetDNSHead(char *name,char *buf); 
int main(int arg,char *are[]) 
{ 
int Result=0; 
char buf[1024]={0}; 
char addr[16] = "192.168.1.1";// dns 服務器地址 
char *name = 0; //要查詢的域名 
SOCKET sockTo; 
int len; 
DnsHead *DnsH; 
char *getIP; 
//int i; 
if ( !initWSA() )//初始化 
{ 
displayErrWSA("initWSA err!"); 
return 1; 
} 
//創建套接字 
if ( (sockTo = CreateSocket(SOCK_DGRAM)) == 0) 
{ 
displayErrWSA("CreatSocket err!"); 
return 1; 
} 
while (1) 
{ 
if (arg < 2) 
{ 
char temp[1024]={0}; 
printf("\n請輸入要查詢的域名:"); 
scanf("%s",temp); 
if (temp[0] == 'q' ||temp[0] == 'Q') 
{ 
break; 
} 
name = temp; 
} 
else 
{ 
arg = 1; 
name = are[1]; 
} 
//設置dns 頭部 
SetDNSHead(name,buf); 
//發送出去的請求數據長度 
len = sizeof(DnsHead)+sizeof(DnsQuery)+strlen(name)+2; 
// for (int i =0;i<50;i+=2) 
// { 
// printf("x",(UCHAR)buf[i]); 
// printf("x ",(UCHAR)buf[i+1]); 
// } 
//發送DNS 請求 
if ( ( Result =MySendto(sockTo,buf,len,addr,53) ) <= 0) 
{ 
displayErrWSA("sendto err!"); 
continue; 
} 
//接收應答 
if ( (Result =MyRecvFrom(sockTo,buf,1024,addr,53) ) <= 0) 
{ 
displayErrWSA("recvfrom err!"); 
continue; 
} 
//簡單的取得返回的 IP 地址( 收到的最后4字節 ) 
DnsH = (DnsHead *)buf; 
if (DnsH->numA == 0) 
{ 
printf("無法解析 %s 的IP 地址。\n",name); 
continue; 
} 
getIP =(char *)buf +Result - 4; 
printf("%s 的IP地址為: ",name); 
for (Result= 0 ;Result<4 ;Result++) 
{ 
printf("%u.",(UCHAR )getIP[Result]); 
} 
printf("\n"); 
} 
return 0; 
} 
// 初始化操作 
bool initWSA() 
{ 
WORD wVersionRequested; 
WSADATA wsaData; 
int Result; 
wVersionRequested = MAKEWORD( 2, 2 ); 
Result = WSAStartup( wVersionRequested, &wsaData ); 
if(Result != 0 ) 
{ 
return false; 
} 
if( LOBYTE( wsaData.wVersion) != 2 || 
HIBYTE(wsaData.wVersion)!= 2 ) 
{ 
WSACleanup(); 
return false; 
} 
return true; 
} 
SOCKET CreateSocket(int type) 
{ 
SOCKET sock=socket(AF_INET,type,0); 
if (sock == INVALID_SOCKET ) 
{ 
return 0; 
} 
return sock; 
} 
int MySendto(SOCKET sockTo, const char FAR * buf,int len,char *addr,USHORT port) 
{ 
//設置發送數據到的 套接字及地址結構 
SOCKADDR_IN addrTo; 
addrTo.sin_addr.S_un.S_addr=inet_addr(addr); 
addrTo.sin_family=AF_INET; 
addrTo.sin_port=htons(port); 
return sendto( sockTo, buf, len, 0, 
(struct sockaddr *)&addrTo, sizeof(struct sockaddr) ); 
} 
bool MyConnect(SOCKET sockTo, char *addr,USHORT port) 
{ 
int Result; 
//設置連接到的 套接字及地址結構 
SOCKADDR_IN addrTo; 
addrTo.sin_addr.S_un.S_addr=(inet_addr(addr)); 
addrTo.sin_family=AF_INET; 
addrTo.sin_port=htons(port); 
//連接 
Result = connect(sockTo,(struct sockaddr *)&addrTo,sizeof(SOCKADDR_IN)); 
if(SOCKET_ERROR == Result) 
{ 
return false; 
} 
return true; 
} 
int MyRecvFrom(SOCKET s, char FAR * buf,int len,char *addr,USHORT port) 
{ 
//設置發送數據到的 套接字及地址結構 
int addrlen; 
SOCKADDR_IN addrFrom; 
addrFrom.sin_addr.S_un.S_addr=inet_addr(addr); 
addrFrom.sin_family=AF_INET; 
addrFrom.sin_port=htons(port); 
addrlen = sizeof(SOCKADDR_IN); 
return recvfrom( s, buf, len, 0, (SOCKADDR *)&addrFrom, &addrlen); 
} 
int ChName(char *fname,char *tname);//域名轉化 
bool SetDNSHead(char *name,char *buf) 
{ 
DnsHead *DnsH; 
DnsQuery *DnsQ; 
int NameLen; 
memset(buf,0,sizeof(DnsHead)); 
//設置頭部 
DnsH = (DnsHead *)buf; 
DnsH->ID = (USHORT)1; 
DnsH->tag = htons(0x0100); 
DnsH->numQ = htons(1); 
DnsH->numA = 0; 
DnsQ =(DnsQuery *) ( buf+ sizeof(DnsHead) ); 
NameLen = ChName(name,(char *)DnsQ); 
//設置查詢信息 
DnsQ = (DnsQuery *)( (char *)DnsQ + NameLen ); 
DnsQ->classes = htons(1); 
DnsQ->type = htons(1); 
return true; 
} 
//顯示錯誤信息 
void displayErrWSA(char *str) 
{ 
printf("\n%s,err = %d\n",str,WSAGetLastError()); 
getchar(); 
} 
//域名轉化 
int ChName(char *fname,char *tname) 
{ 
int j =0; 
int i =strlen(fname)-1; 
int k = i+1; 
tname[i+2] = 0; 
for (; i>=0;i--,k--) 
{ 
if (fname[i] == '.') 
{ 
tname[k] = j; 
j=0; 
} 
else 
{ 
tname[k] = fname[i]; 
j++; 
} 
} 
tname[k] = j; 
return strlen(tname)+1; 
}